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Post subject: 1976 Silverface Bassman 50 Pop and Hum
Posted: Mon Sep 10, 2012 1:51 pm
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I have an issue with my 1976 master volume bassman 50.

Firstly when I take my amp off Standby, I get a bassy punchy/pop sound. The right power tube flashes blue when this occurs.

Secondly, when the amp is on there is a hum.

In a 5 day period since these issues began it sounds the amp has lost power and is distorting at low volumes. When I look at the tubes, they are still lit up orange like normal.

Can anybody suggest what the issue might be and if there are parts I can order and replace myself without spending hundreds of dollars on repairs? Thank you kindly in advance.


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Post subject: Re: 1976 Silverface Bassman 50 Pop and Hum
Posted: Mon Sep 10, 2012 2:00 pm
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Location: Tombstone Territory
The hum is likely the result of aging electrolytic caps under the doghouse. These always require periodic replacement -- every ten or fifteen years, depending upon the quality of the replacements. Cost in parts, roughly $85. The filter cap in the bias-balance circuit should be simultaneously supplanted as well -- about ten or fifteen bucks. There are some 1-watt power-rail resistors beneath the doghouse which should be inspected and, if needed, replaced too.

Bad filter caps *may* also be the cause of your "pop" when coming out of standby into the play mode.

HTH

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 1976 Silverface Bassman 50 Pop and Hum
Posted: Wed Sep 12, 2012 2:29 pm
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If the hum is the same at any volume , it is a filter capacitor . If more volume more hum ,it is not a filter capacitor. Check tubes.

Old and defective power tube can hum . If you loose power, chance are the power tubes and Phase Inverter tube needed to be replaced with a bais check for power tube.

Better to find a good tech , not anybody in local music store. This amp could need a good tune-up by a professional.


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Post subject: Re: 1976 Silverface Bassman 50 Pop and Hum
Posted: Wed Sep 12, 2012 4:35 pm
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Location: Tombstone Territory
stratele52 wrote:
This amp could need a good tune-up by a professional.


My thoughts as well.

Durable as they are, the original Fender amps still require periodic maintenance to perform at their best.

Rawk on!

8)

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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