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This is a late 80's Ampeg SVT-II. I found that of the 6 power tubes only 1 was working at full strength. :( With new 6550s installed at idle it seemed fine but when driven some tubes would exceed 200mA while others were only drawing around 80mA. This amp had a bias problem and was destroying power tubes. Coupling caps in the phase inverter were responsible for the uneven drive. SVT at idle is displayed on the meters -- 670Va at 23.6mA per tube.

This is a late 80’s Ampeg SVT-II. I found that of the 6 power tubes only 1 was working at full strength :(
With new 6550s installed at idle it seemed fine but when driven some tubes would exceed 200mA while others were only drawing around 80mA.
This amp had a bias problem and was destroying power tubes. Coupling caps in the phase inverter were responsible for the uneven drive.
SVT at idle is displayed on the meters — 670Va at 23.6mA per tube.  The picture above which is the header of the page shows SVT with signal applied.

Massive SVT has a preamp board on the right and power amp and power supply on the left PCB. This amp has been worked on a few times before as you can see the red wire which is hardwiring a burnt out trace.

Massive SVT has a preamp board on the right and power amp and power supply on the left PCB. This amp has been worked on a few times before as you can see the red wire which is hardwiring a burnt out trace.

IMG_0912

After repair doing 33.7V into 4 ohms for 284W at the onset of clipping.

After repair doing 33.7V into 4 ohms for 284W at the onset of clipping.

Ampeg SVT II block diagram

Ampeg SVT II block diagram

Ampeg SVT II preamp

Ampeg SVT II preamp

Ampeg SVT II power amp and power supply

Ampeg SVT II power amp and power supply

Ampeg SVT II graphic EQ

Ampeg SVT II graphic EQ