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K 250 Bass Head [message #23225]

Thu, 02 July 2015 16:46

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.

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Re: K 250 Bass Head [message #23226 is a reply to message #23225]

Thu, 02 July 2015 17:58

chicagobill
Messages: 2006
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.

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Re: K 250 Bass Head [message #23230 is a reply to message #23226]

Thu, 02 July 2015 22:27

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.

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Re: K 250 Bass Head [message #23234 is a reply to message #23230]

Fri, 03 July 2015 02:57

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.

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Re: K 250 Bass Head [message #23236 is a reply to message #23225]

Fri, 03 July 2015 06:28

stevem
Messages: 4775
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!

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Re: K 250 Bass Head [message #23372 is a reply to message #23236]

Sat, 11 July 2015 13:03

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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