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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