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Old 14th March 2012, 09:28 PM   #1
Trout is offline Trout  United States
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Default Magnatone #210 Power Stage

I was just looking over this amp for restoration and found very little documentation other than a rough hand drawn schematic.

Anyway, I thought someone might be interested in this power section. Oddly rather than directly grounding the cathode & bypass cap on the power tube, they route it through the speaker/ot secondary?

Can someone give me any insight as to what the influences of this might be?

See picture.
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Old 15th March 2012, 01:32 AM   #2
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It's a form of negative feedback. You'll see it in some HiFi amps. If they are push pull, the 4 ohm tap will be grounded, the common terminal goes to one tube and the 16 ohm tap goes to the other. Before you ask, the 4 ohm tap is the center tap of a 4, 8, 16 ohm output transformer. Do the math, it takes twice as much voltage to make the same power in 16 ohms as it does for 4 ohms. There is a mod for the Dynakit Stereo 70 that uses this.
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Old 15th March 2012, 03:14 AM   #3
Trout is offline Trout  United States
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Quote:
Originally Posted by Loudthud View Post
It's a form of negative feedback. You'll see it in some HiFi amps. If they are push pull, the 4 ohm tap will be grounded, the common terminal goes to one tube and the 16 ohm tap goes to the other. Before you ask, the 4 ohm tap is the center tap of a 4, 8, 16 ohm output transformer. Do the math, it takes twice as much voltage to make the same power in 16 ohms as it does for 4 ohms. There is a mod for the Dynakit Stereo 70 that uses this.
OK, That makes sense,

This is just a simple 4-5W SE amp, no extra taps, but I assume the concept is still the same.
First time I have ever seen this in a guitar amp.
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Old 24th March 2012, 08:16 PM   #4
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I just got one of these a couple of weeks ago and have only seen the same schematic. If anyone has an alternate schematic, I would like to see how accurate the hand-drawn one is.

Mine needed re-tensioning the tube socket inserts and that's all. It seems to be all original and it's from '61. Surprisingly, it doesn't hum or hiss- even the caps are OEM but I plan to replace those ASAP. I would like to replace the speaker with something that can handle a bit more but I don't think I want more sensitivity- it's loud enough as it is.

I had a BF Vibro Champ and this smokes that one, even though this only has a 6" speaker. The vibrato is great and it breaks up really nicely.
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