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 Post subject: Seeburg 200LU-3, with PA5 preamp. AVC trouble
PostPosted: Sep Sun 12, 2021 4:39 am 
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Joined: Mar Tue 03, 2009 11:12 pm
Posts: 2024
Location: Great Bend KS
Have this old thing working perfectly mechanical wise, but when ever you turn on the AVC the sound goes dead. I do have the service manual but am having a hard time figuring out how the avc circuit works. I've changed all the electrolytics in this very hard to service tiny preamp chassis! Plus, being a tube circuit, loaded with very high value resistors that check pretty close to stated values. The tube voltages are close also. Tubes check ok on tube tester. I'm a bit puzzled on the squelch and mute circuits and can't understand the 6BJ6 and 12AX7 tube operation. Service manual gives a couple of sentences on how the circuit works, but I need a couple of paragraphs at least!


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 Post subject: Re: Seeburg 200LU-3, with PA5 preamp. AVC trouble
PostPosted: Sep Tue 14, 2021 7:16 pm 
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Joined: Nov Sun 29, 2020 5:59 pm
Posts: 300
Location: Northeast Illinois 60188
Steve, you might get a better response of you could post the schematic and whatever associated service info that you have here for reference.


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 Post subject: Re: Seeburg 200LU-3, with PA5 preamp. AVC trouble
PostPosted: Sep Wed 15, 2021 3:51 pm 
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Joined: Jan Wed 11, 2017 3:24 am
Posts: 6
Location: Terrell, Texas
Steve,
I'm shooting in the dark here as I don't have a schematic, but I know the Seeburg amps from the C (MRA3) to the VL200 (HFMA1) use a cap from the plate of the AVC tube to the grid of the second audio stage. If that leaks at all, it'll bias the stage way down, causing your symptom.
If there is a cap from Pin 5 of the 6BJ6 to either Pin 2 or 7 of the 12AX7, change it. It was .06 mfd on the amps I worked on.

I hope this helps.
Bill


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 Post subject: Re: Seeburg 200LU-3, with PA5 preamp. AVC trouble
PostPosted: Sep Wed 15, 2021 10:04 pm 
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Joined: Mar Tue 03, 2009 11:12 pm
Posts: 2024
Location: Great Bend KS
Thanks Audiophone, you gave me a couple things to try. The schematic I have is in the paper service manual, not online where I can copy and paste. Have no idea on how to get a picture of the schematic from my manual to my computer! I do have a scanner, maybe I can figure out how to do that. Thanks again! This preamp chassis is so compact with parts really crammed in there!


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 Post subject: Re: Seeburg 200LU-3, with PA5 preamp. AVC trouble
PostPosted: Sep Sat 18, 2021 2:54 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 10853
Location: Beaver Falls, PA. USA
In the 1950s, Seeburg used a lot of CD "Tiny Chief" and John Fast molded capacitors, and they will all be leaky by now. Some of their amps are fairly hard to work on, due to the tightly packed chassis.

_________________
Tim KA3JRT


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