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>
To: "Donley" <donley...@comcast.net>
Cc: "Drakelist" <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>
To: "Donley" <donley...@comcast.net>
Cc: "Drakelist" <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
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