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K 250 Bass Head [message #23225] Thu, 02 July 2015 16:46 Go to next message
oren hudson is currently offline  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.
Re: K 250 Bass Head [message #23226 is a reply to message #23225] Thu, 02 July 2015 17:58 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
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.
Re: K 250 Bass Head [message #23230 is a reply to message #23226] Thu, 02 July 2015 22:27 Go to previous messageGo to next message
oren hudson is currently offline  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.
Re: K 250 Bass Head [message #23234 is a reply to message #23230] Fri, 03 July 2015 02:57 Go to previous messageGo to next message
Iowa Boy is currently offline  Iowa Boy
Messages: 767
Registered: June 2014
Senior Member
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.
Re: K 250 Bass Head [message #23236 is a reply to message #23225] Fri, 03 July 2015 06:28 Go to previous messageGo to next message
stevem is currently offline  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!
Re: K 250 Bass Head [message #23372 is a reply to message #23236] Sat, 11 July 2015 13:03 Go to previous message
oren hudson is currently offline  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.
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