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Old 10th Dec 2008, 9:47 pm   #10
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
Default Re: Sound Sales PX4 Amplifier

Peter is right, the audio coupling caps are drawn to the wrong 6SN7GT anodes. The 6SN7GT is a phase splitter and takes a proportion of the output from the first half to feed the 2nd half via the pot that allows the gain to be balanced. Hence my earlier comment that the correct way to balance the amplifier is to put a scope across the 470ohms cathode bias, inject a sine wave and trim the pot to show the minimum AC amplitude which will occur when the PX4 are delivering the exact same output.

There is no method for DC bias adjustment so you just have to put up with the difference in anode current which will cause it to enter class B at a lower output than it should. (or redesign the output to use seperate cathode bias with bypass caps)
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