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Old 4th June 2012, 09:14 PM   #1
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Default power section pops like frying bacon

I am attempting to repair a guitar amp that belongs to a friend of mine. I isolated the power section and power supply from the preamp and tone controls. Its making random pops and crackles as if I am wiggling a loose connection. The power supply is a simple unregulated bridge rectifier and 2 caps. The amp is a TIP35 and 36.

I have re-soldered all of the component connections and changed all of the electrolytic caps with no success. What you recommend next?
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Old 4th June 2012, 09:41 PM   #2
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Hi Pbassred,

this could be a cold solder joint.
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Old 5th June 2012, 12:21 AM   #3
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.....Or a deep-fried semi, assuming you have no sound. Did you have some output before dismantling?. If not, run a DVM over the base emitter junctions and verify there is ~0.6V across each. junction.
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Old 5th June 2012, 02:45 AM   #4
wg_ski is offline wg_ski  United States
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Highest on my suspect list would be the input transistor(s) of the power section. That is, the one that follows the tone/volume control section. That's where noise from a bad transistor or cold solder joint would bother it the most and be noticeable.
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Old 5th June 2012, 06:26 AM   #5
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It works properly as an amplifier. I had already reflowed the solder joints so it can't be a cold joint. I'll swap the input transistors and see where that gets us.
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Old 5th June 2012, 11:41 AM   #6
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Although the other causes are more likely I am sure, I had a frying bacon noise (low) on both channels in a power amp from some tantalum input caps (5.0 uf) I installed. Caps were purchased at RK distributing, a local parts store. Had it from the day I activated the purchased dead amp until 20 years later when I replace the caps again. Wasn't any internet in those days, didn't know what to expect from a transistor amp. This replacement time I used 4.7 uf 50V CPO ceramic caps. Much better! Still have the OEM (original equipment manufacturer's) 1970 transistors on one channel.
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Old 5th June 2012, 01:29 PM   #7
sbrads is offline sbrads  United Kingdom
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Freezer spray is good for helping to find such faults. Apart from joints and caps, don't forget resistors. I've seen lots of usually high value (>47k) resistors go dodgy after several years if the leads are bent close to the body.
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Old 5th June 2012, 01:43 PM   #8
DF96 is offline DF96  England
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Reflowing joints can make them worse, while at the same time hiding the evidence by giving them all a nice shiny appearance. Bad joints should be redone, the rest left untouched.
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Old 5th June 2012, 04:17 PM   #9
jitter is offline jitter  Netherlands
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Quote:
Originally Posted by wg_ski View Post
Highest on my suspect list would be the input transistor(s) of the power section. That is, the one that follows the tone/volume control section. That's where noise from a bad transistor or cold solder joint would bother it the most and be noticeable.
Perhaps this amp suffers from popcorn noise. If that is indeed the case, I would suspect a high gain circuit.
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Old 5th June 2012, 05:09 PM   #10
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I think that popcorn noise is intrinsic to the device. i.e it would have sounded that way from the time of manufacture.
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