Ampeg V4 Standby Light

[dusty]

I've got an early 70's V4. I just installed a bunch of parts from fliptops.com. I put in new power and standby switches, and power and standby lights.

The power light was fine before I changed it out, the standby light didn't work and I assumed the lamp was bad. I bought the set and swapped them both out. Power light works fine but standby light still doesn't work.

Any help on where I might start looking for the problem? Anyone else had this happen? I haven't tested either light yet, which i should probably do first. Should I just hook up some voltage (like 5V) to it and see if it glows? Or do these run off of mains current?

That's a lot of questions...

[Tom Phillips]

V-4 Uses Neon Pilot Lights

Dusty,
The V4 uses neon pilot lights. They run on fairly high voltage so will not light at all with 5V across them even if good. The standby light (actually I'd call it an "Operate" light because it in on when the amp is in operate mode) is fed from the amps high voltage B+ supply through a series resistor. I believe that the resistor is 180k Ohms and is designated R221. If that resistor is bad or the connection is bad then the light will not work. I'd check there first since both old and new lights do not work.
Good luck,
Tom

[dusty]

thanks

thanks Tom.

The whole standby/operate light always struck me as odd. I would prefer it to be on in standby, as in "standby mode is enabled" and not the other way around. I'll crack it open and have a look at that resistor because I know the connection to the board is A-OK.

[methodofcontrol]

yeah...that 180k is a typical failure for the standby light. every V-series ampeg i've ever worked on w/ a blown standby light......that one resistor is always the problem.

[Enzo]

To me the standby light is intuitive. The mains power light comes on with the mains power, and the B+ light comes on when the standby switch enables the B+.

You wouldn't wire the switches so that up was on for mains but up was in standby for that switch, would you? Indicator lights most of the time light up for circuit active. I could see the light changing color to mean standby or operate, but coming on to indicate non-operating status rubs me wrong.

[dusty]

R221 was NG

Yep. That did it. Looking at the schem after Tom's first post, it was staring me right in the face.

Enzo, I understand your point of view about the standby light. Better to show that B+ is on, in hindsight.

Thanks for your help. This forum is great.