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 Post subject: 6GY6 two tube transmitter problem
PostPosted: Jan Wed 10, 2018 3:49 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 18593
Location: Warner Robins, GA
I have a 6GY6 two tube transmitter that works great except for one issue.

I installed an Edcor WSM 15K/15K balanced/unbalanced to balanced/unbalanced transformer so that I could isolate the input audio ground from the circuit ground which solved a hum issue that would vary based on what was connected to the audio input and also so that I could run a balanced audio line to the transmitter from my pro audio mixer if so desired.

Now for my RCA K-80 console the ground lift switch on the transmitter has to be set to connected for the least hum, although with my Collins R-390 it has to be set to lift for least hum.

When I set the switch to connected and I plug in a source if I turn up the audio level control on the transmitter to 3/4 CW rotation I get an indication on the VU meter with no audio signal present. I'm thinking it is some sort of oscillation, but I am not sure what is causing the issue.

Before I break out the scope and start troubleshooting are there any obvious things that stand out?

Will have to get the schematic when I go back to work tomorrow and post the part showing the transformer how it connects.


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 Post subject: Re: 6GY6 two tube transmitter problem
PostPosted: Mar Tue 27, 2018 1:20 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 18593
Location: Warner Robins, GA
I found the problem.

Given the transmitter is near the amp for the subwoofer in my stereo and I was right by the amp I switched it off because I'm lazy and it was so close.

The problem went away completely.

Not sure if it is the switch mode power supply the BASH 500 watt amp uses or if it is something with the ground or perhaps it has to do with the amp not having its own ground connection in the IEC plug.

Also given I added a buffer to my McIntosh C-24 preamp on the record out jacks I plan on modding the transmitter with a second Edcor WSM transformer so it has a stereo input again so I can feed it from one of the processor outputs of the DBX 200 program route selector.

I had been feeding it from the center channel output of the C-24, but that involved turning the subwoofer amp off and the main speakers amp off.

Now all I need do is press a button and the audio is routed to the transmitter only.


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