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
_______________________________________________
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist
