I was getting strange output variations when I had leaky driver transistors on
the PA deck. Easy to check, the base voltage on the drivers should be zero in
RX. If it's anywhere near 0.6V, there's a problem. When I lifted the base
leads, one of them floated right up to 13.8V. Be careful not to short the base
to the collector when you measure, you will destroy the device instantly.

A similar problem that I have now is a dirty bandswitch. Depending on the band,
I often have to wiggle and jiggle it to get proper output. It's due to hit the
bench soon for another project, so I'm going to DeOxit the band switch at that



On Tue, 4 Mar 2014 07:35:19 -0700, J. Steven Cochrane wrote:

>I have run out of ideas. One of my TR7s has intermittent output power 
>problems. Sometimes there is no output, sometimes there is 40 to 10 watts 
>output depending on band and sometimes there is full output.
>When I change bands there usually is no output as well as low receive 
>sensitivity. When I tap the PTT button on the mic the receive comes up to 
>normal and I usually get 40 to 20 watts (CW) out on transmit. Sometimes when 
>I push on the High Pass Filter section boards I get full output, sometimes I 
>don't. Sometimes I get full output when talking into the mic (with the PTT 
>button depressed of course) and not doing anything else. I searched the 
>archives with little luck.
>What I have done so far:
>1. Pulled all the boards and reseated them (some numerous times).
>2. Loosened and tightened all screws I could get to, externally and 
>3. Cleaned all switches at least twice.
>4. Pulled the power supply board and replaced C2108.
>5. Readjusted 10 volt supply and checked Fixed pass band adjustment (all 
>6. Checked 40, 13.695, and 8.05 Oscillators (all Good)
>7. Attempted to do Transmitter Alignment and ALC Adjustment but with only 
>intermittent power output it was hit-and-miss at best.
>8. Disconnected Diode CR1402 on the High Pass Filter Board (no change).
>9. Checked 10 Volt transmit voltage on Parent Board when in transmit (right 
>on 10 Volts).
>10. Changed out the T/R relay twice ( no change).
>11. Changed cables and dummy load (no change).
>12. Cussed a lot (didn't help).
>Any ideas where to go next other than crazy?
>Steve W7JSC 
>Drakelist mailing list

“There’s something out of place – let’s go and poke it with a stick.” – The 
Doctor, "Amy’s Choice"

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