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Looking to replace Germanium power transistors with Silicon or MosFET

I figure this could work for upgrading old jukebox amplifiers, type AB or B class, from the mid 70s that ran on Germanium transistors - almost unobtanium these days. And never that reliable to begin with.

Is it possible to use MosFets to replace them? There is a bit of info on line about replacing G with S, but I don't think I've seen anyone talk about Mos...

The original amp runs on -46VDC to ground and is roughly 25W RMS into a

16R load - has an output transformer for 70V operation as well as taps for various speaker volumes. I suspect I'd have to replace the entire power amp side as mixing G with Mos is probably just not going to work.

Suggestions welcome!

Thanks!

John :-#)#

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Reply to
John Robertson
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The usual AB bias for audio amplifiers requires diodes that match the transistors' thermal character, SO either you have to buy oddball (sometimes called 'stabistor' ) biasing diodes that connect to the transistor heatsinks, OR you buy a module, prebuilt and mounted for heatsinking.

Something like this module

will save you time and money over trying to do a replacement at the component level.

Reply to
whit3rd

The differences between Ge & Si go further than just bias voltage. You could try it but don't get too excited, some amps simply won't fly with Si.

Russia still puts out lots of geraniums, don't know what power devices they have but I expect you'd find something usable. Prices are good. In extremis you could probably parallel a bank of small trannies with sharing resistors.

FET require much larger input voltage swings.

NT

Reply to
tabbypurr

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