"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" <[email protected]>
To: "Donley" <[email protected]>
Cc: "Drakelist" <[email protected]>
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
[email protected]
http://mailman.zerobeat.net/mailman/listinfo/drakelist
