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Old 15th July 2002, 01:15 AM   #1
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Default Pops and Hisses from garage sale...

I purchanced a Bell Sound Systems Tube Amp from a garage sale for $30 bucks and all the tubes lit up. I pluged it into a speaker and a cd player and it produces music fine... sounds great!! Although during the silent moments the pops and hisses are very apparent. I bought it so i can learn about tube amps and maybe i'll get a chance to clean one up and fix it. Looks like i got what i was looking for. Does anyone have any suggestions where i should start to trouble shoot, or any books that would help.

Thanks,

Virgil
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Old 15th July 2002, 02:59 AM   #2
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Hi, when you get pops and hisses in a tube amp it can be a number of things. Most likely are bad high voltage connections such as dirty pins on a tube socket or a loose solder joint. Other less likely causes are a gassy tube or a microphonic tube or a dirty potentiometer for adjustment of some sort. You first try should be to try and clean the tube sockets as well as you can but carefully and don't use a cleaner that has too much oil in it. Preferably tv tuner cleaner or something like that. If you can fit a pipe cleaner into the pinholes this is good, but not too likely for miniature tube sockets which have very small holes. Most poppy hissy amp I had just had dirty connections and a good thorough clean out always fixed the problem for me.

Good luck with your amp, you're lucky to even get a garage sale amp that works at all!
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Old 15th July 2002, 10:30 AM   #3
SHiFTY is offline SHiFTY  New Zealand
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What a bargain!!!!

If its a really loud BANG it could be your B+ filter capacitors, the hi voltage can types. If you suspect this, then just change em, in fact its a good idea to replace all old capacitors with modern types, they tend to get leaky and fry things. However if its just some hiss and clicking sounds, its likely to be your preamp tubes have slightly corroded legs and there is some resistance... Easy fix (ie clean them!). Just watch out when you clean the glass of the tubes, the paint comes off real easy, and its a shame to lose those cool logos.

Welcome to the world of tubes! You can get great sound out of a tube amp, I was blown away by mine. For info, I go to google.com groups and search for whatever. You might be able to find a schematic somewhere online... Good luck!
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Old 15th July 2002, 11:07 AM   #4
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Discharge the caps then resolder every joint.

If that doesnt help replace all the pots, zeners and electrolytic caps as these are the most common sources of noise and it is possible the tubes are also reaching the end of their life.

Although unlikely it is also possible that poor grounding of the heater elements is causing hum; however, i would say this is unlikely given that this is a commercial product.

Given the original price you paid even if you have to do all of the above, you will still have spent a comparatively small amount of money while you will also gain invaluable experience.
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Old 15th July 2002, 11:18 AM   #5
Duo is offline Duo  Canada
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audiofreak: What about dirty sockets? These are more likely to cause popping and hissing in a tube amp. Do you know how much a bad connection can ark at those voltages?

EDIT: Hum wasn't the problem, it was microphonics or general arking sounds at low volumes.
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Old 15th July 2002, 01:59 PM   #6
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Yep Duo thanks for keeping me inline with that one ... indeed the sockets sound as though they are a likely suspect. I'd probably replace those while resoldering all the joints. And yes Duo I've seen first hand how much a bad connection can ark even at voltages much much lower than this.
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Old 15th July 2002, 02:41 PM   #7
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Okay, sorry if I offended you but that just seemed to be the common case in my experience with tubes more than caps and solder. Of course, if I think it's worth it I always replace all the solder and caps too cause it does make a huge difference in sound quality.
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Old 15th July 2002, 03:17 PM   #8
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Thank you all for the help!! i'll be sure to do things in this order:

1. Clean everything first... (would alcohol be okay to use or does it really have to be that tv tuner stuff?)
2. Discharge all the caps and replace all the solders... I remember discharging caps in my electricity and electornics class but all i remember is him telling us not to stick our tounges on the caps. then he put the cap under a piece of paper and used a screw driver to connect the + -. It blew a hole through the paper... So could someone refresh my memory on how to properly do this... Thanks...
3. Change all the pots and sockets.

Thanks again for all your help!!
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Old 15th July 2002, 03:36 PM   #9
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Default Discharging caps.

I would put a fairly highvalue power resistor
across the + - points.
You could solder 2 plasted copper wires
to power resistor.

Initial current
300 volts/ 10 kohm= 0.03A at start
Initial effect
300x0.03= 9W for a short period
That would a 2-5W resistor withstand

gromanswe
afraid of sparkles
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Old 15th July 2002, 03:57 PM   #10
Duo is offline Duo  Canada
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Yes alchohol works just fine, just try not to be sloppy.
A good tool to have is a small toothbrush or something with hard bristles to clean contacts and things. About discharging a cap, using a power resistor is the proper method to do this. Another way is to simply short the cap to ground but you get some pretty big sparks and arc welds this way with big caps. I once tried shorting out a 500000uF cap with a screwdriver and I had great trouble trying to pry it back off of the capacitor pins! It's also hard on hearing too. Generally, a 10k or 5k power resistor is good for cap discharging, it's nice to solder some test leads or clips to the resistor so you can easily make contact with the cap. Once you have let the resistor sit on the cap for a while you should then short it right out to make sure there is no more charge in the cap.
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