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Old 29th February 2012, 09:23 PM   #1
Obrien is offline Obrien  United States
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Default Scott 355 Tuner-Preamp

Does anyone have a voltage chart or resistance chart for the Scott 355 Tuner-Preamp?
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Old 29th February 2012, 09:47 PM   #2
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Here's the schematic. It has voltages marked on it. A little hard to read, but enlarging it 200% helps.
http://hhscott.com/pdf/355.pdf
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Old 29th February 2012, 11:32 PM   #3
Obrien is offline Obrien  United States
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Default voltages for Scott 355

Thanks. I was trying to avoid making a voltage chart by hand from that schematic (I agree, it's hard to read), but I think that is the best option. Thanks for the reply.
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Old 10th April 2015, 08:34 PM   #4
Obrien is offline Obrien  United States
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I'm working on my scott 355 again... made a voltage chart from the schematic. Now I have a specific question for anyone familiar with the 355.

V503 pins 2 and 7 show a voltage required of 17.5vdc but I only measure about 8vdc... of by 50%. Does anyone have thoughts on this?

Thanks. Joe
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Old 10th April 2015, 11:24 PM   #5
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Quote:
Originally Posted by Obrien View Post
I'm working on my scott 355 again... made a voltage chart from the schematic. Now I have a specific question for anyone familiar with the 355.

V503 pins 2 and 7 show a voltage required of 17.5vdc but I only measure about 8vdc... of by 50%. Does anyone have thoughts on this?

Thanks. Joe
You are loading it down with your meter's input impedance (input resistance) forming a voltage divider with the 4.7megaohm resistor. That's to be expected. Notice that the voltages were measured with a VTVM (vacuum tube volt meter), which has a very high input resistance. Measure your plate and cathode voltages (low impedance). If they're in the ballpark, you should be okay.

You will need a scope, FM stereo signal generatior and other assorted test equipment to adjust the balance and separation pots in the MPX section.

Last edited by cogsncogs; 10th April 2015 at 11:33 PM.
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Old 11th April 2015, 12:33 AM   #6
Obrien is offline Obrien  United States
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Thanks for the info. the plate and cathode voltages are within the 10% range. I have tried to find out why I can't get stereo separation no matter how I make the adjustments. I do have a scope, mpx generator, etc. It must be my technique. So, I decided to remeasure all points in the radio to see if I missed something that is out of tolerance.

Very frustrating. Have you aligned a 355 or similar tuner?

Thanks. Joe
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