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Post subject: Noisy blackface
Posted: Sat May 29, 2010 3:28 pm
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Hey y'all. I've got a 50 watt '65 Blackface AA165 Bassman head and it is making some heinous noise when I turn it up over about 1-1/2 in either the bass instrument or normal channel. Any suggestions? A friend said something about replacing all the 100k resistors in the preamp section but I thought I'd verify with some experts first. :?:

The serial # on the amp is A08662 and the date code is OG


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Posted: Sat May 29, 2010 5:22 pm
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Hi there, Rattle and welcome to the forum. Guess we'd need to know what kind of noise you're getting(crackling, popping, static, ringing, etc.) Also, whether or not a guitar is plugged into the amp? The tubes condition would usually be the first thing to consider, and whether or not they are getting a good clean contact in their sockets. Art

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Posted: Tue Jun 08, 2010 5:06 pm
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Sorry it took so long to get back. Road work ya know?

Okay, so the noise only happens when the guitar is plugged in. It happens on both channels and both inputs on each channel. It sounds like there is a short. It is a short burst of loud buzzing and it happens intermittently. Hard to explain. Does that help any?


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Posted: Wed Jun 09, 2010 3:20 am
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I suppose that this guitare is working fine in other amp with the SAME guitar wire ? No noise ?

By the way I think this amp have no more than 40 watts.

aclempoppi, bad ground contact in all the amp input jacks, between guitar wire and input jacks ?


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Posted: Wed Jun 09, 2010 5:16 am
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The AA165 Bassman is rated at 50 watts
Here's the specs and schematic http://www.ampwares.com/amp.asp?id=27
I agree with Art. Tube sockets and jacks may need cleaning and the sockets may need to be re-tensioned. Could also be a bad tube. Has your amp ever been recapped?

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Posted: Wed Jun 09, 2010 7:28 am
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Yeah, I use the same guitar and cable in another amp and they work just fine. I put in new tubes all around, however I didn't clean the sockets. I'll try that. I don't think the amp has been recapped... what is that?

Supro, how do I re-tension the sockets?

Oh and it is rated at 50 watts and it's the loudest 50 watt amp I've ever heard.

Thanks for the response guys.



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Posted: Wed Jun 09, 2010 7:56 am
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All amps operate on DC voltages -- thus it is necessary to convert the AC current from your wall socket in order for the components within the chassis to function. This conversion process occurs in the amp's power supply, beginning with a rectifier (either tube or solid-state diode). The output voltage is then passed through a bank of capacitors which filter out any remaining AC "ripple" in order to prevent the amp from internally generating noise which will audibly present itself at the output transformer. These "filter caps" are perhaps the hardest-working individual components in an amp and require routine replacement for optimum performance. Likewise there is a filter cap in the biasing circuit which should be replaced as often as the primary filters. There's no hard-and-fast rule about the replacement interval......I've seen filter caps last thirty years. OTOH, I've seen some begin to bulge and leach electrolyte from their casings in as little as ten. My personal protocol is: inspect every five years, replace at ten regardless of visual condition.

HTH


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Posted: Wed Jun 09, 2010 8:26 am
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Retroverbial wrote:
All amps operate on DC voltages -- thus it is necessary to convert the AC current from your wall socket in order for the components within the chassis to function. This conversion process occurs in the amp's power supply, beginning with a rectifier (either tube or solid-state diode). The output voltage is then passed through a bank of capacitors which filter out any remaining AC "ripple" in order to prevent the amp from internally generating noise which will audibly present itself at the output transformer. These "filter caps" are perhaps the hardest-working individual components in an amp and require routine replacement for optimum performance. Likewise there is a filter cap in the biasing circuit which should be replaced as often as the primary filters. There's no hard-and-fast rule about the replacement interval......I've seen filter caps last thirty years. OTOH, I've seen some begin to bulge and leach electrolyte from their casings in as little as ten. My personal protocol is: inspect every five years, replace at ten regardless of visual condition.

HTH

+1
You can use a dental pick to tighten the tube sockets. You'll need to discharge the capacitors. There are potentially lethal voltages in there even with the amp unplugged.
What I would do with an amp of this age is take it to a qualified amp tech and have him/her go over it. Even if the electrolyte doesn't leak out of the caps it can dry up. Sounds like it's due for some routine and well deserved maintenance.

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Posted: Wed Jun 09, 2010 8:53 am
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63supro wrote:
Retroverbial wrote:
All amps operate on DC voltages -- thus it is necessary to convert the AC current from your wall socket in order for the components within the chassis to function. This conversion process occurs in the amp's power supply, beginning with a rectifier (either tube or solid-state diode). The output voltage is then passed through a bank of capacitors which filter out any remaining AC "ripple" in order to prevent the amp from internally generating noise which will audibly present itself at the output transformer. These "filter caps" are perhaps the hardest-working individual components in an amp and require routine replacement for optimum performance. Likewise there is a filter cap in the biasing circuit which should be replaced as often as the primary filters. There's no hard-and-fast rule about the replacement interval......I've seen filter caps last thirty years. OTOH, I've seen some begin to bulge and leach electrolyte from their casings in as little as ten. My personal protocol is: inspect every five years, replace at ten regardless of visual condition.

HTH

+1
You can use a dental pick to tighten the tube sockets. You'll need to discharge the capacitors. There are potentially lethal voltages in there even with the amp unplugged.
What I would do with an amp of this age is take it to a qualified amp tech and have him/her go over it. Even if the electrolyte doesn't leak out of the caps it can dry up. Sounds like it's due for some routine and well deserved maintenance.


I agree. Sounds like it is time for a good cap job, retention, jack cleaning and so forth. Do you have a good local tech?


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Posted: Wed Jun 09, 2010 9:08 am
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Yeah, I think having a pro look at it is my best bet. I got a guy but he's slow. Anybody have any good recommendations for a tech in Denver?


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Posted: Wed Jun 09, 2010 12:55 pm
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retelltrap you are right it is 50 watts amp, sorry.

By the way I have two Bassman blacface here that I just finish to repair.

On both is write in the cabinets (on the sticker) AA165 but the frame , electronic are AB165.
One is a 1965 and the other is 1966. I read there are a lot of mischmatch between cab and chassis on those first years with CBS.


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Post subject:
Posted: Thu Jun 10, 2010 11:35 pm
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That amp is kind of interesting, in that both pre amp channels run through V2(7025). And of course, both channels share the phase inverter, V4(12AT7). I think I'd try swapping out those tubes before sending it off. Just trying to find a component that would affect all four inputs. Art

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Posted: Fri Jun 11, 2010 5:25 am
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stratele52 wrote:
retelltrap you are right it is 50 watts amp, sorry.

By the way I have two Bassman blacface here that I just finish to repair.

On both is write in the cabinets (on the sticker) AA165 but the frame , electronic are AB165.
One is a 1965 and the other is 1966. I read there are a lot of mischmatch between cab and chassis on those first years with CBS.

I've read that too,that was a thing that most people wouldn't notice...you must know your amps good stratele. :)


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Posted: Fri Jun 11, 2010 6:33 am
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Rebelsoul wrote: "I 've read that too,that was a thing that most people wouldn't notice...you must know your amps good stratele. "

Yes Rebelsoul
I repair many amps and I have all schematics so I see those AA165 are not AA165 schematic but AB165.
It's very different amp /circuits.


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Posted: Fri Jun 11, 2010 8:22 am
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aclempoppi wrote:
That amp is kind of interesting, in that both pre amp channels run through V2(7025). And of course, both channels share the phase inverter, V4(12AT7). I think I'd try swapping out those tubes before sending it off. Just trying to find a component that would affect all four inputs. Art


Yeah, I changed out the tubes and that did not eliminate the problem.


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