BIAS yeah I don't know..

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Reeltarded
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BIAS yeah I don't know..

Post by Reeltarded »

Recapped a '61 Bandmaster head. The amp used to rock 25 years ago when I put it up.

So looking around inside I see tied off 5v taps, and the death cap, and there are a couple wires moved and someone rebuilt the bias board with MF resistors and 20/20-50v bias pair. I am going to use 50u-50v bias caps and swap tubes.

So.. it's not adjustable. Where to measure and what to expect?

:)

It just supposedta work? Really?
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cbass
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Re: BIAS yeah I don't know..

Post by cbass »

After you make sure your bias voltage is reasonable.
Measure the resistance between your Ot primary legs to the ct .then turn the amp on and measure the voltage drop where you just measured resistance. Divede volts/ohms boom plate current.

I would use 100 volt caps
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Reeltarded
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Re: BIAS yeah I don't know..

Post by Reeltarded »

Why, because you have some? :)

I only have 50v caps.

Thanks buddy.
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cbass
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Re: BIAS yeah I don't know..

Post by cbass »

I would use more than 50v rated caps cause your probably going to be close to 50v to bias the thing.but then again im not badass like you
Firestorm
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Re: BIAS yeah I don't know..

Post by Firestorm »

Originals were supposed to be 8u-150. Schematic shows - 55V at the grids. The first cap will see more than that.
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Structo
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Re: BIAS yeah I don't know..

Post by Structo »

A good spec for the bias cap is 100v/ 100uF

Miles, do you know which circuit this amp actually is?

I'm sure you know volumes more than I will ever know.

It is amazing how much the power supply can affect the way they sound and behave.
Tom

Don't let that smoke out!
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Reeltarded
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Re: BIAS yeah I don't know..

Post by Reeltarded »

I don't have the caps I need on hand.

It is 6g7-a on the chart but doesn't match any schematic perfectly ;)

I had myself confused because I swapped headboxes on a couple of these to match an oxblood 2x12 but I think this one is actually 62-3 and not the amp I thought it was.

I am going to shorten the power cable then bring it up on the variac to see if it gives a crap or just craps.
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jelle
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Re: BIAS yeah I don't know..

Post by jelle »

send me your address and I will send you two 160v 47uf caps.
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Re: BIAS yeah I don't know..

Post by Reeltarded »

I love you to death and thanks for the awesome offer but I can just add them to another order tomorrow. :)

Had a 15A FB fuse haha

This is definately the other head. I sold the one I wanted to keep!! Damnit!
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jelle
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Re: BIAS yeah I don't know..

Post by jelle »

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Reeltarded
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Re: BIAS yeah I don't know..

Post by Reeltarded »

BOOP! Found a drawer where I stick stuff so I won't lose it FULL of 10u160v!

Now if I can remember where I put the fuses...
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jelle
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Re: BIAS yeah I don't know..

Post by jelle »

Duh!! fuses are easy...
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Reeltarded
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Re: BIAS yeah I don't know..

Post by Reeltarded »

hahaha I have a 1640v one and a 4600v one on hand.

Hammer and a railroad spike.
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