Screen Dropper Resistors?

Get support and show off your MetroAmp 50 Watt kit builds.

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revolver1
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Screen Dropper Resistors?

Post by revolver1 » Wed Oct 18, 2017 3:34 am

I'll be using the 1202-118 power transformer and the 784-139 output transformer.

So I think the PT's B+ is speced at 420v, would this be correct to use 2x 8.2k resistors for the dropper?

As I understand it the higher the resistance the less voltage gets through and therefore the browner the sound.

Inversely the less resistance the more voltage passes and so more power stage head room is created.

So it's all about how much B+ is produced and getting it in the zone. So this is the bit I'm not 100% on. Is this right

450v use 2x 10k
420v use 2x 8.2k
380-390v use 1x 10k

Ultimately what B+ should I be shooting for on a 68/69 50w 1987?

Roe
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Re: Screen Dropper Resistors?

Post by Roe » Wed Oct 18, 2017 4:15 pm

try it and see what you like. it drops the preamp, not the screens
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revolver1
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Re: Screen Dropper Resistors?

Post by revolver1 » Thu Oct 19, 2017 2:05 am

Ok, thanks Roe. But isn't there a target voltage range Marshall would have been looking to hit for these amps?

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