Richard -
OK.
1. There is NO difference in the meter circuit, no switching involved for PLATE or IDLE. You are
measuring Cathode current in both conditions, just at different levels.
2. The SAME relay contacts are used to ground the PA Cathodes in both NON-X and X-CW switch
positions, again, no switches involved.
The fact that you read essentially zero volts on the PA Cathodes in all but the NON-X SSB switch
position means that the relay contacts ARE closing, and ARE good.
By the same token, the fact that you read -156 VDC on the PA Cathodes in the NON-X position means
that there can be NO Plate or IDLE current in the stage.
When you are in SSB, NON-X and ground the TIP of the MIC connector, the PA Cathode voltage should go
to near zero, just as in the other modes, and you should see IDLE current. If you speak into the
microphone, the PLATE current should increase and show RF output.
Setting the Grid bias to -60 VDC is really not a satisfactory way to set the IDLE current. You will
almost certainly end up with either too much or too little IDLE current, resulting in distortion on
SSB and/or tube damage.
You said you are able to tune up the transmitter, does the PLATE current 'dip' when the RF output is
at maximum.? What is the Plate current measured?
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,
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>
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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