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K250-4 Selective Boost Issue [message #23124]

Mon, 15 June 2015 10:08

fullblare
Messages: 5
Registered: October 2012
Location: Sioux City

Junior Member

I've been restoring a K250-4 Amp that I purchased locally. Thanks to this this forum I have been able to build a food switch to turn on and off the Fuzz, Selective Boost, Reverb and Tremelo. The only issue I'm having is the selective boost works only for a few seconds when you first turn on the amp and then quits. I have the pedal that came with the amp and have tested it to make sure the potentiometer is good and the cord appears to be good as well. With my electronics knowledge it almost sounds like a bad cap in the RC circuit. Looking at the schematic and "S2" Selective boost cirecuit I'm wondering which cap I should be looking at. Has anyone else run into this issue?

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Re: K250-4 Selective Boost Issue [message #23125 is a reply to message #23124]

Mon, 15 June 2015 15:29

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

I'm not sure I understand what you are saying. You are using a boost pedal (wah wah) with the amp and the effect stops working after a few seconds? Is this correct?

Does the effect work okay without the wah pedal?

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Re: K250-4 Selective Boost Issue [message #23126 is a reply to message #23124]

Tue, 16 June 2015 06:01

stevem
Messages: 4773
Registered: June 2004
Location: NY

Senior Member

I am not sure what you mean also , do mean the selectone feature that one of the channels has?

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Re: K250-4 Selective Boost Issue [message #23129 is a reply to message #23124]

Wed, 17 June 2015 11:29

stevem
Messages: 4773
Registered: June 2004
Location: NY

Senior Member

So the Boost only works for a few seconds no matter which notch you have it set for?

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Re: K250-4 Selective Boost Issue [message #23134 is a reply to message #23124]

Thu, 18 June 2015 08:36

fullblare
Messages: 5
Registered: October 2012
Location: Sioux City

Junior Member

With both the boost pedal and switch board unplugged the selective boost knob on the amp seems to work in each position changing the tone of the guitar. If I plug just the boost pedal in the effect works when rocking back and forth on the pedal for a minute or so and but then has no effect.

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Re: K250-4 Selective Boost Issue [message #23450 is a reply to message #23124]

Thu, 16 July 2015 16:10

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

I'm sorry. but I hadn't noticed your new post.

If the wah pedal stops working after a short time, I would suggest that you clean the plug and jack connections and check the wah pedal pot. The wah pedal is in series with the ground connection of the boost circuit and the frequency shifts depending upon how much resistance is added in the series circuit. If the circuit works otherwise with the switch, then the pedal pot, wire and connectors would all be the first things to check.

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Re: K250-4 Selective Boost Issue [message #23453 is a reply to message #23450]

Fri, 17 July 2015 00:45

Iowa Boy
Messages: 767
Registered: June 2014

Senior Member

Cool that you have been able to build a footswitch for your amp. There are several of us on this site that are in need of a footswitch like this. Could you post on here the material you used and where you found the parts as well as a diagram of the wiring?

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