Help please, Jolida 202a hum.

gurley123 · 14th December 2009, 08:08 PM

This may be futile but i need to give it a shot.

I need some help chasing down some hum in my amp. This hum appeared about three weeks ago in my up-to-now very quiet Jolida 202a. The hum appears to be independent of volume setting or source selection. It's fairly low level but loud enough for me to hear in the quieter passages of music. I've owned this amp for about 16 years now and this is the first bit of trouble I've had with it.

Right around the time the hum showed up, I had a power tube spark on me. I think I had let the bias drift to far and that is what caused the sparking. I had heard some static right before the sparks but I thought it was in the program I was watching(my amp is not in my line of sight.) After sparking, the tube still appeared to be sealed and after biasing behaved reasonably well (it was a little erratic but I kept the multimeter handy and checked it often) but the hum was now present. Four new tubes now and the hum is still there.

I have very little knowledge of tube amps other than what I have read (lethal voltages inside!!!, it might not be that hard to change it to triode, ect.) and I know that tracking down hum problems are tricky in the first place but I thought I would ask for some help here. Maybe there's a simple fix for it (I'm not holding my breath.) I would like to thank you in advance for just coming here and reading my post and will get the wife to bake you up some awesome cookies if you can help my exorcise my noisy demon.

StephenJ · 14th December 2009, 09:15 PM

Dear gurley123,
May I ask your help.
I am new to the site and despite searching have failed to find.
How did you make your post?
Having given the details and asked the questions how did you post/get it put up on the site?
Sorry if am a burden but would be very greatful for your help.
In hopeful anticipation, thanks!
StephenJ

jerrynsr · 24th January 2012, 05:29 PM

Swap the Power Tube that sparked to the other channel. See if the hum moves with the tube. I had a defective 12AX7A, one filament was really bright. I had a hum that was uneffected by volume control so I figured the hum was getting picked up from the ac filament voltage. I moved the tube and the hum went with it. Now I have some vintage NOS preamp tubes on the way.

speakerfritz · 1st February 2012, 08:14 PM

Quote:

Originally Posted by jerrynsr

Swap the Power Tube that sparked to the other channel. See if the hum moves with the tube. I had a defective 12AX7A, one filament was really bright. I had a hum that was uneffected by volume control so I figured the hum was getting picked up from the ac filament voltage. I moved the tube and the hum went with it. Now I have some vintage NOS preamp tubes on the way.

did you noticed the thread is three years old?

jerrynsr · 2nd February 2012, 12:58 AM

lmao... Ok I guess someone can learn from the thread.

14th December 2009, 08:08 PM	#1
gurley123 diyAudio Member Join Date: Oct 2007	Help please, Jolida 202a hum. This may be futile but i need to give it a shot. I need some help chasing down some hum in my amp. This hum appeared about three weeks ago in my up-to-now very quiet Jolida 202a. The hum appears to be independent of volume setting or source selection. It's fairly low level but loud enough for me to hear in the quieter passages of music. I've owned this amp for about 16 years now and this is the first bit of trouble I've had with it. Right around the time the hum showed up, I had a power tube spark on me. I think I had let the bias drift to far and that is what caused the sparking. I had heard some static right before the sparks but I thought it was in the program I was watching(my amp is not in my line of sight.) After sparking, the tube still appeared to be sealed and after biasing behaved reasonably well (it was a little erratic but I kept the multimeter handy and checked it often) but the hum was now present. Four new tubes now and the hum is still there. I have very little knowledge of tube amps other than what I have read (lethal voltages inside!!!, it might not be that hard to change it to triode, ect.) and I know that tracking down hum problems are tricky in the first place but I thought I would ask for some help here. Maybe there's a simple fix for it (I'm not holding my breath.) I would like to thank you in advance for just coming here and reading my post and will get the wife to bake you up some awesome cookies if you can help my exorcise my noisy demon.

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14th December 2009, 09:15 PM	#2
StephenJ diyAudio Member Join Date: Dec 2009 Location: Glasgow, Scotland	Dear gurley123, May I ask your help. I am new to the site and despite searching have failed to find. How did you make your post? Having given the details and asked the questions how did you post/get it put up on the site? Sorry if am a burden but would be very greatful for your help. In hopeful anticipation, thanks! StephenJ

24th January 2012, 05:29 PM	#3
jerrynsr diyAudio Member Join Date: Sep 2011	Swap the Power Tube that sparked to the other channel. See if the hum moves with the tube. I had a defective 12AX7A, one filament was really bright. I had a hum that was uneffected by volume control so I figured the hum was getting picked up from the ac filament voltage. I moved the tube and the hum went with it. Now I have some vintage NOS preamp tubes on the way.

2nd February 2012, 12:58 AM	#5
jerrynsr diyAudio Member Join Date: Sep 2011	lmao... Ok I guess someone can learn from the thread.

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