[Drake] TR4C unwanted carrier

[Joe Wheeler]

I saw a situation once where the driver tube, I believe a 12BY7 was 
going into self oscillation.
k5jw

On 2/8/2011 4:30 PM, WQ9E at btsnetworks.net wrote:
> 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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