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Old 10th June 2009, 11:06 AM   #1
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Default Old amp kit making noise and its getting OLD.

Here is a curious diagnostic problem:

I have this old s-5 electronics push-pull tube amp kit that I am pretty much done with as far as sound quality, but now I want it to be the main piece in a second system. I fired it up the other day and it has this habit of the right channel starting to kind of crackle crackle and sometimes it makes a tube rush sound. If I whack the top of the case (yes, I employed such primitive methods) then it makes a final big "Crack!" and then the right channel is back to normal until the cycle repeats about 5 minutes or less later. I think that it may be either a bad tube in the right channel, bad PCB isolation from outside vibration, or a wiring issue? I am no tube expert so if anyone has any ideas I would greatly appreciate them!

Thanks,
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Old 10th June 2009, 12:29 PM   #2
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COuld be dirty posts on the tubes, or a tube going bad. Try swapping the tubes from the right and left channels. If the problem moves then it's the tubes.
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Old 10th June 2009, 12:33 PM   #3
chrish is offline chrish  Australia
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Or might be a cold solder joint that starts playing up when things get warm. Try the sockets and tubes suggested above first, no point opening up if you don't have to.

Chris
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Old 10th June 2009, 10:02 PM   #4
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How do you know if a solder joint is a cold?
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Old 11th June 2009, 03:16 AM   #5
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Quote:
Originally posted by ambience exists
How do you know if a solder joint is a cold?
Take it's temperature! Sorry, I couldn't resist...

Sometimes you can see them. Get a magnifying glass and and look for cracks or dull solder. Good joints should be shiny and very smooth. Reheat/reflow any bad joints with a solder iron.

The other trick I use is to take a small wooden dowel or bamboo chopstick and use it to tap or push the solder connections while the unit is on. If your tapping or pushing causes any change in sound you have found the culprit. Just be VERY careful doing this as there are LETHAL VOLTAGES present.

Bill
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Old 11th June 2009, 08:25 AM   #6
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Default Re: Old amp kit making noise and its getting OLD.

Quote:
Originally posted by ambience exists
Here is a curious diagnostic problem:

--> about 5 minutes or less later. I think that it may be either a bad tube in the right channel, bad PCB isolation from outside vibration, or a wiring issue? I am no tube expert so if anyone has any ideas I would greatly appreciate them!

Thanks,
((AE))

Possibilities;
valve sockets, these rank high on dodgy contacts;
Older type capacitors have poor internals
A tube at end of life.
Check B+ connections; (becareful with this- use insulated tool)
Solder joints on pcb where power resistors are used; on old TV's this used to be the No1 fault.

richy
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Old 11th June 2009, 10:46 AM   #7
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Thanks.

I wont be able to check these things for a while as I am living in another state for a while for my job but thanks for the advice!

Peace!
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