SB 200 on 6M

[Paula Uscian]

Looking for some troubleshooting tips on the following. I have an SB 200 that had been converted and used successfully on 6M but still can be used on the HF bands. When I acquire the amp I was told it was arcing. It loaded on 6M when I first fired it up but something emitted the smell of warm electrical parts, and in fact some of the resistors in the parasitic chokes were darkened or had failed.

I replaced these chokes using 2 sets of 3 x 150 ohm 2 watt carbon compound resistors and 2 strips of copper plate cut 85mm x10mm x1mm and bent to form a U shaped inductor (3 resistors fit as a triangular bunch in between the two ends of the U). I situated these chokes as much as possible at right angles to each other to avoid interaction between them. My first effort resulted in one of the resistors failing very quickly. I remade that choke, reintalled/reoriented both and retested.
 
The amp has a Standby/Operate rocker switch in addition to an on-off switch. When the amp is on and I'm in Standby, both the amp meter and an outboard SWR bridge register the exciter drive power. However when I switch to Operate, while I hear the relay clicking, I get no power reading at all--not even the power from the exciter/transceiver, let alone any amplification. I tried this first on 6M and then on 20M where the heat wouldn't build up as quickly--same results on both bands.
 
Any ideas as to what else may have failed or what else I can check to determine why I no longer get anything coming out of the amp in operate mode? Seems something must be open in the Operate circuit but not sure where to start looking. Thanks for any help or ideas!
 
73 Paula k9ir

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