AMPEG SVTAV (Happy Hernia)

[DRBILL]

When it wears out it will make a splended boat anchor! It is on my bench for some simple routine issues. It has a feature that boggled my mind. There are two screwdriver pots on the back for setting the bias on the two banks of power tubes. Next to each of them are two LEDS, red and green. If you set the bias WAY too low, neither lights. When you get it too high, both light. When it is just right, the red goes out and only the green lights.

It occurred to me that this would be an excellent addition to almost every amplifier I touch. So, I rushed for the schematic to see how it was done. The rats only showed test points across 1 ohm resistors between the cathodes and ground. No suggestion of the presence of LEDS. Yeah, I know, just look the the PCs, trace it out and write it down. It would be a day's work taking it apart and another putting it back together. Nothing is easy. And I don't have a floor jack!

So, anybody out there know how this circuit works and willing to share? Wouldn't it be great to have this. You could set the bias daily, instead of once a year or never.

ANYBODY?

[artto]

Bill, I would try to contact Rick Turner http://www.renaissanceguitars.com/

Or Terry Buddingh who I believe is currently Editor, Guitar Player Magazine and previously technical writer for Bass Player Magazine. Terry specializes in restoring vintage Ampeg SVTs

[Marvel]

I think that is also the way Sound Values, later named SoundValves, built in the bias adjustment on their ST-70. I also, thought it would be a great way to bias an amp.

Bruce