- Feb 3, 2020
- South East Asia (not China or SAR's)
Not sure about "first", but definitely
Thank you. TF80/60 had a Beta of approx. 50 in this circuit, think thats enough for good filtering of the push pull output stage of this 10W power amp.
PP Outputstages have quite high PSRR. At least while operating in Class A.
Is there something better available today with bipolar transistors?
MJE350 would drop in and is available.
This isn't a high voltage type, but it's employed in a high voltage PSU. Has this been achieved because it's placed in the negative part of the PSU?
No. I suspect that when circuit starts up the 5k/50u = 250milliSec causes a quick voltage rise. Plus other than charging the capacitors via large value resistors there is no current flow (heaters are still cold).
So with nowhere for current to flow, even if the transistor goes into "avalanche", without current flow this is largely inconsequential and by the time tubes conduct the transistor will be back in normal operation.
It is a way that nowadays is generally avoided, as suitable alternative parts exist that do not need to be operated under conditions exceeding limits.
I could imagine when someone is "pumping" a breaker with this circuit attached the transistor may very well pop.
Can someone use a modern type of PNP low voltage transistor and replicate this PSU for a tube amp easily?
Probably yes, with all the caveats applying to the original version. It is considered poor design practice.
Does this type of transistor in general eliminate the need for a high voltage bipolar transistor in tube amp PSU? It would have been a clever idea.
No, because it still operates under conditions that have the potential to be destructive, just not under normal careful operation.