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Kustom 200 A-4 (Earlier) [message #24291]

Thu, 31 December 2015 19:56

Shaun_Musings
Messages: 323
Registered: April 2009
Location: Reading, MA

Senior Member

So I have 2 A-4 heads (lucky me!) One is strong (hiss from Trem/Vib channel, fuzz works odd, but other than that, no complaints). The other one is weaker, the Selectone doesn't work, and while the trem/vib is strong, and the clipper is strong, there is no reverb.

I have decided to start working on this A-4, which has a lower serial number and a limited number of those Orange Drops that the other one does. I was playing on it, and it sounded okay, but then all of a sudden it started popping and the wouldn't let a guitar signal pass.

After talking with Don, Terry, and Brian (Great guys!!! =) I started replacing the Mallory caps on both the volume boards and the boards on the back wall (I did not replace the big 80/50v ones... Somehow I just didn't see them). I made sure they went in the right place and positions, and fired it up. The popping noise was not nearly as loud, but there was still no guitar signal.

Replaced the NTE transistors (The ones that look like 'D'). Now what's interesting is that one of the round head caps had been sliced off and soldered back on. Which made me wonder three things:
1. This amp has been worked on before; are there any other transistors in wrong,
2. Are there any wiring connections that are actually bad and need to be replaced?
3. Why is there so much flux residue and rust in here? My other A-4 is clean as a whistle!

Started cleaning. I cleaned the output jack and put it back in, cleaned the input jack and put them back in. Started it up. Before, there was about ten seconds before the popping started. Now it starts immediately.

Tested the big filter caps there in the middle, the Coke cans. The one on the right closest to the OT is reading 40V, but the other one fluctuates so fast I can't even get a value. Not sure what this means, not sure if it's normal (the amp was plugged in and turned on but the speaker was unplugged).

So, what I have ordered from Mouser are the bottom transistors: MJ15015G, which someone here said is a 'beefier' version (I swear, I stalk on this site all the time) and the 2N5008 to replace the little round three-legged transistors.

Is there anything I have missed? How do I tell which 'leg' goes in which hole on the board? If things have been moved around, I want to make sure I put them the right way.

SDC

Born on the Baaaaayou (Ok, in Massachusetts)

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