Garey,
Thanks for the clarification. As always, you are the source!
As for the floating K, I think it's normal when the mode switch is in the SSB position and the
PTT is not pressed. I know you wanted Richard to measure the voltage during TX, but I think he
measured it while not transmitting (i.e. ptt not pressed). To me the problem seems that the
final tubes stays cutoff within the bias voltage range provided by the AC-4. I thought it was
the screen voltage issue, but again I am relatively new to this hollow state technology so it
was just a guess.
Kihwal, K9SUL
----------------------------------------------------------------------------------------------------
*From:* Garey Barrell <k4...@mindspring.com>
*To:* drakelist <Drakelist@zerobeat.net>
*Sent:* Tuesday, July 12, 2011 12:57 PM
*Subject:* Re: [Drakelist] TR-4C Bias Adjustment
Kihwal -
I agree with most of what you said. The Screen voltage is slightly low, most likely as a
result of leakage in the AC-4 filter caps. But I do NOT believe it has any significant effect
on this problem as he is able to get full power in the X-CW position.
You are correct on the X-CW shifting the Carrier Osc (via relay K2) so that the CARRIER signal
will go through one of the filters. This configuration is used for both tune-up and CW
operation. The SIDETONE is NOT used for this purpose in the TR-4C, only to operate the VOX
circuit.
In the T-4XC, the CO is shifted for CW operation. However, in TUNE mode the SIDETONE IS
applied to the Balanced Modulator, generating a single tone SSB signal, and the CO is NOT shifted.
The key here is that these Cathodes are NOT grounded in either SSB position. I believe that is
the result of the PTT/VOX circuit NOT pulling in the relay in that switch position. Grounding
the tip of the MIC connector causes the relay to pull in, and I believe that will cause the PA
Cathodes to read the correct near zero reading rather than the 156 VDC he measured. The PLATE
meter should then read correctly. We'll see! :-)
I'm now thinking the problem is in the VOX circuitry.
73, Garey - K4OAH
Glen Allen, VA
Kihwal Lee wrote:
> Richard,
>
> I think you need to find the cause of the low voltage (230V vs. > 250-260V)
and fix that first.
> The meter circuit does not change by switching the sideband. As Garey > said
it's only
> job is to choose the filter and the lamp.
>
> The low screen voltage will certainly affect the plate current.
>
> In the X-CW mode, the carrier frequency is shifted and the side-tone > is fed
to the balanced
> modulator. Correct me if I am wrong, but my understanding is that > since the carrier is
shifted,
> this signal can only pass through the filter selected at the X > position. At the non-X
position,
> no signal goes through.
>
> A lower screen voltage negatively affects the plate current. A lighter > bias
may be required,
> but AC-4 may not be able to supply it. Now, even in this case, if you > push signal to the
control
> grid, there will be some plate current. By advancing the TX gain, you > did
exactly that. But
> as you know that's not the idling current (we are providing input) we > want
to check when
> setting the bias.
>
> If the screen voltage is not too low, you can still see a good power > output. But without
proper
> biasing, the linearity will suffer.
>
> Kihwal, K9SUL
>
>
>
----------------------------------------------------------------------------------------------------
> *From:* Donley <donley...@comcast.net <mailto:donley...@comcast.net>>
> *To:* k4...@mindspring.com <mailto:k4...@mindspring.com>; drakelist >
<Drakelist@zerobeat.net
<mailto:Drakelist@zerobeat.net>>
> *Sent:* Tuesday, July 12, 2011 10:57 AM
> *Subject:* Re: [Drakelist] TR-4C Bias Adjustment
>
> Garey,
> Sorry about the delay in my response. Time gets away from me.
>
> I acquired the TR-4C several years ago and my normal procedure is to > put a
new acquisition on
the bench and run it through a simple use test. Then I tag it with the information, working or
not, and put it on the shelf for later free time. This one has no tag, so my procedure must
have failed. I don't remember if the bias worked or not. My guess is not.
>
> Yes, the receiver works just fine. The RV-4C is on the shelf, not >
connected. VOX and ANTI-VOX
are set at mid-range.
> The transmitter works fine also, I just can't measure the bias > current. Can
I assume that the
bias current is close to 100 mA if the bias voltage is ~ -60 VDC? It seems like there must be
an open in the meter circuit when switched to set the bias. That should involve switches and
relay contacts in the circuit. I am not very good at tracing circuits on the schematic when
they start running through switches.
> In SSB mode, NON-X position, grounding the 'TIP' MIC connector pulls > in the
relay.
>
> I should probably order a new relay and try it, but the old one > appeared to
work when I had it
out and open for cleaning. One set of contacts was somewhat dirty but I had good continuity
after cleaning.
>
> Richard
>
>
>
>
>
> > Richard -
> >
> > Probably should have asked this question a while ago, but has this > > transmitter EVER
worked,
to your knowledge?
> >
> > Does the receiver work?? Do you have an RV-4(C) connected? Verify > > that the VOX and
ANTI-VOX
controls on the right side are about mid-range.
> >
> > Unless something has been rewired, the Cathode line of the PA should > > read that 0.3 to
0.4 VDC
ANY time the relay (the four pole one near the power connector) is energized, regardless of ANY
other switch position. The Cathode lead comes through the feedthrough cap on the PA section
shield, goes to R45 (2 ohms, on the board with the relay) and is hard wired from the other end
of R45 to the relay contact. This contact is grounded any time the relay is energized,
grounding the PA Cathodes.
> >
> > When it's in SSB, in the NON-X position, try grounding the 'TIP' of > > the MIC connector
and see
if the relay pulls in.
> >
> > 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>
> >
> >
> > Donley wrote:
> >> Garey,
> >> I replaced the 6EV7 and there was no change. The plate voltage on > >> the 6EV7 measures a
little
low at 230 VDC (supposed to 260). This makes the voltage on the relay lower than the 48 VDC
(measures about 26 V if I remember correctly, but it seems to pull in okay). I measured the
four voltages in all combinations of the sideband switch and the mode switch settings (sideband
switch in non-X position and mode switch in SSB position and then in X-CW position). Then
(sideband switch in X position and mode switch in SSB position and then X-CW position).
> >> The four plate voltage measurements were 687 to 690 VDC.
> >> The four screen voltage measurements were 230 to 236 VDC (a little > >> low if 260 is
correct).
> >> The four grid voltage measurements were around -60 VDC.
> >> When the Mode switch was in the SSB position, the cathode voltage > >> was
156 VDC for each
position of the sideband switch.
> >> When the Mode switch was in the X-CW position, the cathode voltage > >>
was 0.3 to 0.4 VDC.
> >>
> >> When I said I could adjust the bias voltage in the sideband X > >> position, I didn't tell
you
that to do that I had to advance the transmitter gain control slightly to get 100 mA. But when
I switched back to sideband non-X position, the current dropped to zero with no control by the
bias knob on the AC-4.
> >>
> >> I have pulled the one relay and opened it and cleaned the contacts > >>
with no change. Also
cleaned the contacts on the second relay.
> >>
> >> I have a power supply rebuild kit to install but the voltages > >> appear to be okay and
steady.
I should probably order a new relay and try that.
> >>
> >> If I adjust the bias pot to get -60 VDC, I have no idea what the > >> bias current is, but
I get
plenty of power out, around 200 watts, so it seems to work , I just can't
measure the current.
> >>
> >> ??
> >> Richard
> >>
> >>
> >> ----- Original Message ----- From: "Garey Barrell" > >>
<k4...@mindspring.com
<mailto:k4...@mindspring.com> <mailto:k4...@mindspring.com
<mailto:k4...@mindspring.com>>>
> >> To: "Donley" <donley...@comcast.net <mailto:donley...@comcast.net>
<mailto:donley...@comcast.net <mailto:donley...@comcast.net>>>
> >> Cc: "Drakelist" <Drakelist@zerobeat.net > >>
<mailto:Drakelist@zerobeat.net>
<mailto:Drakelist@zerobeat.net <mailto:Drakelist@zerobeat.net>>>
> >> Sent: Saturday, July 09, 2011 3:00 PM
> >> Subject: Re: [Drakelist] TR-4C Bias Adjustment
> >>
> >>
> >>> Richard -
> >>>
> >>> I've thought about this some more this afternoon, and I think the > >>> next step is to
measure
the PA voltages with the switches set per the manual and see WHAT is missing.
> >>>
> >>> There aren't that many choices, ONE or more of the three are > >>>
missing or incorrect.
> >>>
> >>> Plate +650 VDC
> >>> Screen + 260 VDC
> >>> Grid ~ -60 VDC
> >>> Cathode ~ 0 VDC
> >>>
> >>> 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>
> >>>
> >>>
> >>> Donley wrote:
> >>>> "My guess is that either a KEY is plugged in and open, or the > >>>> 'shorting' jack,
isn't! Try
just
> >>>> inserting a phone plug into the KEY jack several times to see if > >>>> that shorting
contact
will close as
> >>>> it should. Otherwise just insert a shorted phone plug into the > >>>> KEY
jack."
> >>>>
> >>>> Garey,
> >>>>
> >>>> Been there, did that. The key is not plugged in but the jack is > >>>> shorted as it
should be.
When set up according to the manual, there is no bias current indicated on the meter when
adjusting the bias control, but there is adjustable voltage (around -60 VDC +/- adjustable) on
the PA grids. If I switch the sideband back to the "X" position, there is current indicated and
I can easily vary it with the bias control and get 100 mA. What is the difference in being in
the "X" sideband or opposite sideband position? Both are done with no transmitter gain and I
get current in the "X" position and not in the other. Maybe there is an open condition on the
sideband switch when it is in the non "X" position.
> >>>>
> >>>> Question - Is the bias current just plate current with no > >>>>
transmitter gain?
> >>>>
> >>>> Thanks.
> >>>> Richard
> >>>> kc9ub
> >>>>
> >>>>
> >>>>
> >>>>
> >>>> ----- Original Message ----- From: "Garey Barrell" > >>>>
<k4...@mindspring.com
<mailto:k4...@mindspring.com> <mailto:k4...@mindspring.com
<mailto:k4...@mindspring.com>>>
> >>>> To: "Donley" <donley...@comcast.net > >>>> <mailto:donley...@comcast.net>
<mailto:donley...@comcast.net <mailto:donley...@comcast.net>>>
> >>>> Cc: "Drakelist" <Drakelist@zerobeat.net > >>>>
<mailto:Drakelist@zerobeat.net>
<mailto:Drakelist@zerobeat.net <mailto:Drakelist@zerobeat.net>>>
> >>>> Sent: Friday, July 08, 2011 11:18 PM
> >>>> Subject: Re: [Drakelist] TR-4C Bias Adjustment
> >>>>
> >>>>
> >>>>> Richard -
> >>>>>
> >>>>> I'm not sure I follow your description below.
> >>>>>
> >>>>> 1. There is only ONE metering circuit, NO switching involved. > >>>>> If it can read
PLATE
current it can also read BIAS current.
> >>>>>
> >>>>> 2. 26 V across the relay sounds low, but if it pulls in that > >>>>> can be left til
later.
> >>>>>
> >>>>> The manual says to switch the SIDEBAND switch counter-clockwise > >>>>> (the 'non-X'
position)
and the MODE switch to X-CW. I don't have a TR-4C set up at the moment, but I believe the KEY
has to be closed. IF you have a key plugged in, it must be shorted. IF you do NOT have a key
plugged in, there is a contact on the key jack that is 'supposed' to short the key. IF this
contact does not MAKE properly you would see what I think you are describing.
> >>>>>
> >>>>> The goal here is to put the transceiver into TRANSMIT mode > >>>>>
(X-CW) with the 'non' X
SIDEBAND selected and the MIC GAIN at minimum. This should register the BIAS current of the PA
stage since you're essentially in SSB with no audio applied, resulting in only the suppressed
carrier and no PLATE current.
> >>>>>
> >>>>> My guess is that either a KEY is plugged in and open, or the > >>>>> 'shorting' jack,
isn't! Try
just inserting a phone plug into the KEY jack several times to see if that shorting contact
will close as it should. Otherwise just insert a shorted phone plug into the KEY jack.
> >>>>>
> >>>>> 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>
> >>>>>
> >>>>>
> >>>>> Donley wrote:
> >>>>>> A few weeks ago I started working on putting a TR-4C back on > >>>>>> the air. I posed
a question
about the bias adjustment. I finally got back to working on the transceiver and still have some
questions. I have followed all the information that has been sent to other people with bias
problems, but that info has not helped me.
> >>>>>> My problem is that the bias current is not displayed or changed > >>>>>> on the Plate
Current
meter when I adjust the bias control. I can measure and adjust the bias voltage on the final
grids so I know the system is working, I just can't measure the current. I have done most of
the suggested things: loosen and retighten most ground screws, pulled and checked all tubes and
used Deoxit on the pins and reinserted multiple times to clean the pins and sockets and cleaned
the contacts on the relays. The 48 volt relay only has 26 volts on the pins, but it appears to
pull in okay and work. Is 26 volts normal?
> >>>>>> Using the Drake manual instructions for bias adjust, no plate > >>>>>>
current reading is
detected even though everything seems to be working. With the sideband switch in the clockwise
position (opposite what the directions say) and transmitter gain full counterclockwise, I can
adjust the plate current with the bias control. I also get full power output and can control
the plate current with tuning and loading.
> >>>>>> It seems everything is fine except being able to measure the > >>>>>> bias current
with the
recommended setup procedure.
> >>>>>> Any suggestions would be appreciated.
> >>>>>> 73
> >>>>>> Richard
> >>>>>> kc9ub
