| K25-2 [message #18295] |
Thu, 28 February 2013 12:48  |
Woolsocks
Messages: 4
Registered: February 2013
Location: ct
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Junior Member |
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I just picked up a 1970 k25 Mostly working but needs a little help amp. I was wondering if anybody had a schematic and/or parts list. And if you have any helpful sites to check out this is my first solid state amp and first Kustom.
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| Re: K25-2 [message #18296 is a reply to message #18295] |
Thu, 28 February 2013 14:55  |
Kustom_Bart
Messages: 601
Registered: October 2010
Location: Greenville, MichiGUN
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Senior Member |
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Very nice grab! The K25 and K50 are the best sounding little amps that you will find. you can gig with them with a processor pedal in front of them and keep up with about anything. They are a great lil amp and only weigh 46lbs too. Let me look and see if I have any schematics for a K25. I know I have them for a K50 and Challenger, but not sure about the K25. I will look. Shoot me a PM with your e-mail address I did find them, I will e-mail them to you.
What kind of problems are you having with it?
[Updated on: Thu, 28 February 2013 15:14] Report message to a moderator |
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| Re: K25-2 [message #18504 is a reply to message #18295] |
Mon, 25 March 2013 12:44 |
chicagobill
Messages: 2005
Registered: April 2003
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Senior Member |
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Your description of "short, fuzzy and no sustain" sounds like it could be a power amp problem.
What sort of skill set do you have and what sort of test equipment do you have access to?
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| Re: K25-2 [message #18508 is a reply to message #18295] |
Mon, 25 March 2013 18:18 |
stevem
Messages: 4748
Registered: June 2004
Location: NY
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Senior Member |
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The first thing you can do is leave the amp on for 5 to 6 hours, as this may help the caps reform themselves if the are not too far gone.
In these amps the only sourse of a electric shock that can harm/kill you is the a/c volatge into the PT and out to the rectifier bridge and then that gets split in to two 40 volt rails that feed off of each main filter can.
This voltage at the cans is a good first place to check out things with the power supply.
If you place your voltmeter across the sprapped center connection points on the cans, and then to each out side can terminal you should read a + 38 to 41 volts DC, and the other way a _ DC voltage in the same range.
Also I see you are in CT, would that be in the eastern side of the state, like the Danbury rt84 end by any chance?
[Updated on: Mon, 25 March 2013 18:19] Report message to a moderator |
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| Re: K25-2 [message #18527 is a reply to message #18295] |
Tue, 26 March 2013 17:09 |
chicagobill
Messages: 2005
Registered: April 2003
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Senior Member |
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When electrolytic capacitors age, they essentially start to dry out. These types of caps can have their electrolyte reformed by heat or by an application of voltage in a series of timed applications. Reforming the electrolyte can make an old cap work like new.
That being said, if the amp has been turned on regularly during its lifetime, there probably is no need to try and reform the caps.
I'd suggest that you start as Steve said by testing power supply voltages. Kustom schematics are covered with typical voltages marked at different points in the circuit. Compare the voltage readings that you get in your amp with those listed on the schematic. I would pay particular attention to the bias voltages on the output transistors.
If you haven't worked on an amp with a live chassis before, please be certain to take all of the safety precautions available to you before you start. Never try and do more than you are capable of. If you have a friend with more experience, see if they can help you. Just be aware at all times that there are voltages in there that can hurt or kill you.
And remember that a slip of your meter probe can cause a short circuit that can do major damage to the amp. So work slowly and carefully. And be sure to unplug the amp as soon as you have finished taking the voltage readings. Don't just turn off the switch, pull the plug.
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