Plinius III 80 watt p/c class AB Amplifier

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#41
Hi,
The output stage uses MJ15024/25 devices. the transformer has a sticker specifying 500VA, 52 volt output. I measured 73v filtered with about 18mv noise. the capacitors are elna 27000uF 80v (I've built a 50watt, single ended amp that has 188000 uF per 35v rail, now that will generate sparks!). I don't have an LCR meter that measures that high, but after nearly 30 years they could be ready for replacement. I'll test them with a load later.
 
#42
Nice big transistors. 250V, 16A. Havent seen those pupy's before. When I forst got my Plinius. One of the channels had a problem. My advice is to chect all other components (semis and resistors) as it is probably DC coupled. I found some leaky transistors in mine . Also emiter resistors worth checking/replaceing before replacement of the o/p transistors (expensive).
 
#43
Bringing this thread back from the dead!

I just saved a Plinius II, III and IV combo from the scrap pile.
A quick look in the poweramp suggests it needs a rebuild.

The preamp psu uses the same mj15003/15004 used as the poweramp outputs.

Thanks for the schematic, Butcher.
 
#44
cubastreet said:
Bringing this thread back from the dead!

I just saved a Plinius II, III and IV combo from the scrap pile.
A quick look in the poweramp suggests it needs a rebuild.

The preamp psu uses the same mj15003/15004 used as the poweramp outputs.

Thanks for the schematic, Butcher.
Click to expand...

Really from a scrap pile similar like this ??
https://www.ameslab.gov/files/imagepicker/k/kgibson/Scrap-metal-heap-copy.jpg
This is really amazing.

The use of bjt power output devices for discrete serial regulators is really nothing special. But if there is in use parallel regulators for the pre amp section, then it would be no ordinary.
Schematics would be interesting in any case.
 
#50
Has anybody already tried to play with such Triple CFP? Any simulation to show how to make it without oscillation? My first attempts are already bad at simulation level with common modern BJT...

It would be very intersting to be able to use this topology as the bias is very stable as mainly dictated by pre-driver vbe.

Any recommandation?

What is the goal of R35 R36?
 

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#51
Those Emitter resistors are there to prevent VHF (RF) oscillation by lowering HFE (gain) It is common practice with RF amplifiers. It is a way of equalization. I cant name the correct terminology but I tink I know a tin or tew!!


IT IS A PRODUCTION METHOT OF MATCHING THE DC COUPLED DRIVER TRANSISTORS 😉

Tony.

Thanks for the educated reply !


ps ROCK ON!
 
#53
Butcher said:
Those Emitter resistors are there to prevent VHF (RF) oscillation by lowering HFE (gain) It is common practice with RF amplifiers. It is a way of equalization. I cant name the correct terminology but I tink I know a tin or tew!!
Click to expand...
Should they be on the emitter side, I would agree and not ask.

But as they are on the collector side, appart from adding some miller effect , I don't get it...
 
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