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Topic: Blue Tube 904 on the fritz |
Jerry Overstreet
From:
Louisville Ky
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Posted 6 Mar 2007 11:25 pm |
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A shot in the dark maybe, but I know there are a lot of electronics experts here. Ken Fox, Brad Sarno, Bill Crook, et al.
I have a TubeWorks 904 unit with master, gain, eq, contour and bias controls. I use it for guitar with an old Silvertone 1482 that has virutally no tone control, so this unit works great for tone shaping as well as getting the gain up to a usable level.
Lately, I get an intermittent crackling and oscillating noise from it. It's like a ping pong effect that starts slow and gets faster. Sometimes no sound at all. I know it is the unit as it works fine in bypass mode.
I have several pieces of the BK Butler Tubeworks stuff and I know that there are problems with the control pots sometimes, but I'm pretty sure that is not the problem here.
Changing out the preamp tube is no help either. I'm seeing a couple filter caps I guess, having values of 2200 uf. Could one of these be going bad?
Any ideas? I don't really want to spend a lot on it, OTOH it's become an essential tool for my guitar sound. All input welcomed and appreciated. JO. |
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Ken Fox
From:
Nashville GA USA
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Posted 7 Mar 2007 5:17 am
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I would check the caps for DC leakage. I finally broke down and bought a nice ESR (equivalent series resistance) meter just for testing leaky caps. I have several cap checker and this is the real ticket for my shop! As I do a lot of old tube amps it will be great.
I can now test caps in circuit with a high degree of accuracy. I check some filters yesterday in a N-400 and found they were leaky and had dropped from 4700uf to around 1700uf.
Without one your best test is a DC meter to see if there is DC on the output side of the audio coupling caps and tone caps. Even a 1/2 volt of leakage can upset bias and cause strange noises to emit from the amp.
I recently had a Fender Super Reverb in with noises like you are having. All but 1 of the film caps were leaking! The amp was pristine looking inside. I would not have suspected such problems. It had more noise than I had ever heard from a Fender amp. Must have been a bad run of caps that day! |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 7 Mar 2007 8:40 am
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| My guess would be a bad bypass cap. Those are electrolytics, like those in the power supply, but smaller in size and value. When they begin to go bad, they can cause all kinds of strange noises. |
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Jerry Overstreet
From:
Louisville Ky
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Posted 11 Mar 2007 7:07 pm thanxalot
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'Preciate the input guys...apologies for the tardy Thank You.
FYI [those not familiar w/this unit], it is a 90's vintage rack mount tube enhancer/preamp unit originally designed for bass, but works well for calmer blusey overdrive tones on guitar as well.
I'll be in touch if anyone feels like troubleshooting and repairing this unit. E/m me if any interest and many thanks. JO. |
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