Silvertone 1451 -Mystery adjustable cap - diyAudio
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Old 30th August 2013, 08:56 PM   #1
jjman is offline jjman  United States
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Default Silvertone 1451 -Mystery adjustable cap

Picked up this little beast on ebay. Yes I have ordered an iso tranny and other stuff.

What is the function of that adjustable cap?

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Old 30th August 2013, 11:11 PM   #2
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I would think it is to reduce high frequency gain to kill ultrasonic oscillations.
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Old 30th August 2013, 11:20 PM   #3
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The variable capacitor seems to increase any mains born interference from the cathode of the main rectifier to the screen grid of the 1st stage amplifier.
In other words, not a lot!
I should think it makes a better spark gap.
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Old 30th August 2013, 11:51 PM   #4
kevinkr is offline kevinkr  United States
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Ripple (buzz) canceling.
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Old 10th November 2013, 06:00 PM   #5
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I have a 99% identical Airline 8511 amp, even down to layout, and the cap does nothing for me except change the 60 Hz tone from a buzz to a hum to a rumble, its very odd and I am surprised that on the cheapest amps made by these companies, they included an expensive variable cap solely for this, when they couldn't even afford a tone knob... lolClick the image to open in full size.Click the image to open in full size.Click the image to open in full size.
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Old 11th November 2013, 01:28 AM   #6
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Quote:
Originally Posted by kevinkr View Post
Ripple (buzz) canceling.
I'll second that.
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Old 11th November 2013, 01:45 AM   #7
eyoung is online now eyoung  United States
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replace electrolytics all of them especially the B+ caps...
probably late 40's early 50's electrolyte all dried up.

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Old 15th November 2013, 12:42 AM   #8
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Quote:
and the cap does nothing for me except change the 60 Hz tone from a buzz to a hum to a rumble
The electrolytics of the day were pretty useless for filtering out high frequency noise. Try plugging in an electric drill that uses a motor with brushes into the same outlet as the amp. Pull the trigger on the drill and tune the cap for minimum scream! Brushed motors were a lot more common back then. Amps with power transformers were more immune to this noise.

I had an old amp back in the 60's that picked up my mother's vacuum cleaner in the other end of the house. It was a 4 tube design without a power transformer. Fortunately it didn't survive my hot rodding experiments.

Quote:
they included an expensive variable cap solely for this
This type of cap was common in the IF cans of old radios. They weren't all that expensive when bought by the 10,000 piece lot.
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Old 15th November 2013, 12:50 AM   #9
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So the only purpose of this little cap is to reduce noise on the AC line, kind of like a death cap would on a fender, only even more pointless? And yes, of course the electrolytics are replaced...
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Old 15th November 2013, 01:10 PM   #10
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Can anyone tell me the idea behind omitting the mains transformer? Just to get the user closer to Darwin's award?

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