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Kalamazoo Reverb 12

412 Views 9 Replies 5 Participants Last post by  Alan Small
1967 model, all original

arrived with a terrible loud humm that made it unplayable

I started with replacing the two cap cans which brought to usable(just a wee bit o hum hiding back there) territory again.

three prong completed

100R heater humm balance to ground(after I have exhausted necessary fixes I may float the circuit on a raised voltage platform or the cathode of one of the power tubes, instead of ground, which can result in quieter operation).

While cleaning the entire unit i discovered some hippy had glued fluffy pillow stuffing onto the speaker cone馃お

New wgs ceramic installed delivers a good sound with a bit of balls if asked.

I have cleaned and serviced all contacts.

Next step is to consider each resistor and capacitor one at a time, replacing where required, especially in the trem circuit which is weak.

New tubes also in the mix.

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Removed this length of coiled wire from the rotary on/off switch(which is also the treble cut) because wall voltage running along beside the preamp pots n wires promises oddball noises.

New on/off beside fuse and pilot.
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Replaced the less than ideal input circuit with a useful princeton version and adjusted the first triode into a typical fender design...voila...louder, clearer, more headroom. Now one input is quieter than the other and both of them are louder than the original and seem to be of higher fidelity(more lows, more highs, no mud).

the original inputs sounded equal in volume and seemed be of low fidelity

Replaced the trem caps with .047 instead of .01 and .02 ... et voila...tr茅molo frais, profond et luxuriant


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Found the volume pot was not grounded(had a couple ohms showing on the meter between main ground and pot housing) as well as the others(zero ohms)..pulled it and removed the paint from the chassis around the hole then freshly installed...resulted in less background humm which is part-n-parcel

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Back together and performing well.
I will play her for a few hours thursday night at a gig and perhaps will determine if a voicing adjustment is needed(this cant really be discovered alone in a room of a house) the band must be in situ
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The amp performed well in a fairly loud rock setting in a barn with keys, bass, two guitars and a deaf drummer 馃お

It shall stay as is and will make the rounds to a few gigs til someone snaps it up.

Next up is a 67 Traynor yba 2b with 6v6s that is intermittent signal
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