# hum in Fender Bassman



## mario (Feb 18, 2006)

I have a '62 Bassman head and it has recently started to produce a hum. It does not get any louder if I turn up the volume or quieter if I lower the volume. I also hear the hum if I pull out my guitar cord. Any ideas what this might be before I bring it in would be great.


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## Ripper (Jul 1, 2006)

mario said:


> I have a '62 Bassman head and it has recently started to produce a hum. It does not get any louder if I turn up the volume or quieter if I lower the volume. I also hear the hum if I pull out my guitar cord. Any ideas what this might be before I bring it in would be great.


Has the amp ever been recapped? Chances are you've got a cap or caps that need replacing.


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## Wild Bill (May 3, 2006)

mario said:


> I have a '62 Bassman head and it has recently started to produce a hum. It does not get any louder if I turn up the volume or quieter if I lower the volume. I also hear the hum if I pull out my guitar cord. Any ideas what this might be before I bring it in would be great.


Yeah, Ripper's right. I'll bet two beer that the filter caps are original and need to be replaced. 

Considering that they were only expected to last 10-15 years I don't think they owe you anything.:smile:

Take it to a good tech and it's a routine job. Then it will be good for another bunch of years!

:food-smiley-004:


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## mario (Feb 18, 2006)

Thank you for the replies guys. I figured it might be something like that.


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## mario (Feb 18, 2006)

Another question guys. A fine fellow Forum member PMed me that he has a pre-built filter and bias board loaded with Spragues-Atom caps. It was to have been used on a Silverface Bassman, but he has since sold the head. My question...will it work in my Brownface Bassman? He's not sure himself, so I figured I would pick your brains.

Thank's in advance!


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## Ripper (Jul 1, 2006)

mario said:


> Another question guys. A fine fellow Forum member PMed me that he has a pre-built filter and bias board loaded with Spragues-Atom caps. It was to have been used on a Silverface Bassman, but he has since sold the head. My question...will it work in my Brownface Bassman? He's not sure himself, so I figured I would pick your brains.
> 
> Thank's in advance!


I'll have to dig out the schematics but I don't think so. If memory serves me right, your blonde bassman uses 5 20Uf caps and the silverface use 3 20's and 2 70's or 40's. The bias circuit is different in the blondes as well. Changing the caps out on your amp is an easy job for a tech.

Just our of curiousity, what is the circuit model of your amp? (It should say on the tube chart). With your's being a 62, it could be one of two versions that were out at the same time. Does your have a rectifier tube?


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## Adicted to Tubes (Mar 5, 2006)

Your bassman is likely a model 6G6 or 6G6A and they take all 600v filter caps in parallel.Since it is almost impossible to find 600v filter caps these days it is best to modify the filter cap board to a later Fender arangement where the first two filter caps are wired in series for a voltage rating of 700v or more.This requires a pair of 220k decoupling resistors.
As long as your friend knows how to wire it in,the silverface board will work.

www.claramps.com


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## Ripper (Jul 1, 2006)

Get your tech to check the values of the original caps. From having worked on as many old fenders as I have over the years, what the schematic says is in there and what it really left the factory are sometimes different. I've recapped lots of old blondes and browns that shipped from the factory with 500 or 550 volt caps in them. The voltages in those amps usually run in the 425-450 range. 

Like addicted to tubes said you could modify the silverface board, but you can still get 600v electrolytics. Newark sells them http://www.newark.com/jsp/search/br...ch_001&Ntt=electrolytic&Ntx=&_requestid=52913.

The trouble with using caps in series is depending on the physical size of the caps, sometimes you can get them to fit into you cap can.

I've had good luck using computer grade 500 volt caps. They are a 600v surge and are easy to find and reasonable priced. It was an old fender amp tech from LA that put me onto these. I've got them a fair amount customers blonde and brown amps that are regularly gigged and they have never given a problem.


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## mario (Feb 18, 2006)

Ripper said:


> I'll have to dig out the schematics but I don't think so. If memory serves me right, your blonde bassman uses 5 20Uf caps and the silverface use 3 20's and 2 70's or 40's. The bias circuit is different in the blondes as well. Changing the caps out on your amp is an easy job for a tech.
> 
> Just our of curiousity, what is the circuit model of your amp? (It should say on the tube chart). With your's being a 62, it could be one of two versions that were out at the same time. Does your have a rectifier tube?


Hey guys,

Thank's for the replies! My Bassman head is a 6G6-B and yes, it does have a tube rectifer. LOL, now I have to find a tech here in London! Pickings are very slim here. The last time I had amp problems (a different one), I had to send it to Toronto.


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