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Post by jkramsey1991 on Jun 11, 2017 7:24:00 GMT -7
Got a 72 Bassman 50 recently picked up. She was making some noises before that im relatively sure was plate resistors. Me and my friend went through and replaced filter caps, plate resistors, and black faced the phase inverter.
Cranked it up and with the volume at 6 or higher it gets a nasty sounding sputtering type distortion. Really harsh sounding not musical what so ever. We have tested everything we can think of reflowed solder joints did the chopstick test to no avail and tried a different set of power tubes as well as changed all preamp tubes and it persists.
Any ideas of what could cause something like this?
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Jair Yess
Junior Member
Doctor doctor give me the news, I Got a bad case of loving you
Posts: 66
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Post by Jair Yess on Jun 11, 2017 11:16:28 GMT -7
Is your B-man equiped with grid resistors? If not check the screen resistors (470R). Did you check the bias capacitors for leakage? Did you check the PI load resistors? 82k and 100k? Watch out with those Bassman (or every Fender eyelet board for that matter) circuit boards, eyelets tend to moisten up and take too much solder....
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Post by jkramsey1991 on Jun 11, 2017 12:07:48 GMT -7
We replaced all bias caps and screen resistors when we were servicing it. Grid resistors were also replaced as well. It's a super strange noise. Sounds like a speaker getting ready to blow but I've tried three different cabinets the lowest rated one was rated at 100 watts. Same noise through my twin cabinet which has 2 150 watt Eminence speakers.
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Post by Maddog on Jun 11, 2017 14:37:47 GMT -7
Wow....seems like you've checked/rechecked everything.... It makes me wonder if one of the replacement components might be defective....
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Post by Maddog on Jun 11, 2017 14:41:37 GMT -7
Being an older amp, (and since you've checked the routine causes) just to be thorough, you might try double checking the input jacks. I've had them go bad in some of my 50's tweeds and really make some crazy noises that were very difficult to track down. Good luck...
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Post by zpilot on Jun 11, 2017 20:40:35 GMT -7
And proper grounding. The pots and input jacks are grounded to that copper plate inside the chassis. Sometimes corrosion develops between those connections and you can get parasitic oscillations.
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Post by jkramsey1991 on Jun 12, 2017 2:49:58 GMT -7
I'm going to check all the grounds. Since how it has to be cranked to make the noise it makes me suspect something is not connected well. I've chopsticked the crap out of it but can't replicate it at lower volumes.
Also going to pick up some deoxit and clean the crap out of the preamp sockets too
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Post by zpilot on Jun 12, 2017 3:27:32 GMT -7
Also try replacing the coupling caps to the output tubes. Especially if they are the infamous "dog turds".
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Post by jkramsey1991 on Jun 13, 2017 16:24:29 GMT -7
Might have located the problem. Found a pair of old carbon comp resistors near the first set of plate resistors that will pop and hiss loudly when tapped from one side. Got some replacements coming going to replace all of the carbon comps in that region to be certain
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Jair Yess
Junior Member
Doctor doctor give me the news, I Got a bad case of loving you
Posts: 66
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Post by Jair Yess on Jun 18, 2017 2:37:44 GMT -7
Might have located the problem. Found a pair of old carbon comp resistors near the first set of plate resistors that will pop and hiss loudly when tapped from one side. Got some replacements coming going to replace all of the carbon comps in that region to be certain Any luck fixing your B-Man?
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Post by jkramsey1991 on Jun 19, 2017 3:06:07 GMT -7
Nope noise is still there. Taking it to David Allen today. It's beyond my diagnostic capability
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Post by zpilot on Jun 19, 2017 3:28:50 GMT -7
Nope noise is still there. Taking it to David Allen today. It's beyond my diagnostic capability Please let us know how it comes out.
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Post by jkramsey1991 on Jun 19, 2017 7:22:16 GMT -7
Will do guys. I'm suspecting it's something in the power supply or at least power section. But I don't know how to diagnose it accurately. But I'm sure someone like David Allen can and since he's only 25 minutes away from the office seems logical to have him take a looks
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Post by jkramsey1991 on Jun 27, 2017 5:06:15 GMT -7
She's fixed! Of all things it was in the output jack wiring that was causing the noise. He replaced the jacks and rewired and it's all good. I feel like an idiot because I thought I checked that oh well. David also did some checking throughout and replaced a few small components he said had drifted too far out of spec.
Played it for about and hour last night and it sounds great. These old bassmans may be the best kept secret in vintage amps. I plan to add another to my collection this year
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Jair Yess
Junior Member
Doctor doctor give me the news, I Got a bad case of loving you
Posts: 66
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Post by Jair Yess on Jun 28, 2017 10:08:36 GMT -7
She's fixed! Of all things it was in the output jack wiring that was causing the noise. He replaced the jacks and rewired and it's all good. I feel like an idiot because I thought I checked that oh well. David also did some checking throughout and replaced a few small components he said had drifted too far out of spec. Played it for about and hour last night and it sounds great. These old bassmans may be the best kept secret in vintage amps. I plan to add another to my collection this year Get yourself an Antidote if you love the bassman amp, you won't be disappointed!!!
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Post by jkramsey1991 on Jun 28, 2017 10:39:09 GMT -7
Lead me not to temptation! Lol
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Post by Stephen on Jun 29, 2017 6:05:39 GMT -7
I played a 1972 Bassman with 2 x 15" speaker cabinet all through the seventies. Sweet natural tone! I still have it, in fact. But it's just too big for an old man to take anywhere!
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