[Drake] TR4C unwanted carrier

[WQ9E at btsnetworks.net]

Dick,

Did you try to re-balance the balanced modulator as the carrier increased?  There could be a bad component in this circuit that changes significantly with temperature.  Some diodes shift characteristics as they age making them far more temperature sensitive but the most likely suspect is a resistor and the carrier balance pot would be my prime suspect.

The other thought is to listen to the 9 Mhz. oscillator with a stable external receiver and see if it is changing frequency over time and/or as the heat increases.

A soldering iron close to suspect components will help you to identify the guilty party.

Rodger WQ9E

----------------------------------------
From: "Dick KF4NS" <kf4nsradio at verizon.net>
Sent: Tuesday, February 08, 2011 4:10 PM
To: "Drake list at mailman" <drake at mailman.qth.net>
Subject: [Drake] TR4C unwanted carrier 

Hi Guys,
This is a repost of the one I sent over the holidays. Must have been a 
bad time to send it. Got no replies.

"I just had my first lengthy QSO on 20M SSB since the restoration. A
problem has popped up that was not an apparent trouble while doing all
the testing on the bench.

After about a full minute of transmission the wattmeter starts showing
a gradual climbing of carrier on the SSB signal. I have very good air
flow, carrier balance was set during rehab, the finals were
neutralized. Power output is over 200W with plate current reading
around 500ma.

This does sound like a heat problem but as I said, there is plenty of
air flow in and out of the rig. I have not tried lowering the output
yet to see what that does but just wanted to put this to the groups
ASAP before I do any damage. I know that one of the filters is bad but
the 9mhz OSC. was tweaked with C130 to a satisfactory balance which
left the CXR OSC still very close to 9MHZ. Let me know your thoughts."

73, Dick KF4NS
St Petersburg, FL 33714 USA

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