oren hudson Messages: 274 Registered: March 2008 Location: Gastonia, NC
Senior Member
So I'm rehabbing this '71 250 head. Cleaned and Deoxed the inside. Turned it on and everything worked fine - except the blue power and polarity bulbs did not light up. I replaced the bulbs, but still no light. Both switches work fine, just no blue lights. Any ideas? Thanks.
The two bulbs are powered from different sides of the power supply, so for both to be out is odd. Maybe the bulbs are not screwed in tight enough?
If you look at the back of the push switches, you should be able to see the two terminals that connect to the light sockets. They are not part of the big switch block.
Trace the wires, one should be grounded to the front panel and the other goes to a large black resistor that is mounted to the chassis. Make sure the wires are all connected and if you have a meter, test the resistance of the big resistors. They should be somewhere around 400 ohms. Of course do this with the amp unplugged.
oren hudson Messages: 274 Registered: March 2008 Location: Gastonia, NC
Senior Member
Thanks cb. I really appreciate the info. I hope to get some more time for it over the July 4th holiday. Those switches aren't available any longer are they? Thanks again.
Stevem did find replacement switches but think he had posted that they run around $65 each. Definitely sounds like you have a ground issue with the bulbs if they aren't screwed in tight.
stevem Messages: 4728 Registered: June 2004 Location: NY
Senior Member
Yes, I have stock of switches now that will work, but his issue does not sound like the switch, as Bill posted about .
At the time I was scowering the planet for these new switches I was also looking for a white LED to replace those GE 335 bulbs, but I never finished my search on that!
oren hudson Messages: 274 Registered: March 2008 Location: Gastonia, NC
Senior Member
After checking the wiring as set out by chicagobill and finding everything in order, I ordered some new bulbs from Mouser. I've just had the chance to try them. Blue lights abound! Must have been "bad" new bulbs that I had put in. Now everything is far out. Thanks for everyone's input.