Again, thanks all.
Interestingly I think 130Vrms at the plates is probably true as with the amp set in test conditions the output of the PI is heavily clipped. I put a 470k/470k divider into the PI and swapped in a 12AT7. The plates are now at 43Vrms and the amp is much more manageable. The customer wants a NFB which will help a bit more.
Interestingly I think 130Vrms at the plates is probably true as with the amp set in test conditions the output of the PI is heavily clipped. I put a 470k/470k divider into the PI and swapped in a 12AT7. The plates are now at 43Vrms and the amp is much more manageable. The customer wants a NFB which will help a bit more.
In case you didn't think of it: When using a 12AT7 instead of the 12AX7, the cathode bias resistor should be changed to 470R.
I don’t think so, and not sure where that conclusion came from. Did everything as per the spec. The thing that’s confusing is that all the components measure ok. I’m setting the signal as per the schematic and getting the right AC voltage into the LTP but not the right one out of it. Not to mention that even if I was measuring it all wrong why is the amp subjectively loud and going to 55W output with the volume pot at 1,
Must be a gremlin somewhere.
I agree that there's nothing wrong with the PI circuit.
It's actually a standard PI used in many successful amps.
But as I explained earlier the signal levels before the PI specified in the schematic are either wrong or way too large for an amp using no global NFB.
It follows that this amp should be tested with an input signal about 4 times lower than specified in the schematic.
Apart from that I'm sure that some users will like the high sensitivity/gain of this amp.
A master volume before the PI would be a good idea, though.
It's actually a standard PI used in many successful amps.
But as I explained earlier the signal levels before the PI specified in the schematic are either wrong or way too large for an amp using no global NFB.
It follows that this amp should be tested with an input signal about 4 times lower than specified in the schematic.
Apart from that I'm sure that some users will like the high sensitivity/gain of this amp.
A master volume before the PI would be a good idea, though.
