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Post subject: Fender Musicmaster Bass amp buzz - help!
Posted: Sun May 11, 2014 1:19 pm
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Hello, this is my first post i'm new!

I recently bought a Fender Musicmaster Bass amp second hand. I was told it had a buzz, the guy who sold it to me knew very little about the amp and just wanted rid of it.

I've read a couple of things that said it may be the tubes or the filter cap (or it could be something worse). I've replaced all the tubes (6v6 x2, 12ax7) but don't know where the filter cap(s) are. I've uploaded some gut shots and a video of the hum (hum starts at about 25 seconds in). It gets louder when the volume is turned up and the tone pot affects it too.

any advice would be great! I'm handy with a soldering iron so if it's just replacing capacitors I should be ok as long as I know which ones it is and what would be best to replace them with!

Photos via flickr
https://www.flickr.com/photos/117414543@N02/14183022493/in/set-72157644213108840

Video via Vimeo
https://vimeo.com/94867812

or Video via YouTube
https://www.youtube.com/watch?v=RHMoTHt3we8

thanks! - electrafrench


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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Sun May 11, 2014 3:24 pm
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Welcome to the forum. You got a Pretty clean amp. Everything looks original which means it is well past time for it to go to a qualified tech. Amps contain enough voltage to Kill You! It is NOT a matter of being handy with a soldering iron. Also replacing the power tubes means you also need to rebias them, again another thing a qualified tech should do.

T2

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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Sun May 11, 2014 4:46 pm
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T2Stratman wrote:
Welcome to the forum. You got a Pretty clean amp. Everything looks original which means it is well past time for it to go to a qualified tech. Amps contain enough voltage to Kill You! It is NOT a matter of being handy with a soldering iron. Also replacing the power tubes means you also need to rebias them, again another thing a qualified tech should do.


+1

Find yourself a competent tech and pay him exorbitant sums to return your amp to factory specs or risk blowing it to smithereens and/or turning yourself or some vital body part into a crispy critter.

It's as simple as that.

Arjay

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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Mon May 12, 2014 1:33 am
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I know how to drain the filter caps etc. so I don't fear the electric-boom (the things you learn *after* opening up a plugged in watkins copicat)

I was more wondering if their was any advice or caps that are likely to be done so i could try replacing them without having to pay huge amounts of cash to someone to look it over, then even more money if they have to actually replace anything.

or any advice on this particular hum would be great too.

like I said if needs must i would take it to a tech but I am also eager to learn!

cheers


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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Mon May 12, 2014 1:53 am
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Here's the schematic......

http://ampwares.com/schematics/musicmaster_bass.pdf

It's a pretty rudimentary design with the exception of the center-tapped tranny performing the role of a conventional dual-triode phase inverter. There are three filter caps, two cathode bypass caps, and one bias supply cap -- all of them electrolytics and all of them likely ripe for replacement (an aging filter cap is probably responsible for that annoying buzz). Note that these caps are polarity-specific. While you're in there rooting around you can ditch the death cap -- with a grounded 3-conductor power cable it was never really necessary to begin with. The bias supply is fixed so if new power tubes are part of the plan be sure to order a matched pair.

Arjay

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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Mon May 12, 2014 1:57 am
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Noise : Could be the filter caps and / or tubes.

Unmatched output power tubes can make noise , if one is weak .

Filter caps ; the big brown cylinder , the big silver cylinder .

Other small silver cylinder ( 3 ) are like filter caps and may need to replace also.


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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Mon May 12, 2014 2:17 am
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that's great guys! any tips on what sort of quality capsI should be ideally using?

I bought matched tubes to replace the ones in it, though its exaclty the same buzz with the old tubes as it is with the new tubes.


thanks!


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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Mon May 12, 2014 2:24 am
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F&T caps are very good ;

http://www.tubesandmore.com/products/ca ... nd%3DF%26T

Sprague too ;

http://www.tubesandmore.com/products/ca ... gue%20Atom


I use both.


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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Mon May 12, 2014 2:37 am
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+1 on the F&T's.

I'm no longer so trusting of the Sprague's .

:(

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: Fender Musicmaster Bass amp buzz - help!
Posted: Mon May 12, 2014 2:45 am
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Retroverbial wrote:
+1 on the F&T's.

I'm no longer so trusting of the Sprague's .

:(

Arjay


yeah i've seen a lot of people complaing of either poor quality Sprague caps or fake ones!

thanks again guys!!


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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Mon May 12, 2014 2:54 am
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electrafrench wrote:
Retroverbial wrote:
+1 on the F&T's.

I'm no longer so trusting of the Sprague's .

:(

Arjay


yeah i've seen a lot of people complaing of either poor quality Sprague caps or fake ones!

thanks again guys!!



I read one or two but I have no opinion about that . I read so many thing on the web........

I never had any problem with any Sprague bought from honest store .


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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Mon May 12, 2014 3:31 am
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F&T is the way to go. The Fender Musicman Bass amp seems to have three main power supply filter caps. They are OEM 20mfd/350VDC rated caps. For this amp, and any 6V6GT amp, I would go to higher voltage rated main PSU caps.

F&T 22mfd/500VDC will prolly fit fine in your amp. One appears to be sitting on the circuit board. The other two are prolly closer to the PT(?). .

http://www.tubesandmore.com/products/C-ET22-500-FT


You should replace the 25mfd/25VDC electrolytic cap that ties the cathode of the 6V6GT tubes to ground. Use a 25mfd/50VDC rated electrolytic cap. Plus, I'd change the 220 ohm, 2 watt CC resistor paralleling this bypass cap, too. These resistor and bypass cap sets the bias on the 6V6GT's (this is a cathode-biased amp). I'd use a good wire-wound ("sandbox" style resistor is fine), 250-ohm, 5-watt will work well.

http://www.tubesandmore.com/products/re ... 3D5%20Watt


You should be good to go, after these replacements. You may want measure the idle bias of the 6V6GT's. They are in Class "A," push-pull mode. With 290VDC on the plates, readings should be around 28-32mA per tube for 75-80% of max idle dissipation per tube. HOWEVER, there is not the real worry about idle bias, such as in other fixed-bias Fender amps. Provided are components in the output stage are within OEM tolerance.

Amps that are cathode-biased have a self-leveling bias, to a degree. As long as the cathode resistor is within tolerance and is stable under heat and the bypass cap is fresh --- a fresh matched pair of 6V6GT's should be fine. They will self-level to an idle bias, depending on the strength of the tubes and the stability of the circuit around them. This is why no one checks the idle bias of 12AX7 or other signal tubes. These tubes are set in Class "A" single-ended mode (99% of the time, in guitar amps).


Good luck with your amp! Keep us in the loop. :mrgreen:

http://bmamps.com/Schematics/fender/mus ... _schem.pdf


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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Mon May 12, 2014 9:37 am
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stratele52 wrote:
electrafrench wrote:
Retroverbial wrote:
+1 on the F&T's.

I'm no longer so trusting of the Sprague's .

:(

Arjay


yeah i've seen a lot of people complaing of either poor quality Sprague caps or fake ones!

thanks again guys!!



I read one or two but I have no opinion about that . I read so many thing on the web........

I never had any problem with any Sprague bought from honest store .


In that case, enjoy your Sprague's -- I'll never use them again.

Arjay

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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Mon May 12, 2014 10:55 am
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Retroverbial wrote:

In that case, enjoy your Sprague's -- I'll never use them again.

Arjay



+1 :lol:


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Post subject: Re: Fender Musicmaster Bass amp buzz - help!
Posted: Mon May 12, 2014 5:48 pm
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stratele52 wrote:
Retroverbial wrote:

In that case, enjoy your Sprague's -- I'll never use them again.

Arjay



+1 :lol:


+2...my amp tech only uses F&T's and will only put in Sprague's if the client insists and he flat refuses to use Illinois'!

T2

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