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i recently came into possession of a 1969 bassman. the amp has a few quirks though, as soon as i take it out of standby it has an occaisonal crackling noise and seems to aways haveafuzzy feedback drone no matter if the instrument is plugged in or not. i tried all channels and it does it on every one so i feel it isnt the input jacks. also when my guitar is plugged in and i turn the volume to about 7 it starts a higher pitch howl. I checked thecaps and they all look recently replaced, and although im no electrician the wiring seems in good shape to me. I was expecting that i am most likely dealing with a faulty tube. also one of mmy transistors is black as usual while the other is an aluminum color. the aluminum one has 606-9-24 stamped on it and the black one i cant really read. anyother ideas? all input is appreciated, thanks
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The black & aluminium "transistors" you refere to are the transformers, Black is the power, aluminium is the output. The code you specify is a product of the 24th week of 1969, made by Schumacher. Sounds spot on.
First thing I would do is try and identify whether the problem relates to something in the preamp/preamp tubes, or later in the circuit. If it is later in thecircuit you need to take the amp to someone.
Looking at the back of the amp's chassis from left to right you have the 2 large glass bottles, the 6L6 tubes. Going further right you now have 4x short metal cylinders, these are the preamp tube covers, they come off with a gentle twist & pull down. With the amp turned off, pull out the preamp tube that is nearest the 6L6s, it is a 12AT7. This will stop the amp from working, but we want to see if it kills the "drone/crackling/howl". If the unwanted noise continues, then this is not a plug in/plug out remedy.
If pulling the 12AT7 preamp tube next to the power tubes kills the unwanted noise, power down, replace the tube, then remove the tube to its right (12AX7, there are 3 of these)...keep going like this until you find a tube, or a position that sticks with the noise. It would be good to have a spare, known good 12AX7 and a 12AT7 on hand to use in this substitution process. -
I planned on having it completely retuned because the person before me put groove tubes in it. I dint really have a way to test it like you said seeing as I don't have substitute tubes and it's not ok to leave one out correct? I'm hoping it's just a tube since that seems cheapest and easiest.. Also about how much does it usually cost to get the amp blackfaced?Comment
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"Blackfacing" means different things to different people. This is an old enough amp where there are not huge differences in tone from the AB763 circuit. The main difference is bias voltage setting (blackface circuit) vs. bias balance (silverface circuit). There are people with preferences for each circuit and there are valid reasons for each.
Speakers will make a lot more difference than Blackfacing. Get the amp working and get to know it a little before you start changing things.
Once you get it running good, dial the volume up to seven and work the hell out of the volume knob on your guitar till you find the sweet spot at the edge of breakup. That's where the magic begins.
There's lots of other fun tricks. Jumper the two channels together with a short patch cord and experiment.
If you do not have a ground prong on your power cord, I would highly recommend changing it out and grounding the chassis to avoid shocking suprises. That's one mod I would do right away.Comment
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I'm taking it to a tech Monday, only have 200$ though so hopefully it won't cost more than that. I opened it up and everything looks really clean and in good shape, do I think th pots and input may have een replaced. The caps are all new and look good so I'm expecting it to be a tube problem. Only issue I myself see is that the first 6l6 tube has a lot of play when plugged in. It wiggled quite a bit and can even turn a bit.Comment
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