Fisher x100A's Phase inverter.

[iswind]

What is phase inverter? How to adjust the hum from it?

 

[battradio]

Don't have the schematic in front of me but , it is not a hum ajustment . It is used to minimise distortion. You need a signal generator and scope or a distortion analyzer to adjust it . Replace the filter and coupling caps and most likely the hum will go away .

 

[kvflyer]

When you have a push-pull output, your output tubes conduct out of phase with each other. So, what you must do is to have a tube from which you can send the signal from the plate to one output tube grid during the positive part of the signal and then from the cathode during the negative part of the cycle. Then, both output tubes work one after the other to amplify the signal completely. Often, you have a tube like a 6U8 that uses the pentode section as a voltage amplifier and the triode is used for the phase inverter. Look at the schematic of an HH Scott amplifier, like the LK-72B and you can see the signal being picked off of the triode section...

 

[Al Taylor]

This is a great site that has a rundown of several different types of phase inverters.
http://www.freewebs.com/valvewizard/index.html

 

[Patrice B]

Alternate method (Audacity and DVM) http://www.audiokarma.org/forums/showthread.php?t=287520&highlight=AC+balance

Posts 6 and 7 particularly

Patrice

 

[iswind]

Thank you, every one.
Regards