Greetings! Why is there sometimes a capacitor and resistor between the 2 plates of amplifiuers Ex.6L6 ,not going to ground ,just from plate to plate in push pull configuration?Thanks for any information!

:Greetings! Why is there sometimes a capacitor and resistor between the 2 plates of amplifiuers Ex.6L6 ,not going to ground ,just from plate to plate in push pull configuration?Thanks for any information!

Hi Chris,
In single ended outputs you always see a capacitor across the input of the output transformer. This capacitor tunes the frequency response of the output transformer form for optimum tone quality.
The plate to plate capacitor in a push pull amplifier is also across the output transformer, tuning its frequency response.
If a tone control is included in a set, it is a variable resistor in series with another capacitor all across the primary of the output transformer, modifying the tone further.

These capacitors typically have to deal with high surge currents. If they are old paper wax capacitors they are always bad, and among the first on the list for replacement.

Bst Regards,

Bill Grimm