Amp Issue

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thebends9
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Amp Issue

Post by thebends9 »

Have a lead on an older amp with a buzzing issue; Guy states the following:

I can best describe it as a low end buzz that changes pitch with the notes you're playing. mostly on lower notes but not the same weird buzzing sound that a blown speaker gives off.

Any idea what this could be?
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jerms
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Re: Amp Issue

Post by jerms »

filter caps...
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thebends9
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Re: Amp Issue

Post by thebends9 »

Thats what I was afraid of. He thought it might be his tubes
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HorseyBoy
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Re: Amp Issue

Post by HorseyBoy »

I get this occasionally on my 1970 VibroChamp, a buzzy, distorted sound when you're fretting the bass strings, especially the bottom E, even though I've replaced the filter caps. Bugs the shit out of me because it doesn't happen all the time.
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waveclipper
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Re: Amp Issue

Post by waveclipper »

Filter caps most likely but still might be a voice coil rub, dodgy tube or possibly parastics? I've no doubt any decent tech with an oscilloscope could have that sorted very fast. Fear not - filter caps would be a cheaper fix than decent tubes!
HorseyBoy wrote:I get this occasionally on my 1970 VibroChamp, a buzzy, distorted sound when you're fretting the bass strings, especially the bottom E, even though I've replaced the filter caps. Bugs the shit out of me because it doesn't happen all the time.
You might be able to stiffen up the power supply of your Vibrchamp just enough to get rid of that horseyboy? Maybe just increasing the first filter cap to 22uF might be all that it takes - shouldn't make any major tonal differences and a 5Y3GT should be able to handle it no bother.
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Laundromat
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Re: Amp Issue

Post by Laundromat »

HorseyBoy wrote:I get this occasionally on my 1970 VibroChamp, a buzzy, distorted sound when you're fretting the bass strings, especially the bottom E, even though I've replaced the filter caps. Bugs the shit out of me because it doesn't happen all the time.
Did you change the bypass caps as well? I had a 1970 Champ that developed this fizzy buzzing that would ride on top of the notes and changing out the waxy bypass caps fixed it.
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charge
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Re: Amp Issue

Post by charge »

Sounds like the issue I had with my 67 Vibro Champ. A new speaker resolved it.

HorseyBoy wrote:I get this occasionally on my 1970 VibroChamp, a buzzy, distorted sound when you're fretting the bass strings, especially the bottom E, even though I've replaced the filter caps. Bugs the shit out of me because it doesn't happen all the time.
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PlumCrazy
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Re: Amp Issue

Post by PlumCrazy »

HorseyBoy wrote:I get this occasionally on my 1970 VibroChamp, a buzzy, distorted sound when you're fretting the bass strings, especially the bottom E, even though I've replaced the filter caps. Bugs the shit out of me because it doesn't happen all the time.
And replacing the filter on a VC is a pain in the ass. The speaker on my 74 sucked big time.
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HorseyBoy
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Re: Amp Issue

Post by HorseyBoy »

Thanks for the advice, guys. I'll crack it open and check it out on the weekend.
It did occur to me that it might be the speaker, but the speaker was replaced (with a Jensen P8R) before I got the amp and I figured it would be okay. I'll try running it through a cab to make sure. But I might start hunting for a vintage replacement anyway, just to be sure. :tu:
Here's a pic of the guts last time I worked on it:

Image

(Click through for a full-size shot.)

Replaced the cap can, removed the “death cap”, replaced the electrolytic caps with the Spragues and tone of the resistors (the 460/1 watt). If anyone spots a dodgy solder joint, let me know!
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waveclipper
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Re: Amp Issue

Post by waveclipper »

Either of you got things sorted yet?

I'm thinking you might need a buddy with an oscilloscope at this stage Horsey?
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