SVT CL Trips At High Power

[Ted]

Billy - I thought 22R seemed a little low. Any suggestions for a higher value?

[Prairie Dawg]

There's an Ampeg service bulletin that ups the screen resistance value to 220 ohms, Ampeg recommends 1/2 w flameproof resistors.

[Ted]

I notice that the 22R resistors have diodes in parallel with them. Which allow the screen grid current to increase once the voltage across the 22Rs exceeds their threshold voltage. I'm guessing that they should probably go if I'm fitting 220R.

[Ted]

I removed the diodes. The 220R resistors worked a treat.

Moral of this story: New Production Svetlana Winged Cs are not the same as Old Production...

[Ted]

These are the mods I mentioned.


SVT CL Pre Bd Fault.pdfSVT CL Pwr Bd Fault.pdf

[Jazz P Bass]

Uhmm.
The pdf files are blank.
Can you try to repost them?
When you do, test your post by trying to open the file.

[Prairie Dawg]

That's what the service bulletin said to do. If you are going to work on SVTs you need a good way to evaluate tubes and the only way to do this is to build it yourself. I've run 6550s at 600v on my tube matcher but I did get a little nervous-that's a lotta juice.