Does anyone know what type of transistor should be used for Threshold
400A? Also looking for a recommended upgraded type of
transistor(250w). I have a semi-conductor test set to match but dont
want to buy a hundred TO-3's to get closely matched sets.
I think it may use a MJ15012 output @200w ea
What would be a good 250w transistor in lieu of the 200w for this amp?

John wrote:

Does anyone know what type of transistor should be used for Threshold
400A? Also looking for a recommended upgraded type of
transistor(250w). I have a semi-conductor test set to match but dont
want to buy a hundred TO-3's to get closely matched sets.
I think it may use a MJ15012 output @200w ea

What's printed on the can ?


What would be a good 250w transistor in lieu of the 200w for this amp?

I'm curious why you think you need to replace them but the MJs are now
made by On Semi. They now have MJ21193/4 that are higher power
complementary pair with the latest diffusion technology. Might not be
stable in an old design though, due to higher ft.

http://www.onsemi.com/pub/Collateral/MJ21193-D.PDF

If your output stage is simply NPN only ( quasi-complementary ), I suggest
that a new amp may be in order if you value sound quality.


Graham

Do the amplifier transistors have current limiting resistors -- usually 0.2
ohms -- these will help balance the load if you are using unmatched devices.

I have a few hundred of the 21193/94 devices in stock -- if you need matched
let me know.
http://www.tech-diy.com/hexfets.htm


"John" wrote in message
om...
Does anyone know what type of transistor should be used for Threshold
400A? Also looking for a recommended upgraded type of
transistor(250w). I have a semi-conductor test set to match but dont
want to buy a hundred TO-3's to get closely matched sets.
I think it may use a MJ15012 output @200w ea
What would be a good 250w transistor in lieu of the 200w for this amp?