Re: [drakelist] AC-4R upgrades

[Ken Winterling]

"Ken Winterling" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
According to Tom this supply also had an open 10K HV bleeder/load
resistor.  Whatever caused it to fail may have caused the 220K
resistor to fail.  I'm waiting for Tom's response to see what he
found.

Ken, WA2LBI

On 1/15/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:


An open 220k bleeder resistor makes sense. I guess you could check that by
disconnecting it and checking the resistance. Makes me wonder what would
cause it to fail. Assuming 250 volts it would need to dissipate 0.28 watt.
If it's a 1/2 watt carbon composition resistor, it might have increased in
value over time. Those resistors are known to do that.
-- Original message --
From: "Ken Winterling" <[EMAIL PROTECTED]>

>
> "Ken Winterling" made an utterance to the drakelist
> gang
>
--
> Tom,
>
> There is a 220K bleeder/load resistor, R8, across the medium B+, 250V,
> supply to ground. If it is open the medium B+ will be pulled up
> toward the HV. Let us know what you find.
>
> Ken, WA2LBI
> >
> > On 1/14/07, Tom Taylor wrote:
> > > Still working on the AC-3... The drakelist wisdom was the 20k load
resistor
> > > didn't present enough of a load, compared to the original 10k
resistor, and
> > > that was the reason the HV kept climbing. I ordered a 10k 10w re
sistor and
> > > it recently arrived and I installed it in place. Note that this
resistor
> > > connects the HV+ with the medium voltage B+ (which seems odd). With
this new
> > > resistor, the HV now reads a reasonable and respectable 720v (no
load).
> > > That's good. But the medium voltage now reads 570v !!! I can't explain
it.
> > > What's different about the medium voltage supply is I replaced the two
100
> > > uf caps with 330 uf caps and the 80 uf cap with a 120 uf. That's what
I had
> > > in my junk box. Why is that supply so over-voltage now? Perhaps I have
a
> > > wiring error, though I carefully checked for errors.
> > >
> > > Thanks,
> > > Tom n7tm
> > >
> >
>
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Re: [drakelist] AC-4R upgrades

[Ken Winterling]

"Ken Winterling" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
Tom,

There is a 220K bleeder/load resistor, R8, across the medium B+, 250V,
supply to ground.  If it is open the medium B+ will be pulled up
toward the HV.  Let us know what you find.

Ken, WA2LBI


On 1/14/07, Tom Taylor <[EMAIL PROTECTED]> wrote:
> Still working on the AC-3... The drakelist wisdom was the 20k load resistor
> didn't present enough of a load, compared to the original 10k resistor, and
> that was the reason the HV kept climbing. I ordered a 10k 10w resistor and
> it recently arrived and I installed it in place. Note that this resistor
> connects the HV+ with the medium voltage B+ (which seems odd). With this new
> resistor, the HV now reads a reasonable and respectable 720v (no load).
> That's good. But the medium voltage now reads 570v !!! I can't explain it.
> What's different about the medium voltage supply is I replaced the two 100
> uf caps with 330 uf caps and the 80 uf cap with a 120 uf. That's what I had
> in my junk box. Why is that supply so over-voltage now? Perhaps I have a
> wiring error, though I carefully checked for errors.
>
> Thanks,
> Tom n7tm
>


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Re: [drakelist] AC-4R upgrades

[w1id]

An open 220k bleeder resistor makes sense. I guess you could check that by 
disconnecting it and checking the resistance. Makes me wonder what would cause 
it to fail. Assuming 250 volts it would need to dissipate 0.28 watt. If it's a 
1/2 watt carbon composition resistor, it might have increased in value over 
time. Those resistors are known to do that.
-- Original message -- 
From: "Ken Winterling" <[EMAIL PROTECTED]> 

> 
> "Ken Winterling" made an utterance to the drakelist 
> gang 
> -- 
> Tom, 
> 
> There is a 220K bleeder/load resistor, R8, across the medium B+, 250V, 
> supply to ground. If it is open the medium B+ will be pulled up 
> toward the HV. Let us know what you find. 
> 
> Ken, WA2LBI 
> > 
> > On 1/14/07, Tom Taylor wrote: 
> > > Still working on the AC-3... The drakelist wisdom was the 20k load 
> > > resistor 
> > > didn't present enough of a load, compared to the original 10k resistor, 
> > > and 
> > > that was the reason the HV kept climbing. I ordered a 10k 10w resistor 
> > > and 
> > > it recently arrived and I installed it in place. Note that this resistor 
> > > connects the HV+ with the medium voltage B+ (which seems odd). With this 
> > > new 
> > > resistor, the HV now reads a reasonable and respectable 720v (no load). 
> > > That's good. But the medium voltage now reads 570v !!! I can't explain 
> > > it. 
> > > What's different about the medium voltage supply is I replaced the two 
> > > 100 
> > > uf caps with 330 uf caps and the 80 uf cap with a 120 uf. That's what I 
> > > had 
> > > in my junk box. Why is that supply so over-voltage now? Perhaps I have a 
> > > wiring error, though I carefully checked for errors. 
> > > 
> > > Thanks, 
> > > Tom n7tm 
> > > 
> > 
> -- 
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Re: [drakelist] AC-4R upgrades

[Tom Taylor]

I lifted the 220k bleeder from ground and it measured about 230k, probably
not enough of a change to account for such a high voltage. I soldered the
bleeder back to ground and untied the connection between the 10k 25w load
resistor between the HV and 250v supply. The 250v supply now reads a
reasonable 270v while the HV rises out of control (+900v). Reconnecting that
10k back to the 250v supply, the 250v reads over 500v.

I don't "get" how that 10k load resistor is supposed to work? It would make
more sense to me if it was tied to ground, but the only way it's getting to
ground is through the puny 220k 1/2w resistor on the 250v supply.

Tom

On 1/15/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:


An open 220k bleeder resistor makes sense. I guess you could check that by
disconnecting it and checking the resistance. Makes me wonder what would
cause it to fail. Assuming 250 volts it would need to dissipate 0.28 watt.
If it's a 1/2 watt carbon composition resistor, it might have increased in
value over time. Those resistors are known to do that.

-- Original message --
From: "Ken Winterling" <[EMAIL PROTECTED]>

>
> "Ken Winterling" made an utterance to the drakelist
> gang
> --
> Tom,
>
> There is a 220K bleeder/load resistor, R8, across the medium B+, 250V,
> supply to ground. If it is open the medium B+ will be pulled up
> toward the HV. Let us know what you find.
>
> Ken, WA2LBI
> >
> > On 1/14/07, Tom Taylor wrote:
> > > Still working on the AC-3... The drakelist wisdom was the 20k load
resistor
> > > didn't present enough of a load, compared to the original 10k
resistor, and
> > > that was the reason the HV kept climbing. I ordered a 10k 10w re
sistor and
> > > it recently arrived and I installed it in place. Note that this
resistor
> > > connects the HV+ with the medium voltage B+ (which seems odd). With
this new
> > > resistor, the HV now reads a reasonable and respectable 720v (no
load).
> > > That's good. But the medium voltage now reads 570v !!! I can't
explain it.
> > > What's different about the medium voltage supply is I replaced the
two 100
> > > uf caps with 330 uf caps and the 80 uf cap with a 120 uf. That's
what I had
> > > in my junk box. Why is that supply so over-voltage now? Perhaps I
have a
> > > wiring error, though I carefully checked for errors.
> > >
> > > Thanks,
> > > Tom n7tm
> > >
> >
> --
> Submissions: drakelist@www.zerobeat.net
> Unsubscribe: m [EMAIL PROTECTED] - unsubscribe drakelist in body

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Re: [drakelist] AC-4R upgrades

[Tom Taylor]

 numbers of hours at some temperature. Component manufacturers usually
> try to
> embellish the specifications and say their caps will take 1000 hours of
> use
> at room temperature. But in actual operation ambient temperature will be
> higher than 25 degrees C and they typically don't say too much about
> self
> heating due to ripple current which brings up temperature even more.
> This is
> why it is always best to over rate voltage in electrolytics when
> selecting
> components. I see that Drake realized this was not a good design and
> soon
> changed to a capacitive input supply which is better suited to SSB
> service,
> and less expensive. As far as I'm concerned I would avoid the original
> AC-3
> in daily use. You wisely chose to use it on the test bench instead.
>
> -Original Message-
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] ] On Behalf Of Donnie Garrett
> Sent: Tuesday, December 12, 2006 5:27 AM
> To: Tom Taylor
> Cc: drakelist@www.zerobeat.net
> Subject: Re: [drakelist] AC-4R upgrades
>
>
> "Donnie Garrett" <[EMAIL PROTECTED]> made an utterance to the drakelist
> gang
> --
> Tom:
> I have one of the early AC3 supplies that used a HV choke.  Garey
> K4OAH and I had a lot of discussions about its design some time back
> after I discovered the ceramic 25W load resistor was open.  You better
> check yours to see if its OK.  It will still operate but the no load
> HV will float very high with an open load resistor.  I was never able
> to find an exact replacement at the time I needed it so I installed a
> 25W wire-wound resistor in a vertical fashion with a small bolt
> running through it. Somewhat similar to the original setup. I choose a
> 25K 25W instead of a 15K to reduce the heat dissipation produced by
> the resistor.  The 25K still loaded down the HV and was near the same
> as was prior with the original 15K 25W resistor which seems to
> regularly fail due to running it at or near it's maxium wattage
> dissipation.
> Also one last thing, If I recall the HV winding on this early choke
> version AC3 was higher than the later AC3 and AC4's that didn't use
> the HV choke.  Seems I temporally jumped across this choke just to see
> what effect it had on the HV and if I recall correctly the HV jumped
> up in voltage considerably, and was then out of speck and was near the
> max voltage ratings of the 2 HV caps. (No Good)  I would appreciate
> your findings on the HV secondary windings if you don't mind.
> Too put it quite frankly I don't care for the early model AC3 choke
> type supply due to these issues.  The only nice thing about this model
> is that all the caps mount on the underside of its chassis.  This AC3
> supply now serves as my test bench supply and is not used in my
> station.
>
> Hope this helps, Don / WA9TGT
>
>
>
> On 12/11/06, Tom Taylor <[EMAIL PROTECTED] > wrote:
> > I have a number of Drake A, B, and C twin combos. I decided to upgrade
> all
> the power supplies with AC-4R boards. Since most of the caps are now 30
> to
> 40 years old, I don't want to risk a bias supply going out and ruining
> the
> finals or some short ruining the transformers. I order a bunch of blank
> boards since I already had some of the parts. The rest of the parts I
> ordered from DigiKey. I assembled all the boards at the same time and
> then
> started upgrading the AC-4s, one by one.
> >
> > So far, all of the power supplies are different in one way or another
> and
> all of them have been modified by previous owners. Here are some
> examples:
> >
> > #1) A previous owner replace the mid-voltage supplies' capacitors with
> a
> bundle of three caps mounted to the upper end the supply.
> >
> > #2) A previous owner replaced the sand resistor below the chassis with
> two
> higher wattage resistors mounted to the upper end of the supply.
> >
> > #3) A previous owner replaced one of the diodes in the HV supply. The
> transformer in this supply has transformer bolts inserted the wrong
> direction to mount the AC-4R board. Unfortunately, it's not as simple as
> removing the bolts and inserting them in the other direction because the
> bolts are just long enough to reach, but not long enough to add the
> board
> spacers.
> >
> > #4) This is an AC-3, serial #101. I've never seen a Drake power supply
> like this. There's a large choke mounted adjacent to the transformer.
> All of
> the other parts, including the capacitors, are radial lead caps that are
>
> packed underneath the very low chassis. Has anyone else seen an early
> AC-3
> like this? I'm planning to remove the choke and rebuilding the supply
> just
> like all of the others since all of the circuitry is now on the AC-4R
> board.
> >
> > Thanks,
> > Tom N7TM
> >
>
>
>
> --
> WA9TGT / Don Garrett / Muncie, IN
> "Unique Radio Parts" www.wa9tgt.com
> --
> Submissions:drakelist@www.zerobeat.net
> Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist
> in
> body
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> --
>
>
>

Re: [drakelist] AC-4R upgrades

[Tom Taylor]

I replaced the diodes and capacitors in the early AC-3 w/choke power supply.
I used what I had on hand. The HV caps, originally 350v 80 uf, are now 450v
120 uf. The 10k HV load resistor was open. I replaced it with what I had, a
20k 50w resistor. While testing the refurbished supply last Thursday night,
the Northwest was hit with a terrific wind storm and our power was knocked
out at that instant. We're on our eigth day without power at home (have
power and internet here at work). I've posted pictures of the trees and
power lines here:
http://www.advrider.com/forums/showthread.php?t=189994&highlight=northwest+wind+storm

Unfortunately, the HV exhibits the behavior you mentioned in your reply.
While measuring the HV on power up, the voltage quickly climbs to 850v, then
continues to climb at a slower rate to over 900v. At 920v (past the voltage
limit of the two series caps), I pulled the plug. Is the fact that the
voltage is climbing so high not under load indicating that my load resistor
is not loading the HV enough? The old value was 10k, the new value is 20k.
With values that high, I figured it wouldn't matter much, but perhaps it
does.

I have a couple comments after converting several AC-3's and AC-4's to use
the AC-4R replacement board:
- the supplies really did change over the years. One example, my "newest"
AC-4 has a 120/220v switch and a 3 wire plug, but none of the others do
- I'm surprised by the very small gauge wires in the wire bundle supplying
the xmtr. That HV wire is so thinly insulated -- no more so than any of the
other wires.

Has anyone else converted an AC-3 (the non-choke model) to use the AC-4R
board? I mounted the board on standoffs on top of the chassis. I'd hate to
reach around the back of an MS-4 enclosure to adjust the bias pot (which is
on top of the AC-3 chassis) and touch the open AC-4R board. There's some
serious voltage -- and a lot of stored energy with the new caps -- right
there. Has anyone built a little cage around the board? Seems like a lot of
work, but perhaps worth it.

Tom n7tm
On 12/12/06, Gerry <[EMAIL PROTECTED]> wrote:


What you describe is typical of choke input power supplies. Text books
tell
us that choke input supplies are better at regulation but that is simply
not
true if you have a wide ranging dynamic load. Choke input power supplies
require a minimum load. There are formulas in the old handbooks to
calculate
the value of resistance to draw a proper load current. Without a minimum
load it would be as if no choke existed (except for its DC resistance) and
the filter capacitors will charge to 1.414 times the value of AC rms. In
other words, if you have 750VAC secondary the capacitors will charge to
over
1,060 volts with no load! With a properly chosen resistor this would be
0.9
times 750 volts or 675 volts. Please note the HV filter capacitors are
only
rated to 350 volts for a total of only 700 volts. So as you can see, the
10k, 20w load resistor on the output of the HV side of the supply is
crucial. That resistor dissipates around 16 watts. Notice that the low end
is referenced to +250V and not ground. It should be rated for twice the
actual power dissipation or 32 watts. Put it another way, without the load
resistor, key up voltage would be around 1kV while key down would drop to
about 675 volts. I should mention that the choke has DC resistance which
may
be a significant contributor to voltage drop. If you draw 450 mils and
your
DC choke has 50 Ohms of DC resistance, you will drop an additional 22.5
volts across the choke. Also look at the +250 volt side and see that the
filter caps are rated to only 300 volts. This is much too close for
comfort
and is really a very slim margin of safety. Typically the voltage rating
of
electrolytics is related to the maximum voltage it can withstand for a
given
numbers of hours at some temperature. Component manufacturers usually try
to
embellish the specifications and say their caps will take 1000 hours of
use
at room temperature. But in actual operation ambient temperature will be
higher than 25 degrees C and they typically don't say too much about self
heating due to ripple current which brings up temperature even more. This
is
why it is always best to over rate voltage in electrolytics when selecting
components. I see that Drake realized this was not a good design and soon
changed to a capacitive input supply which is better suited to SSB
service,
and less expensive. As far as I'm concerned I would avoid the original
AC-3
in daily use. You wisely chose to use it on the test bench instead.

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Donnie Garrett
Sent: Tuesday, December 12, 2006 5:27 AM
To: Tom Taylor
Cc: drakelist@www.zerobeat.net
Subject: Re: [drakelist] AC-4R upgrades


"Donnie Garrett" <[EMAIL PROTECTED]> made an utterance to the drakelist
gang
---

Re: [drakelist] AC-4R upgrades

[Garey Barrell]

Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
Denny -

Absolutely. 


However ...

The Drake supply in question varies over a roughly 3:1 ratio, i.e., 100 
mA "idling" to ~ 330 mA "full load", at an audio rate for SSB or a rate 
determined by CW keying speed, NOT including bleeder current, which is 
constant.


73, Garey - K4OAH
Atlanta

Drake 2-B, 4-B & C-Line Service Supplement CDs




Dennis Monticelli wrote:


"Dennis Monticelli" <[EMAIL PROTECTED]> made an utterance to 
the drakelist gang

--
My company makes chips for switching supplies.  One important design
choice is whether or not to allow the filter inductor to operate in
"discontinuous mode."  This simply means that the current through the
inductor is not continous; it runs out of stored energy each cycle as
the current drops to zero.  When that happens its filtering action is
impaired.

An old fashioned tube supply with a choke is no differrent even though
the frequency is much lower.  If the choke has insufficient inductance
for the minimum load current, then it will "run dry" before the next
cycle of the line voltage replenishes the energy.  Wwhen that happens
its ability to regulate the output voltage is seriously impaired and
the output soars to 1.4 times the RMS.  This is why Gerry recommends
that the minimum load represented by the stock bleed resistor be
heeded.  To paraphrase Gerry, only use choke input supplies when the
load current range is relatively narrow; 10:1 is too much.

Denny AE6C

On 12/12/06, Gerry <[EMAIL PROTECTED]> wrote:


"Gerry" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
What you describe is typical of choke input power supplies. Text 
books tell
us that choke input supplies are better at regulation but that is 
simply not

true if you have a wide ranging dynamic load. Choke input power supplies
require a minimum load. There are formulas in the old handbooks to 
calculate

the value of resistance to draw a proper load current. Without a minimum
load it would be as if no choke existed (except for its DC 
resistance) and

the filter capacitors will charge to 1.414 times the value of AC rms. In
other words, if you have 750VAC secondary the capacitors will charge 
to over
1,060 volts with no load! With a properly chosen resistor this would 
be 0.9
times 750 volts or 675 volts. Please note the HV filter capacitors 
are only

rated to 350 volts for a total of only 700 volts. So as you can see, the
10k, 20w load resistor on the output of the HV side of the supply is
crucial. That resistor dissipates around 16 watts. Notice that the 
low end

is referenced to +250V and not ground. It should be rated for twice the
actual power dissipation or 32 watts. Put it another way, without the 
load
resistor, key up voltage would be around 1kV while key down would 
drop to
about 675 volts. I should mention that the choke has DC resistance 
which may
be a significant contributor to voltage drop. If you draw 450 mils 
and your

DC choke has 50 Ohms of DC resistance, you will drop an additional 22.5
volts across the choke. Also look at the +250 volt side and see that the
filter caps are rated to only 300 volts. This is much too close for 
comfort
and is really a very slim margin of safety. Typically the voltage 
rating of
electrolytics is related to the maximum voltage it can withstand for 
a given
numbers of hours at some temperature. Component manufacturers usually 
try to
embellish the specifications and say their caps will take 1000 hours 
of use

at room temperature. But in actual operation ambient temperature will be
higher than 25 degrees C and they typically don't say too much about 
self
heating due to ripple current which brings up temperature even more. 
This is
why it is always best to over rate voltage in electrolytics when 
selecting
components. I see that Drake realized this was not a good design and 
soon
changed to a capacitive input supply which is better suited to SSB 
service,
and less expensive. As far as I'm concerned I would avoid the 
original AC-3

in daily use. You wisely chose to use it on the test bench instead.

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Donnie Garrett
Sent: Tuesday, December 12, 2006 5:27 AM
To: Tom Taylor
Cc: drakelist@www.zerobeat.net
Subject: Re: [drakelist] AC-4R upgrades


"Donnie Garrett" <[EMAIL PROTECTED]> made an utterance to the 
drakelist gang

--
Tom:
I have one of the early AC3 supplies that used a HV choke.  Garey
K4OAH and I had a lot of discussions about its design some time back
after I discovered t

Re: [drakelist] AC-4R upgrades

[Donnie Garrett]

"Donnie Garrett" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
Tom:
I have one of the early AC3 supplies that used a HV choke.  Garey
K4OAH and I had a lot of discussions about its design some time back
after I discovered the ceramic 25W load resistor was open.  You better
check yours to see if its OK.  It will still operate but the no load
HV will float very high with an open load resistor.  I was never able
to find an exact replacement at the time I needed it so I installed a
25W wire-wound resistor in a vertical fashion with a small bolt
running through it. Somewhat similar to the original setup. I choose a
25K 25W instead of a 15K to reduce the heat dissipation produced by
the resistor.  The 25K still loaded down the HV and was near the same
as was prior with the original 15K 25W resistor which seems to
regularly fail due to running it at or near it's maxium wattage
dissipation.
Also one last thing, If I recall the HV winding on this early choke
version AC3 was higher than the later AC3 and AC4's that didn't use
the HV choke.  Seems I temporally jumped across this choke just to see
what effect it had on the HV and if I recall correctly the HV jumped
up in voltage considerably, and was then out of speck and was near the
max voltage ratings of the 2 HV caps. (No Good)  I would appreciate
your findings on the HV secondary windings if you don't mind.
Too put it quite frankly I don't care for the early model AC3 choke
type supply due to these issues.  The only nice thing about this model
is that all the caps mount on the underside of its chassis.  This AC3
supply now serves as my test bench supply and is not used in my
station.

Hope this helps, Don / WA9TGT



On 12/11/06, Tom Taylor <[EMAIL PROTECTED]> wrote:

I have a number of Drake A, B, and C twin combos. I decided to upgrade all the 
power supplies with AC-4R boards. Since most of the caps are now 30 to 40 years 
old, I don't want to risk a bias supply going out and ruining the finals or 
some short ruining the transformers. I order a bunch of blank boards since I 
already had some of the parts. The rest of the parts I ordered from DigiKey. I 
assembled all the boards at the same time and then started upgrading the AC-4s, 
one by one.

So far, all of the power supplies are different in one way or another and all 
of them have been modified by previous owners. Here are some examples:

#1) A previous owner replace the mid-voltage supplies' capacitors with a bundle 
of three caps mounted to the upper end the supply.

#2) A previous owner replaced the sand resistor below the chassis with two 
higher wattage resistors mounted to the upper end of the supply.

#3) A previous owner replaced one of the diodes in the HV supply. The 
transformer in this supply has transformer bolts inserted the wrong direction 
to mount the AC-4R board. Unfortunately, it's not as simple as removing the 
bolts and inserting them in the other direction because the bolts are just long 
enough to reach, but not long enough to add the board spacers.

#4) This is an AC-3, serial #101. I've never seen a Drake power supply like 
this. There's a large choke mounted adjacent to the transformer. All of the 
other parts, including the capacitors, are radial lead caps that are packed 
underneath the very low chassis. Has anyone else seen an early AC-3 like this? 
I'm planning to remove the choke and rebuilding the supply just like all of the 
others since all of the circuitry is now on the AC-4R board.

Thanks,
Tom N7TM





--
WA9TGT / Don Garrett / Muncie, IN
"Unique Radio Parts" www.wa9tgt.com
--
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RE: [drakelist] AC-4R upgrades

[Gerry]

"Gerry" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
What you describe is typical of choke input power supplies. Text books tell
us that choke input supplies are better at regulation but that is simply not
true if you have a wide ranging dynamic load. Choke input power supplies
require a minimum load. There are formulas in the old handbooks to calculate
the value of resistance to draw a proper load current. Without a minimum
load it would be as if no choke existed (except for its DC resistance) and
the filter capacitors will charge to 1.414 times the value of AC rms. In
other words, if you have 750VAC secondary the capacitors will charge to over
1,060 volts with no load! With a properly chosen resistor this would be 0.9
times 750 volts or 675 volts. Please note the HV filter capacitors are only
rated to 350 volts for a total of only 700 volts. So as you can see, the
10k, 20w load resistor on the output of the HV side of the supply is
crucial. That resistor dissipates around 16 watts. Notice that the low end
is referenced to +250V and not ground. It should be rated for twice the
actual power dissipation or 32 watts. Put it another way, without the load
resistor, key up voltage would be around 1kV while key down would drop to
about 675 volts. I should mention that the choke has DC resistance which may
be a significant contributor to voltage drop. If you draw 450 mils and your
DC choke has 50 Ohms of DC resistance, you will drop an additional 22.5
volts across the choke. Also look at the +250 volt side and see that the
filter caps are rated to only 300 volts. This is much too close for comfort
and is really a very slim margin of safety. Typically the voltage rating of
electrolytics is related to the maximum voltage it can withstand for a given
numbers of hours at some temperature. Component manufacturers usually try to
embellish the specifications and say their caps will take 1000 hours of use
at room temperature. But in actual operation ambient temperature will be
higher than 25 degrees C and they typically don't say too much about self
heating due to ripple current which brings up temperature even more. This is
why it is always best to over rate voltage in electrolytics when selecting
components. I see that Drake realized this was not a good design and soon
changed to a capacitive input supply which is better suited to SSB service,
and less expensive. As far as I'm concerned I would avoid the original AC-3
in daily use. You wisely chose to use it on the test bench instead.

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Donnie Garrett
Sent: Tuesday, December 12, 2006 5:27 AM
To: Tom Taylor
Cc: drakelist@www.zerobeat.net
Subject: Re: [drakelist] AC-4R upgrades


"Donnie Garrett" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
Tom:
I have one of the early AC3 supplies that used a HV choke.  Garey
K4OAH and I had a lot of discussions about its design some time back
after I discovered the ceramic 25W load resistor was open.  You better
check yours to see if its OK.  It will still operate but the no load
HV will float very high with an open load resistor.  I was never able
to find an exact replacement at the time I needed it so I installed a
25W wire-wound resistor in a vertical fashion with a small bolt
running through it. Somewhat similar to the original setup. I choose a
25K 25W instead of a 15K to reduce the heat dissipation produced by
the resistor.  The 25K still loaded down the HV and was near the same
as was prior with the original 15K 25W resistor which seems to
regularly fail due to running it at or near it's maxium wattage
dissipation.
Also one last thing, If I recall the HV winding on this early choke
version AC3 was higher than the later AC3 and AC4's that didn't use
the HV choke.  Seems I temporally jumped across this choke just to see
what effect it had on the HV and if I recall correctly the HV jumped
up in voltage considerably, and was then out of speck and was near the
max voltage ratings of the 2 HV caps. (No Good)  I would appreciate
your findings on the HV secondary windings if you don't mind.
Too put it quite frankly I don't care for the early model AC3 choke
type supply due to these issues.  The only nice thing about this model
is that all the caps mount on the underside of its chassis.  This AC3
supply now serves as my test bench supply and is not used in my
station.

Hope this helps, Don / WA9TGT



On 12/11/06, Tom Taylor <[EMAIL PROTECTED]> wrote:
> I have a number of Drake A, B, and C twin combos. I decided to upgrade all
the power supplies with AC-4R boards. Since most of the caps are now 30 to
40 years old, I don't want to risk a bias supply going out and ruining the
finals or some short ruin

Re: [drakelist] AC-4R upgrades

[Garey Barrell]

Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
Gerry -

One other factor.  Electrolytic capacitors of that era were rated in DC 
Working Volts (DCWV), with a peak voltage of some 30-40% higher.  So in 
the terminology of the day, a 300 DCWV capacitor would be a reasonable 
choice for the filter of a 250V supply.


Take a look at the bottom chassis photo of an early AC-3 at

<http://www.wb4hfn.com/DRAKE/DrakeEquipmentPictures/Equip_EarlyAC3_Bottom.htm>

and you'll note that the HV filter capacitors are clearly marked 450 WVDC.

I think the only problem with the AC-3 was that the  _necessary_  
"minimum load" resistor was undersized, even considering that it was 
returned to the +250V supply rather than ground.  Kinda makes you wonder 
if Drake got a good buy on those resistors!  Or perhaps that was the 
largest one available in that "single-ended" style.  The choke supply IS 
more tightly regulated than a capacitor only version,  _IF_  the minimum 
load is maintained by an intact bleeder resistor. 


73, Garey - K4OAH
Atlanta

Drake 2-B, 4-B & C-Line Service Supplement CDs




Gerry wrote:

"Gerry" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
What you describe is typical of choke input power supplies. Text books tell
us that choke input supplies are better at regulation but that is simply not
true if you have a wide ranging dynamic load. Choke input power supplies
require a minimum load. There are formulas in the old handbooks to calculate
the value of resistance to draw a proper load current. Without a minimum
load it would be as if no choke existed (except for its DC resistance) and
the filter capacitors will charge to 1.414 times the value of AC rms. In
other words, if you have 750VAC secondary the capacitors will charge to over
1,060 volts with no load! With a properly chosen resistor this would be 0.9
times 750 volts or 675 volts. Please note the HV filter capacitors are only
rated to 350 volts for a total of only 700 volts. So as you can see, the
10k, 20w load resistor on the output of the HV side of the supply is
crucial. That resistor dissipates around 16 watts. Notice that the low end
is referenced to +250V and not ground. It should be rated for twice the
actual power dissipation or 32 watts. Put it another way, without the load
resistor, key up voltage would be around 1kV while key down would drop to
about 675 volts. I should mention that the choke has DC resistance which may
be a significant contributor to voltage drop. If you draw 450 mils and your
DC choke has 50 Ohms of DC resistance, you will drop an additional 22.5
volts across the choke. Also look at the +250 volt side and see that the
filter caps are rated to only 300 volts. This is much too close for comfort
and is really a very slim margin of safety. Typically the voltage rating of
electrolytics is related to the maximum voltage it can withstand for a given
numbers of hours at some temperature. Component manufacturers usually try to
embellish the specifications and say their caps will take 1000 hours of use
at room temperature. But in actual operation ambient temperature will be
higher than 25 degrees C and they typically don't say too much about self
heating due to ripple current which brings up temperature even more. This is
why it is always best to over rate voltage in electrolytics when selecting
components. I see that Drake realized this was not a good design and soon
changed to a capacitive input supply which is better suited to SSB service,
and less expensive. As far as I'm concerned I would avoid the original AC-3
in daily use. You wisely chose to use it on the test bench instead.

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Donnie Garrett
Sent: Tuesday, December 12, 2006 5:27 AM
To: Tom Taylor
Cc: drakelist@www.zerobeat.net
Subject: Re: [drakelist] AC-4R upgrades


"Donnie Garrett" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
Tom:
I have one of the early AC3 supplies that used a HV choke.  Garey
K4OAH and I had a lot of discussions about its design some time back
after I discovered the ceramic 25W load resistor was open.  You better
check yours to see if its OK.  It will still operate but the no load
HV will float very high with an open load resistor.  I was never able
to find an exact replacement at the time I needed it so I installed a
25W wire-wound resistor in a vertical fashion with a small bolt
running through it. Somewhat similar to the original setup. I choose a
25K 25W instead of a 15K to reduce the heat dissipation produced by
the resistor.  The 25K still loaded down the HV and was near the same
as was prior with the origin

Re: [drakelist] AC-4R upgrades

[Tom Taylor]

Hey, thanks for the tip! I just checked the vertical ceramic load resistor
and it is open, just like yours. Last night I decided to just replace all
the electrolytic capacitors under the chassis (and the diodes as well).
Before clipping out the old parts, I took voltage measurements so I'd have a
baseline to test against after replacing the capacitors. The HV seemed
unusually high at 854 vdc. The open load resistor probably explains that
very HV.

Thanks,
Tom

On 12/12/06, Donnie Garrett <[EMAIL PROTECTED]> wrote:


Tom:
I have one of the early AC3 supplies that used a HV choke.  Garey
K4OAH and I had a lot of discussions about its design some time back
after I discovered the ceramic 25W load resistor was open.  You better
check yours to see if its OK.  It will still operate but the no load
HV will float very high with an open load resistor.  I was never able
to find an exact replacement at the time I needed it so I installed a
25W wire-wound resistor in a vertical fashion with a small bolt
running through it. Somewhat similar to the original setup. I choose a
25K 25W instead of a 15K to reduce the heat dissipation produced by
the resistor.  The 25K still loaded down the HV and was near the same
as was prior with the original 15K 25W resistor which seems to
regularly fail due to running it at or near it's maxium wattage
dissipation.
Also one last thing, If I recall the HV winding on this early choke
version AC3 was higher than the later AC3 and AC4's that didn't use
the HV choke.  Seems I temporally jumped across this choke just to see
what effect it had on the HV and if I recall correctly the HV jumped
up in voltage considerably, and was then out of speck and was near the
max voltage ratings of the 2 HV caps. (No Good)  I would appreciate
your findings on the HV secondary windings if you don't mind.
Too put it quite frankly I don't care for the early model AC3 choke
type supply due to these issues.  The only nice thing about this model
is that all the caps mount on the underside of its chassis.  This AC3
supply now serves as my test bench supply and is not used in my
station.

Hope this helps, Don / WA9TGT



On 12/11/06, Tom Taylor <[EMAIL PROTECTED]> wrote:
> I have a number of Drake A, B, and C twin combos. I decided to upgrade
all the power supplies with AC-4R boards. Since most of the caps are now 30
to 40 years old, I don't want to risk a bias supply going out and ruining
the finals or some short ruining the transformers. I order a bunch of blank
boards since I already had some of the parts. The rest of the parts I
ordered from DigiKey. I assembled all the boards at the same time and then
started upgrading the AC-4s, one by one.
>
> So far, all of the power supplies are different in one way or another
and all of them have been modified by previous owners. Here are some
examples:
>
> #1) A previous owner replace the mid-voltage supplies' capacitors with a
bundle of three caps mounted to the upper end the supply.
>
> #2) A previous owner replaced the sand resistor below the chassis with
two higher wattage resistors mounted to the upper end of the supply.
>
> #3) A previous owner replaced one of the diodes in the HV supply. The
transformer in this supply has transformer bolts inserted the wrong
direction to mount the AC-4R board. Unfortunately, it's not as simple as
removing the bolts and inserting them in the other direction because the
bolts are just long enough to reach, but not long enough to add the board
spacers.
>
> #4) This is an AC-3, serial #101. I've never seen a Drake power supply
like this. There's a large choke mounted adjacent to the transformer. All of
the other parts, including the capacitors, are radial lead caps that are
packed underneath the very low chassis. Has anyone else seen an early AC-3
like this? I'm planning to remove the choke and rebuilding the supply just
like all of the others since all of the circuitry is now on the AC-4R board.
>
> Thanks,
> Tom N7TM
>



--
WA9TGT / Don Garrett / Muncie, IN
"Unique Radio Parts" www.wa9tgt.com

Re: [drakelist] AC-4R upgrades

[Dennis Monticelli]

"Dennis Monticelli" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
My company makes chips for switching supplies.  One important design
choice is whether or not to allow the filter inductor to operate in
"discontinuous mode."  This simply means that the current through the
inductor is not continous; it runs out of stored energy each cycle as
the current drops to zero.  When that happens its filtering action is
impaired.

An old fashioned tube supply with a choke is no differrent even though
the frequency is much lower.  If the choke has insufficient inductance
for the minimum load current, then it will "run dry" before the next
cycle of the line voltage replenishes the energy.  Wwhen that happens
its ability to regulate the output voltage is seriously impaired and
the output soars to 1.4 times the RMS.  This is why Gerry recommends
that the minimum load represented by the stock bleed resistor be
heeded.  To paraphrase Gerry, only use choke input supplies when the
load current range is relatively narrow; 10:1 is too much.

Denny AE6C

On 12/12/06, Gerry <[EMAIL PROTECTED]> wrote:


"Gerry" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
What you describe is typical of choke input power supplies. Text books tell
us that choke input supplies are better at regulation but that is simply not
true if you have a wide ranging dynamic load. Choke input power supplies
require a minimum load. There are formulas in the old handbooks to calculate
the value of resistance to draw a proper load current. Without a minimum
load it would be as if no choke existed (except for its DC resistance) and
the filter capacitors will charge to 1.414 times the value of AC rms. In
other words, if you have 750VAC secondary the capacitors will charge to over
1,060 volts with no load! With a properly chosen resistor this would be 0.9
times 750 volts or 675 volts. Please note the HV filter capacitors are only
rated to 350 volts for a total of only 700 volts. So as you can see, the
10k, 20w load resistor on the output of the HV side of the supply is
crucial. That resistor dissipates around 16 watts. Notice that the low end
is referenced to +250V and not ground. It should be rated for twice the
actual power dissipation or 32 watts. Put it another way, without the load
resistor, key up voltage would be around 1kV while key down would drop to
about 675 volts. I should mention that the choke has DC resistance which may
be a significant contributor to voltage drop. If you draw 450 mils and your
DC choke has 50 Ohms of DC resistance, you will drop an additional 22.5
volts across the choke. Also look at the +250 volt side and see that the
filter caps are rated to only 300 volts. This is much too close for comfort
and is really a very slim margin of safety. Typically the voltage rating of
electrolytics is related to the maximum voltage it can withstand for a given
numbers of hours at some temperature. Component manufacturers usually try to
embellish the specifications and say their caps will take 1000 hours of use
at room temperature. But in actual operation ambient temperature will be
higher than 25 degrees C and they typically don't say too much about self
heating due to ripple current which brings up temperature even more. This is
why it is always best to over rate voltage in electrolytics when selecting
components. I see that Drake realized this was not a good design and soon
changed to a capacitive input supply which is better suited to SSB service,
and less expensive. As far as I'm concerned I would avoid the original AC-3
in daily use. You wisely chose to use it on the test bench instead.

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Donnie Garrett
Sent: Tuesday, December 12, 2006 5:27 AM
To: Tom Taylor
Cc: drakelist@www.zerobeat.net
Subject: Re: [drakelist] AC-4R upgrades


"Donnie Garrett" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
Tom:
I have one of the early AC3 supplies that used a HV choke.  Garey
K4OAH and I had a lot of discussions about its design some time back
after I discovered the ceramic 25W load resistor was open.  You better
check yours to see if its OK.  It will still operate but the no load
HV will float very high with an open load resistor.  I was never able
to find an exact replacement at the time I needed it so I installed a
25W wire-wound resistor in a vertical fashion with a small bolt
running through it. Somewhat similar to the original setup. I choose a
25K 25W instead of a 15K to reduce the heat dissipation produced by
the resistor.  The 25K still loaded down the HV and was near the same
as was prior with the original 15K 25W res

Re: [drakelist] AC-4R upgrades

[Garey Barrell]

Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
Tom -

I don't think so.  I'm one of the worst for keeping things "original", 
but I don't think these units are THAT rare.  I guess you could keep the 
removed choke and try to avoid extra holes, but in all honesty I don't 
think it's worth losing any sleep over.   I guess you could stick it on 
"E*ay" and see if someone like Sindre wants to "preserve" it. 

The TR-3 was introduced in early 1963, probably at Dayton in April.  By 
October, it looks like they were up to about 3000 units, most of which 
were probably sold with an AC-3.  By September they were up to 2500 
AC-3s, and that MAY be when they dropped the choke.  By June 1964 they 
had built 10,000 TR-3s and were still using the "chokeless" AC-3 power 
supply.


The AC-4 came out in 1965, about the same time as the T-4X.  My VERY 
early T-4X was shipped with an AC-3 in September 1965.


73, Garey - K4OAH
Atlanta

Drake 2-B, 4-B & C-Line Service Supplement CDs




Tom Taylor wrote:
Would I be destroying something of historical worth by converting that 
early, and perhaps rare AC-3, to a modern supply? That would mean 
removing the choke and essentially all the parts underneath the 
chassis? The AC-4R (as I'm sure you're aware) replaces everything but 
the transformer, the cables, the connectors, and the bias pot.


On 12/11/06, *Garey Barrell* <[EMAIL PROTECTED] 
> wrote:


Tom -

Yeah, that's typical.  You're taking the right approach, since a
failure
in the Bias supply can take out more than just the finals, even if the
unit is in Standby.

#4.  Yes, this is a VERY early AC-3.  I don't know how many were
made,
but I've only seen a couple in 40 years of using/working on Drake
gear.
They work just fine, but your plan is reasonable.  Drake dropped the
choke, probably for  cost / weight / not needed  reasons.  The
primary
reason for it originally was to improve the regulation of the HV.

73, Garey - K4OAH
Atlanta

Drake 2-B, 4-B & C-Line Service Supplement CDs
http://www.k4oah.com>>



Tom Taylor wrote:
> I have a number of Drake A, B, and C twin combos. I decided to
upgrade
> all the power supplies with AC-4R boards. Since most of the caps are
> now 30 to 40 years old, I don't want to risk a bias supply going
out
> and ruining the finals or some short ruining the transformers. I
order
> a bunch of blank boards since I already had some of the parts. The
> rest of the parts I ordered from DigiKey. I assembled all the
boards
> at the same time and then started upgrading the AC-4s, one by one.
>
> So far, all of the power supplies are different in one way or
another
> and all of them have been modified by previous owners. Here are
some
> examples:
>
> #1) A previous owner replace the mid-voltage supplies'
capacitors with
> a bundle of three caps mounted to the upper end the supply.
>
> #2) A previous owner replaced the sand resistor below the
chassis with
> two higher wattage resistors mounted to the upper end of the supply.
>
> #3) A previous owner replaced one of the diodes in the HV
supply. The
> transformer in this supply has transformer bolts inserted the wrong
> direction to mount the AC-4R board. Unfortunately, it's not as
simple
> as removing the bolts and inserting them in the other direction
> because the bolts are just long enough to reach, but not long
enough
> to add the board spacers.
>
> #4) This is an AC-3, serial #101. I've never seen a Drake power
supply
> like this. There's a large choke mounted adjacent to the
transformer.
> All of the other parts, including the capacitors, are radial
lead caps
> that are packed underneath the very low chassis. Has anyone else
seen
> an early AC-3 like this? I'm planning to remove the choke and
> rebuilding the supply just like all of the others since all of the
> circuitry is now on the AC-4R board.
>
> Thanks,
> Tom N7TM



--
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Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body
Hopelessly Lost:[EMAIL PROTECTED] - help in body of message
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Re: [drakelist] AC-4R upgrades

[Garey Barrell]

Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
Tom -

Yeah, that's typical.  You're taking the right approach, since a failure 
in the Bias supply can take out more than just the finals, even if the 
unit is in Standby.


#4.  Yes, this is a VERY early AC-3.  I don't know how many were made, 
but I've only seen a couple in 40 years of using/working on Drake gear.  
They work just fine, but your plan is reasonable.  Drake dropped the 
choke, probably for  cost / weight / not needed  reasons.  The primary 
reason for it originally was to improve the regulation of the HV.


73, Garey - K4OAH
Atlanta

Drake 2-B, 4-B & C-Line Service Supplement CDs




Tom Taylor wrote:
I have a number of Drake A, B, and C twin combos. I decided to upgrade 
all the power supplies with AC-4R boards. Since most of the caps are 
now 30 to 40 years old, I don't want to risk a bias supply going out 
and ruining the finals or some short ruining the transformers. I order 
a bunch of blank boards since I already had some of the parts. The 
rest of the parts I ordered from DigiKey. I assembled all the boards 
at the same time and then started upgrading the AC-4s, one by one.


So far, all of the power supplies are different in one way or another 
and all of them have been modified by previous owners. Here are some 
examples:


#1) A previous owner replace the mid-voltage supplies' capacitors with 
a bundle of three caps mounted to the upper end the supply.


#2) A previous owner replaced the sand resistor below the chassis with 
two higher wattage resistors mounted to the upper end of the supply.


#3) A previous owner replaced one of the diodes in the HV supply. The 
transformer in this supply has transformer bolts inserted the wrong 
direction to mount the AC-4R board. Unfortunately, it's not as simple 
as removing the bolts and inserting them in the other direction 
because the bolts are just long enough to reach, but not long enough 
to add the board spacers.


#4) This is an AC-3, serial #101. I've never seen a Drake power supply 
like this. There's a large choke mounted adjacent to the transformer. 
All of the other parts, including the capacitors, are radial lead caps 
that are packed underneath the very low chassis. Has anyone else seen 
an early AC-3 like this? I'm planning to remove the choke and 
rebuilding the supply just like all of the others since all of the 
circuitry is now on the AC-4R board.


Thanks,
Tom N7TM

--
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Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body
Hopelessly Lost:[EMAIL PROTECTED] - help in body of message
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Re: [drakelist] AC-4R upgrades

[Tom Taylor]

Would I be destroying something of historical worth by converting that
early, and perhaps rare AC-3, to a modern supply? That would mean removing
the choke and essentially all the parts underneath the chassis? The AC-4R
(as I'm sure you're aware) replaces everything but the transformer, the
cables, the connectors, and the bias pot.

On 12/11/06, Garey Barrell <[EMAIL PROTECTED]> wrote:


Tom -

Yeah, that's typical.  You're taking the right approach, since a failure
in the Bias supply can take out more than just the finals, even if the
unit is in Standby.

#4.  Yes, this is a VERY early AC-3.  I don't know how many were made,
but I've only seen a couple in 40 years of using/working on Drake gear.
They work just fine, but your plan is reasonable.  Drake dropped the
choke, probably for  cost / weight / not needed  reasons.  The primary
reason for it originally was to improve the regulation of the HV.

73, Garey - K4OAH
Atlanta

Drake 2-B, 4-B & C-Line Service Supplement CDs




Tom Taylor wrote:
> I have a number of Drake A, B, and C twin combos. I decided to upgrade
> all the power supplies with AC-4R boards. Since most of the caps are
> now 30 to 40 years old, I don't want to risk a bias supply going out
> and ruining the finals or some short ruining the transformers. I order
> a bunch of blank boards since I already had some of the parts. The
> rest of the parts I ordered from DigiKey. I assembled all the boards
> at the same time and then started upgrading the AC-4s, one by one.
>
> So far, all of the power supplies are different in one way or another
> and all of them have been modified by previous owners. Here are some
> examples:
>
> #1) A previous owner replace the mid-voltage supplies' capacitors with
> a bundle of three caps mounted to the upper end the supply.
>
> #2) A previous owner replaced the sand resistor below the chassis with
> two higher wattage resistors mounted to the upper end of the supply.
>
> #3) A previous owner replaced one of the diodes in the HV supply. The
> transformer in this supply has transformer bolts inserted the wrong
> direction to mount the AC-4R board. Unfortunately, it's not as simple
> as removing the bolts and inserting them in the other direction
> because the bolts are just long enough to reach, but not long enough
> to add the board spacers.
>
> #4) This is an AC-3, serial #101. I've never seen a Drake power supply
> like this. There's a large choke mounted adjacent to the transformer.
> All of the other parts, including the capacitors, are radial lead caps
> that are packed underneath the very low chassis. Has anyone else seen
> an early AC-3 like this? I'm planning to remove the choke and
> rebuilding the supply just like all of the others since all of the
> circuitry is now on the AC-4R board.
>
> Thanks,
> Tom N7TM