CHAMP ELECTRONICS -" THE VALVE AMP HOSPITAL"

NOTTINGHAM, ENGLAND

 

REPAIR OF A FENDER MUSICMASTER BASS COMBO AMPLIFIER





"Hey everyone - not too many of these have crossed my path! A Fender Musicmaster Bass Combo. Actually as a bass amp, I think a bedroom is about as far as it gets! Anything further than that and I think that it would be an absolute joke! As a bass amp I can only say that this is a disgusting thing! Absolutely full of "farts and buzzers". However if used on guitar, than it at least stands a chance. It was brought to me by my friendly metalwork man (Steve) with a request to "sort it out" as he had just bought it and it sounded dreadful.

As one of the 6V6's didn't even light up and the other was about 50% down, it's of no wonder it sounded like it did! After a new set of output tubes it did in-fact work, but still not satisfactorily and with a horrible gritty buzz when the volume was turned up too? More lift of the volume also saw it going into some kind of strange paralytic oscillation.

As I later found out this amp had been very damp (the story of my life with people leaving delicate electronic equipment in damp places such as garages etc!). The main trouble with "damp Fenders" is that the compressed, waxed component boards that they used for many years, after much use and heat (especially as most of them are an upside-down mounted chassis) causes the waxed board to slowly melt. This now leaves the board(s) susceptible to damp/moisture exposure and eventually leads to "tracking" of various kinds between valve (tube) stages. This was the problem with this example too. The only way around this was to remove the board completely and replace it with a "hand wired" tag board instead. On doing so, the problem disappeared completely, and in-fact you couldn't even hear the amp switched on; even with ones head in the speaker!

I used all new resistors and most of the original caps (which were all tested as OK). After a minor component change of the input cap, which filtered out most of the lower frequencies (- undoubtedly a Fender design to "cover their asses" as being advertised as a "bass amplifier?"), on six string guitar she sounded good and full of tone.

Steve was well pleased with the results to say the least.

Your interest is gratefully appreciated. 

- John"







The old board, effected by damp.









The new board.






The new board in position.










 

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