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Topic: tube amp noise |
Tommy Boswell
From:
Virginia, USA
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Posted 20 Jun 2013 5:40 pm |
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My Fender Bassman 70 has started making a noise, a low volume irregular squeally-scratchy noise. When I am playing you cannot hear it, but it is loud enough to be annoying when I'm not playing. It's not always there, it comes and goes.
I guess it's time for me to find a good amp tech, but I was wondering if there's anything I can do to trouble-shoot it myself. Could it be a tube going bad? Should I start swapping out tubes one at a time? Has anyone else had this problem?
Thanks in advance for any help from all you electronics gurus. |
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Craig Baker
From:
Eatonton, Georgia, USA - R.I.P.
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Posted 20 Jun 2013 6:21 pm Amp Noise
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Tommy,
You might pull the low-level stage tubes to see if the noise is in the preamp or power stages. It's most likely in a preamp circuit. Nothing beats a spray can of DeOxit D5. Go over all tube pins and sockets, as well as every connector and of course, all of the pots. Beyond this, it's probably a job for a good tech. Hope this is helpful.
Best regards,
Craig Baker
706-485-8792
cmbakerelectronics@gmail.com
C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024 |
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Tommy Boswell
From:
Virginia, USA
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Posted 21 Jun 2013 4:23 am
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| Thank you Craig, I should have thought of that. I have restored several old Peavey SS amps with just a good cleaning of jacks and connectors. I have some Radio Shack electronics cleaner, might give that a try. |
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Chris Boyd
From:
Leonia,N.J./Charlestown,R.I.
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Posted 21 Jun 2013 5:58 am
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Tommy... It is really worth getting some Deoxit D5... works WAY better and is a far better product than the Radio Shack cleaner...Sweetwater Sound has the best price I've found and includes shipping..
_________________
https://www.reverbnation.com/bigredandtheresonators |
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Jack Stoner
From:
Kansas City, MO
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Posted 21 Jun 2013 6:30 am
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I'd try what you have (the Radio Shack) before buying anything else. I'm an ex amp tech and have DeOxit around but I also have some other brands and they have worked as well.
However, it may not be a contact problem. With a tube amp, tubes are always a suspect. |
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Craig Baker
From:
Eatonton, Georgia, USA - R.I.P.
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Posted 21 Jun 2013 8:45 am
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Tommy,
I'll have to go along with Jack. Especially in today's economy. If you already have a can, by all means give it a try. In fact, Radio Shack has a product similar to DeoxIT D5. It's their catalog #64-4345 and also works well. With all of the heat generated by tubes, a part may have dried-out or changed value. Please let us know your results.
Regards,
Craig Baker
706-485-8792
cmbakerelectronics@gmail.com
C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024 |
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Ken Fox
From:
Nashville GA USA
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Posted 21 Jun 2013 8:59 am
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A lot of time old plate load resistors on the preamp tubes will cause a "snap, crackle and pop" noise at low levels. Also a tube can cause issues as well.
Unless you are versed in amp repair that can be a tough one to isolate and repair.
V1 (first preamp tube located to the extreme right) is the bass channel. Remove it, if trouble goes away it is in that channel.
V3 is the normal channel. Remove it as above to check for noise location
V2 sums the signals from Normal and Bass channels (V1 and V3). If neither of the first test work and this tube removes the noise then you have isolated it to things around that amp section.
V4 takes the output of V2 to drive the power tubes. Remove as above to again isolate the possible amp area the noise is coming from. |
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Tommy Boswell
From:
Virginia, USA
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Posted 21 Jun 2013 12:15 pm
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| Thanks Ken! This one's actually been through your shop years ago, according to the forum member I bought it from. It's a great amp, thanks for your help. |
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Tommy Boswell
From:
Virginia, USA
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Posted 16 Oct 2013 7:07 am did some trouble-shooting
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Finally got around to some trouble-shooting, a new preamp tube in V1 fixed the noise problem.
Cleaning the pots with Deoxit did not help the bass channel, so now I guess I need a new volume pot. My schematic shows it as "volume 014038 999K HD". Can anyone tell me how hard that is to find? And to replace myself? My soldering experience is pretty much limited to speaker jacks and cables. |
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Rich Hlaves
From:
Wildomar, California, USA
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Posted 21 Oct 2013 2:18 pm
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That volume pot should be a 1 meg audio taper just as in all the other BF & SF amps.
I don't have a cross reference for the part number but I'm pretty sure.
You can check the value of the pot by measuring the resistance between the two outer legs to confirm.
_________________
On man....let the smoke out of another one. |
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