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Circuit issues with Sunn Concert Bass

J

Jeffbo

Jul 14, 2011
21
0
#1
So I bought this '73 sunn concert bass off ebay for super cheap, the "as is" in the description shouldve been a red flag but I decided to gamble. I played it for the first time today and it sounds like dookum. Super crackly when I turned the volume knob. Really fuzzed out on pretty much every aspect (not in a good way). So I popped the top and used some contact cleaner in and around everything and twisted the knobs to get the dust out when I noticed this:

33c74c4d.jpg


Looks like wads of gum and one of the wires above it is worn down. It looks as though someone tried to fix something at some point? I dunno, but I think its time to take it in to a professional, unless you guys have any ideas?

TL;DL MY AMP HAS GUM IN ITS CIRCUITS
 
#2
That looks like red RTV silicon glue, likely used to keep the caps from vibrating and breaking off the circuit board. Could be original but I'm not sure, it's been years since I worked on the Concert bass head I had.

The yellow cap might not be original--but the two silver caps are original. This amp at the minimum needs a cap job. All electrolytics should be replaced--would you try to drive a car (with your family in it) on the freeway with 40 year old tires on it?

There could be an output transistor fried, hence the fuzz, or the tired old caps may be contributing to the fuzz, or it could be a poor connection. Notice all the wires that push on with those chintzy little connectors everywhere. And check the main power amp board, is it flopping around because the plastic standoffs have broken?

Sadly, a tech would likely charge more than the amp is worth. Where are you located? I could at least look at it for you and offer more advise if you were in the Nashville area.

edit: p.s., I think this amp is from late '74, the date code on the cap seems to be the 31st week of '74 and the date code on the pot is also '74. So the amp can't be newer than the stuff the factory put in it.
 
#3
So what you're saying is, this amp will kill my family if i drive it on the freeway? But as far a solidarity goes, it's great. Nothing is rattling around or seems out of place. The only thing missing is a ground on the wall plug but I can replace that easily. Sadly im located in the pacific northwest. Portland Oregon to be specific. Amp repair shops are a dime a dozen here so maybe I'll luck out with a guy who won't break my kneecaps for a repair. I really do appreciate the insight, though
 

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