Re: [Drakelist] Testing Caps for Leakage

[Dennis Monticelli]

Richard,

That is very true.  Paper caps can leak yet look OK for capacitance and not
too bad for ESR.  I think 5uA is too high for a paper cap.  If that cap is
being used for plate to grid coupling and the grid circuit is 1 Mohm, there
will obviously be a problem.

I have a common Heathkit IT-11 cap tester and I've calibrated the eye
closures for 1uA/10uA/1mA respectively on the leakage switch.  It tests caps
just fine and will form electrolytics.

Dennis AE6C

On Sat, Apr 2, 2011 at 10:07 PM, Richard Knoppow 1oldle...@ix.netcom.comwrote:

For years I thought it was sufficient to test caps for dissipation
 factor, another name for ESR, I discovered the hard way its not. Many will
 tell you that electrolytic caps must be tested with polarizing voltage and
 that may make a difference in the measured capacitance of some but that is
 not the problem I am discussing. I discovered that many caps develop low
 _parallel_ resistance AKA leakage. Not just electrolytic but also paper and
 probably other types of caps. I found this when I was getting an old General
 Radio signal generator going and discovered that the modulation monitor
 didn't work right. The coupling cap was a 0.05 uf high quality molded paper
 cap. It measured fine on a GR impedance bridge but a new cap fixed the
 problem. The new cap measured about the same as the old one on the bridge.
 So, I decided to measure the leakage current. I did this with a small GR
 regulated and adjustable power supply and a DMM capable of measuring
 micro-amps. Most DMM's and VOM's are sufficiently sensitive to work. I found
 the bad capacitor to have a lot of leakage current (can't remember how much)
 where a new one had none detectable. I used about 300V on that one because
 it was rated that high.
I then checked a bunch of discarded caps of all sorts plus some new
 ones. Bad electrolytics of course have very high leakage (right up to being
 sort circuits).
I think the limits are around 5 ua for paper or other non-electrolytic
 types and perhaps 15 ua or a bit more for electrolytics. The current for an
 electrolytic will drop as the virtual electrode forms, if it increases the
 thing is no good.
I later obtained a General Radio megohmeter,which will make a similar
 measurement but it has a fixed bias of 500V which is too much for many caps.
 It cqan be rigged to work with a lower voltage external supply, I have not
 tried that. The only advantage it has over the supply and meter method is
 that it indicates resistance directly.
Anyway, the point is (and you know what's coming) that many bad caps
 will test good on a bridge or capacitance meter that is not set up to
 measure _parallel_ resistance with sufficient voltage.
Note that _leakage_ or parallel resistance is also why bridging a bad
 cap with a good one will often NOT make a difference, its _not_ loss of
 capacitance but increase in leakage that's the problem and putting two caps
 in parallel won't change that. To investigate a cap it really is necessary
 to lift one end and substitute another.


 --
 Richard Knoppow
 Los Angeles
 WB6KBL
 dickb...@ix.netcom.com



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Re: [Drakelist] Testing Caps for Leakage

[Richard Knoppow]

-Original Message-
From: Dennis Monticelli 
Sent: Apr 3, 2011 1:22 AM
To: Richard Knoppow 1oldle...@ix.netcom.com
Cc: Drake List 
Subject: Re: [Drakelist] Testing Caps for Leakage

Richard,

That is very true. Paper caps can leak yet look OK for capacitance and not too bad for ESR. I think 5uA is too high for a paper cap. If that cap is being used for plate to grid coupling and the grid circuit is 1 Mohm, there will obviously be a problem.


I have a common Heathkit IT-11 cap tester and I've calibrated the eye closures for 1uA/10uA/1mA respectively on the leakage switch. It tests caps just fine and will form electrolytics.

Dennis AE6C
 I don't remember where I got the 5 uA value, you could well be right. It doesn't take much leakage to cause problems with coupling caps. Modern film caps have leakage so low its difficult to detect. 

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Re: [Drakelist] Fwd: My R-4B audio?

[Garey Barrell]

Lee -

Mike has the answer.  A leaky 0.1 uF coupling cap is the only, (also 
least likely!,) thing left.  I wondered about that last night, but the 
resistor was more likely, even a cracked solder joint!  :-)  Being right 
up against R137 doesn't help either.


Easy to check, just disconnect one end and see if the Q7 voltages go 
where they should be.


I would replace it with one of the Panasonic metalized polyester film 
caps rather than a ceramic.  It will actually be smaller than the 
ceramic, and a much better audio cap.


73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
www.k4oah.com


Mike Millen wrote:

Garey Barrell wrote:

Lee -

OK.  You need to measure resistor R131.  Q7 is NOT turned on at all,
there is no current through it.

The middle lead is the Collector, not the Base.  So the Base is 0.46
which isn't enough.   The Collector is 18V, indicating that there is
NO current through R148.  I suspect either R131 has way up in value,
or there is a cracked or rosin solder joint in that area.


I had the same problem  assumed Q7 had failed.

After changing Q7 with no improvement I determined that the only part 
left that would explain the fault

was a leaky C167, a 100nF ceramic.

It looked fine, but fitting a new one brought everything back to 
normal. (It was leaking away the bias from R131)


It's pretty unusual, but ceramics can go leaky, too.

73,
Mike



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Re: [Drakelist] Deoxit at Musician's Friend

[Karl du Roi]

Dear all,

have you had a look on amazon.com where I found a 5 oz tin for $ 10.04 + $ 
6.50 for shipping e.g. to Germany? May be this is source to consider.

73 de Karl, DK7AL

Am 03.04.2011, um 07:27:04 schrieb geoffrey mendelson:
 On Apr 2, 2011, at 3:16 PM, Woody wrote:
  Since I started back on my Drakes I couldn't find a source for
  Deoxit locally, when I found it on the net they wanted as much for
  shipping as the 5 oz can cost. I found it at  Musician's Friend for
  $14.98 and FREE shipping. I'm not plugging them just thought you
  might like a source for it and not have to pay an arm and half a leg
  to get it shipped.

 Being outside the US, I have a problem with it getting shipped here at
 all. I found a company on eBay that sells it and ships it out of the
 US. They are called PhoneKings.com and have their own website too.

 I ordered Deoxit 100 in the little tube, and they stuffed them (I
 ordered 3) in a little padded envelope so it came here in a week. If
 found that I needed fader lube too and they did not sell it alone,
 so I ordered a combination set which was on sale that week. I also
 sent them an email saying I would of preferred just the fader lube.

 They added just the fader lube to their website. My order of the
 combination packages never arrived, so I emailed them and they sent me
 a new set. That came in slightly over a week.

 Geoff.


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Re: [Drakelist] 60 meter 50 watt equivalent from a dipole

[Jim Shorney]

On Sat, 02 Apr 2011 20:58:44 -0400, roncasa wrote:

I always understood tweaking to mean maximize or peak;
Did you mean detune or something to that effect?

http://dictionary.reference.com/browse/tweak

3. to make a minor adjustment to: to tweak a computer program.
–noun
4. an act or instance of tweaking; a sharp, twisting pull or jerk.

73

-Jim


--
Ham Radio NU0C
Lincoln, Nebraska, U.S.S.A.
TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, 
HyGain 3750, IBM PS/2 - all vintage, all the time!

Give a man a URL, and he will learn for an hour; teach him to Google, and he 
will learn for a lifetime.

HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/
http://incolor.inetnebr.com/jshorney
http://www.nebraskaghosts.org



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[Drakelist] R4C CW filter for sale

[George Rybicki]

R4C 500khz CW filter $45 + $5 s/h.

Thanks

George K4MLB

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Re: [Drakelist] Testing Caps for Leakage

[Dennis Monticelli]

Richard,

Any readily detectable leakage is too much for a grid coupling cap IMO.  A
cap that even partially closes the eye on the 1uA setting of my Heathkit is
grounds for replacement.  Modern caps are cheap and easy to obtain.  If you
don't like the bright colors of new axial caps, just slip a little heat
shrink over them and viola you have a mini black beauty :-)

Dennis AE6C

On Sun, Apr 3, 2011 at 5:43 AM, Richard Knoppow 1oldle...@ix.netcom.comwrote:


  -Original Message-
 From: Dennis Monticelli
 Sent: Apr 3, 2011 1:22 AM
 To: Richard Knoppow 1oldle...@ix.netcom.com
 Cc: Drake List
 Subject: Re: [Drakelist] Testing Caps for Leakage

 Richard,

 That is very true.  Paper caps can leak yet look OK for capacitance and not
 too bad for ESR.  I think 5uA is too high for a paper cap.  If that cap is
 being used for plate to grid coupling and the grid circuit is 1 Mohm, there
 will obviously be a problem.

 I have a common Heathkit IT-11 cap tester and I've calibrated the eye
 closures for 1uA/10uA/1mA respectively on the leakage switch.  It tests caps
 just fine and will form electrolytics.

 Dennis AE6C

  I don't remember where I got the 5 uA value, you could well be right.
 It doesn't take much leakage to cause problems with coupling caps. Modern
 film caps have leakage so low its difficult to detect.



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[Drakelist] 2B Problems

[rhulett1]

My 2B suddenly quit this afternoon.  Calibrator heard on 80M, weakly on 40M, 
nothing above 40M. Audio hiss on all bands.  Ideas? 



73, Curt KB5JO 
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Re: [Drakelist] 2B Problems

[Ryan Scott]

Wiggle the crystals in the back.  I pulled my out of storage for a year and
had nothing on 40.  I wiggled the crystal and it came back to life.  I then
put some de-ox on the sockets.

Ryan N7QJ



On Sun, Apr 3, 2011 at 11:58 AM, rhule...@comcast.net wrote:

  My 2B suddenly quit this afternoon.  Calibrator heard on 80M, weakly on
 40M, nothing above 40M. Audio hiss on all bands.  Ideas?



 73, Curt KB5JO

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-- 
Ryan P. Scott
n...@arrl.net
503-880-1214
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[Drakelist] need a ac-4

[yash]

 Anyone have a AC-4 supply. Plan to rebuild the supply with heathkit shop board 
and parts. Will consider all as long as the transformer is good.
thanks
dale wt4t

please contact me off list.  y...@aol.com

 


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Re: [Drakelist] Fwd: My R-4B audio?

[kc9cdt]

Garey, Mike others as well,
The saga continues...
I lifted the lead of the Q7 base coupling cap ( the .1) and even tried 
a new one of .1 and ,47..


Q7 voltages are:

Base = .5v
Emitter =  0v ( .003)
Collector = 18.5v  IS IT SUPPOSD TO BE THAT HIGH?? Don't think so.

Audio at 12:00 id just ok , not loud and distorts at 3:00 but not super 
loud either.


Open for ideas. Thanks for all the help...I want to fix this baby...as 
it sure hears well now that I have done the full alignment.

73,
Lee






-Original Message-
From: Garey Barrell k4...@mindspring.com
To: drakelist Drakelist@zerobeat.net
Sent: Sun, Apr 3, 2011 11:07 am
Subject: Re: [Drakelist] Fwd: My R-4B audio?


Lee -

Mike has the answer.  A leaky 0.1 uF coupling cap is the only, (also
least likely!,) thing left.  I wondered about that last night, but the
resistor was more likely, even a cracked solder joint!  :-)  Being 
right

up against R137 doesn't help either.

Easy to check, just disconnect one end and see if the Q7 voltages go
where they should be.

I would replace it with one of the Panasonic metalized polyester film
caps rather than a ceramic.  It will actually be smaller than the
ceramic, and a much better audio cap.

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
www.k4oah.com


Mike Millen wrote:

Garey Barrell wrote:

Lee -

OK.  You need to measure resistor R131.  Q7 is NOT turned on at all,
there is no current through it.

The middle lead is the Collector, not the Base.  So the Base is 0.46
which isn't enough.   The Collector is 18V, indicating that there is
NO current through R148.  I suspect either R131 has way up in value,
or there is a cracked or rosin solder joint in that area.


I had the same problem  assumed Q7 had failed.

After changing Q7 with no improvement I determined that the only part
left that would explain the fault
was a leaky C167, a 100nF ceramic.

It looked fine, but fitting a new one brought everything back to
normal. (It was leaking away the bias from R131)

It's pretty unusual, but ceramics can go leaky, too.

73,
Mike



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Re: [Drakelist] Testing Caps for Leakage

[Paul Gerhardt]

Dennis
Thanks for your posting on the cap testing.  I have no idea what my
older C-3 does for leakage tests but I found this interesting paper on
it...

http://www.kb2ljj.com/Manuals/37-Heath%20Kit/Heathkit%20C-3%20%5Bnotes%5D%20WW.pdf

It sounds like the C3 is supposedly set for 4.5 ma

I may try the restoration that is suggested in the paper...

Several more new caps on order for the R4B.  I replaced the bias
filter cap for the AVC/Mute circuit that had excessive leakage and it
fixed it fine.  The C-3 did show leakage but I am still learning how
to use it and a more sensitive leakage test would be useful for audio
coupling caps.

It sounds like the sensitivity of the C-3 meter could be increased
with use of the notes by w7EKB

Paul
K3PG
http://pgerhardt.blogspot.com

Message: 4
Date: Sun, 3 Apr 2011 11:31:24 -0700
From: Dennis Monticelli dennis.montice...@gmail.com
To: Richard Knoppow 1oldle...@ix.netcom.com
Cc: drakelist@zerobeat.net
Subject: Re: [Drakelist] Testing Caps for Leakage
Message-ID: BANLkTi=34a_6copu05uz7r4m4vrzr8x...@mail.gmail.com
Content-Type: text/plain; charset=iso-8859-1

Richard,

Any readily detectable leakage is too much for a grid coupling cap IMO.  A
cap that even partially closes the eye on the 1uA setting of my Heathkit is
grounds for replacement.  Modern caps are cheap and easy to obtain.  If you
don't like the bright colors of new axial caps, just slip a little heat
shrink over them and viola you have a mini black beauty :-)

Dennis AE6C

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