Dick -
Is this a 'new' transceiver to you? Has it ever worked on 20M to your
knowledge? 20M is one of the 'simple' bands, (the other one is 80M,)
where Q1, Q2, V1 and V3a are not used at all.
What brand are the final tubes? Are they the same brand?
It sounds like the PA is oscillating. The most common cause is
off-brand or mis-matched final tubes. Next is improper neutralization.
Next would be a bad bypass cap. There is also a possibility with the
TR-4 series of mistuned bandpass transformers. You could remove the PA
tubes, or just remove the screen voltage at the third feedthrough from
the back on the PA shield under the chassis (C75). Careful, the second
one from the back is the HV! Once the PA is disabled, see if you have a
correct 20M signal out of the Driver stage (V6).
I suspect if you checked your '20M output', you'd find that it's NOT
where you think it is. Does the output peak with the RF TUNE control in
approximately the correct place? IF you listen on a separate receiver,
is there a signal where the transceiver dial says it is?
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-B, C-Line&
TR-4/C Service Supplement CDs
<www.k4oah.com>
Dick KF4NS wrote:
I sure hope I am not making a nuisance of myself but I am out of ideas
and have tried everything that was suggested, including neutralization
(which was ok) and have read the manuals for service and owners over
and over for hours, and have studied the schematic for hours and
hours.
The original message was for a trouble just trying to set the bias
which was fine on all bands but 20M. Since then, I have tried to tune
up in the X-CW position and all bands tuned fine except for 20M.
On 20M I can get a power out of 150W but the plate current is 600ma,
the xmit gain dips the plate current (yes, the xmit gain!), the plate
tune cap also dips the current but output drops to nothing, the RF
tune acts like the xmit gain should.
The only real defect I did find was R53 1.5K in the plate circuit of
V11 was cooked. I replaced it.
This rig has been gone completely refurbished recently with bad tubes
replaced, all contacts cleaned and contact enhancer applied, 9mhz osc.
set right on, 100khz osc set right on. neutralization set on 10M,
resoldered the contacts on the rear wafer of bandswitch, C145
replaced, P.S. upgraded to AC4R.
Keep in mind, ALL BANDS RECEIVE FINE AND TRANSMIT FINE except 20M.
Please help, Thanks and 73, Dick KF4NS
St Petersburg, FL 33714 USA
Keep The Glow!
----- Original Message -----
From: "Dick KF4NS"<[email protected]>
To: "DrakeRadio list"<[email protected]>;
<[email protected]>
Sent: Monday, October 04, 2010 6:09 PM
Subject: TR4C weird xmit trouble
Ok guys, I have this black cloud over me right now. The radio is
receiving fine (other than the filter defect) and I decided to get
the
xmit completely checked out before I wrap it up.
All of a sudden while on 20M band position and checking the PS bias,
it jumps intermittently to 400-600ma with no drive, sideband switch
in
ccw position (actually makes no difference), dummy load connected
and
no mic or key connected.
After quite a few hours pulling out my hair (just the gray ones) I
tweaked the TUNE control and the trouble went away. I tried full ccw
and cw and everything in-between on all the other bands and no
effect, only affects 20M and only when the TUNE control is between 1
and 6. I checked and rechecked the band switch contacts over and
over.
What the heck, I even tapped all the tubes and every other silly
thing. Given time and a few cups of coffee I can usually make sense
of
these kind of things but not this time. HELLLLLP!!
73, Dick KF4NS
St Petersburg, FL 33714 USA
Keep The Glow!
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