The push-pull output stage of this Ampeg^® SVT-VR bass amp wouldn't balance at any setting of the Balance trimpot.

The two Bias trimmers could be adjusted to light the green LEDs but when the amp was driven to an output of 25VAC at 40Hz the Balance trimmer wouldn't light the yellow LED.

In addition, the amp sounded weak when turned up.  And sometimes it would go into Standby mode by itself, or else not come out of Standby.

Since all the power tubes tested good, we decided to remove the power amp chassis and look for other problems in the output stage.

We ended up replacing four open resistors on the SVT-VR Tube Board.

These SVT-VR parts are available in our Online Store:

• 6550 Plate Resistors for the Ampeg SVT-VR:
Flameproof 5Ω, 3W, 5% Resistors

• 6550 Screen Grid Resistors for the Ampeg SVT-VR:
Flameproof 220Ω, ½W, 5% Resistors

• 6550 Cathode Resistors for the Ampeg SVT-VR:
Flameproof 1Ω, 2W, 5% Resistors

Additional Resources:

Schematics for the Ampeg SVT-VR amp

^®See trademark owners  HERE.