Do you have the transistor’s part number? A photo of the device will be nice.
I don’t want to discourage you, but TO-3 packaged transistors will give you a sticker shock.

Money is no object.

I am unsure of the part numbers as of yet. Hopefully, they will reveal themselves as i continue the disassembly.

I suspect the OEM parts will be long discontinued. I hope the audio experts here will help me zero in on suitable replacements.

 

2N3055 (NPN) and MJ2955 (PNP) is a common complementary pair.

 

Joey not sure what part he has.
C'mon !! Take the freakin' thing apart. Show me some guts

 

The table shows all are dead. !!

Darn ! You are the first to blow the complete power stage. AFAIK.

 

2N3055 (NPN) and MJ2955 (PNP) is a common complementary pair.

300W into 4Ω would require ±50V supplies assuming no loss, no output resistors and no ripple so a 60V transistor isn’t going to work.
Vceo rating have to be quite high to avoid the secondary breakdown part of the safe operating area curve.

 

Joey not sure what part he has.
C'mon !! Take the freakin' thing apart. Show me some guts

The last time I handled a discrete transistor linear amplifier was in an EEN204 lab at university over 100 years ago.

The last time I dealt with a 600W discrete transistor power amp was......never.

I like this amp...it's got history (it's the one and only thing I ever stole from a church). I'd like it to work again, someday.

That, and I don't have a lot of time to spend on it.

I am good at what I'm good at, and this ain't one of them.

300W into 4Ω would require ±50V supplies assuming no loss, no output resistors and no ripple so a 60V transistor isn’t going to work.
Vceo rating have to be quite high to avoid the secondary breakdown part of the safe operating area curve.

This is why I'm here. Thanks, for your continued help, Ian.

BTW, I suspect -- from posts I've read on the internet -- these parts will be suitable:

https://www.onsemi.com/download/data-sheet/pdf/mj15022-d.pdf
https://www.onsemi.com/download/data-sheet/pdf/mj15023-d.pdf

Comments?

 

For my next project, I've got 2 non-functional Tektronics 2465 analog oscilloscopes, and a 2445.

Who wants to help turning 3 dead scopes into one live one?

 

This is why I'm here. Thanks, for your continued help, Ian.

BTW, I suspect -- from posts I've read on the internet -- these parts will be suitable:

https://www.onsemi.com/download/data-sheet/pdf/mj15022-d.pdf
https://www.onsemi.com/download/data-sheet/pdf/mj15023-d.pdf

Comments?

I was going to send you to On-Semi’s website.
MJ15022/23 would work well. Note that the secondary breakdown doesn’t start until there is 60V across the device, so isn’t a problem.
MJ15003/4 are Also common for this type of amplifier.

 

For my next project, I've got 2 non-functional Tektronics 2465 analog oscilloscopes, and a 2445.

Who wants to help turning 3 dead scopes into one live one?

I believe Chips will be good doing scopes.

As for the amp, you won't mess it up.
We got you

 

BTW, I suspect -- from posts I've read on the internet -- these parts will be suitable:

https://www.onsemi.com/download/data-sheet/pdf/mj15022-d.pdf
https://www.onsemi.com/download/data-sheet/pdf/mj15023-d.pdf

Comments?

Good choices. They have a large SOA. Should be able to withstand abuse.

Either pair should be work, the first pair is 200 VCEmax, the other 250VCEmax.

 

 

View attachment 344469

View attachment 344470

 

Right?

 

View attachment 344472

Right?

Bingo!

 

House numbers, meaning that they are a commercial parts which have been screened for a particular parameter, most likely Hfe.
I am sure that I already know this answer, but I will ask the question; can you test for Hfe?

EDIT;
The same PDF file has the note that house numbers are selected for gain

 

House numbers, meaning that they are a commercial parts which have been screened for a particular parameter, most likely Hfe.
I am sure that I already know this answer, but I will ask the question; can you test for Hfe?

EDIT;
The same PDF file has the note that house numbers are selected for gain

That was going to be my next question: do I just buy 6 of each PNP and NPN, or do I need to buy extras and match for some parameter(s) like hfe and Vbe?

Or do I need to select for a minimum hfe? And, under what operating conditions?

Damn...analog is pretty annoying compared to digital.

 

That was going to be my next question: do I just buy 6 of each PNP and NPN, or do I need to buy extras and match for some parameter(s) like hfe and Vbe?

Or do I need to select for a minimum hfe? And, under what operating conditions?

Damn...analog is pretty annoying compared to digital.

Just buy 6 off each. If they are from a reputable supplier, you will get 6 out of the same batch.
The design has emitter resistors which will keep the current evenly shared.

 

Just buy 6 off each. If they are from a reputable supplier, you will get 6 out of the same batch.
The design has emitter resistors which will keep the current evenly shared.

And what about fuses: they appear to be 10A ceramic. Fast blow, slow blow?

View attachment 344326

 

And what about fuses: they appear to be 10A ceramic. Fast blow, slow blow?

View attachment 344326

Are they labelled F10A or T10A?
If they are before the main power supply capacitors then they will almost certainly be Time delay. If they are just in the output stage they should be Fast.

 

Are they labelled F10A or T10A?
If they are before the main power supply capacitors then they will almost certainly be Time delay. If they are just in the output stage they should be Fast.

Sticker on the board says F10A.