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Topic: Help with a ShoBud Dual Channel |
Dave Zirbel
From:
Sebastopol, CA USA
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Posted 1 Jun 2015 7:49 pm |
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Hi folks! I have the schematic and hope to eventually take it to a qualified tech but in the meantime hoping someone has some input.
The first channel started making crunching sounds and eventually I got no signal from the guitar, but channel two still seemed to work fine. I let the amp sit for a few months and then replaced the input jack on channel one hoping to fix the problem. Plugged it in and it worked great.....for about 15 minutes and did the exact same thing described above. When I turn the Channel 1 volume up I still get white noise, when I turn it to zero and use channel two it's fine.
There's not too many good techs in my area, and most of them work on tubes. I took it too one guy I know and he really struggled with it.......
Any ideas where the problem might be? I'm thinking in the preamp section. I'd like to get this thing running. My Fender steel guitars sound great through it.
Thanks for looking.
Dave
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Eric Dahlhoff
From:
Point Arena, California
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Posted 2 Jun 2015 8:03 am intermittant noise
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First easy thing I would try is re-solder all the components in ch 1. Every connection.
Next easy thing is to get a can of the "freezer" stuff (Radio Shack?) and one by one, spray each component when it's making the noise.
I have found many an intermittent problem with these 2 techniques.
Good luck!
_________________
"To live outside the law you must be honest." (Bob Dylan) |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 2 Jun 2015 8:23 am
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Thanks Eric. I'll try that. I know solid state amps don't get hot like tubes but maybe something is heating up enough and causing something to expand enough to compromise a connection. I bet if I turn it on today it will work for a few minutes.....
dz
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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John Billings
From:
Ohio, USA
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Posted 2 Jun 2015 10:54 am
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"I bet if I turn it on today it will work for a few minutes..."
Sounds like my ex-wife!
_________________
Dr. Z Surgical Steel amp, amazing!
"74 Bud S-10 3&6
'73 Bud S-10 3&5(under construction)
'63 Fingertip S-10, at James awaiting 6 knees
'57 Strat, LP Blue
'91 Tele with 60's Maple neck
Dozen more guitars!
Dozens of amps, but SF Quad reverb, Rick Johnson cabs. JBL 15, '64 Vibroverb for at home.
'52 and '56 Pro Amps |
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Richard Sinkler
From:
aka: Rusty Strings -- Missoula, Montana
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Posted 2 Jun 2015 4:15 pm
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| John Billings wrote: |
"I bet if I turn it on today it will work for a few minutes..."
Sounds like my ex-wife! |
_________________
Carter D10 8p/8k, Dekley S10 3p/4k C6 setup,Regal RD40 Dobro, Recording King Professional Dobro, NV400, NV112,Ibanez Gio guitar, Epiphone SG Special (open D slide guitar) . Playing for 54 years and still counting. |
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Craig Baker
From:
Eatonton, Georgia, USA - R.I.P.
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Posted 2 Jun 2015 5:18 pm
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Dave,
It's purely a guessing game without really trouble-shooting and signal-tracing, but it might well be a coupling cap that is drying out. Please let us know what you find.
Best regards,
Craig Baker
706-485-8792
cmbakerelectronics@gmail.com
C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024
_________________
"Make America Great Again". . . The Only Country With Dream After Its Name. |
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John Billings
From:
Ohio, USA
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Posted 2 Jun 2015 5:22 pm
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Craig,
If you feed a cap the opposite voltage, can't it act like a fuse? That's what seemed to happen with a pedal when I used the wrong wall wart. It was an easy fix??????
_________________
Dr. Z Surgical Steel amp, amazing!
"74 Bud S-10 3&6
'73 Bud S-10 3&5(under construction)
'63 Fingertip S-10, at James awaiting 6 knees
'57 Strat, LP Blue
'91 Tele with 60's Maple neck
Dozen more guitars!
Dozens of amps, but SF Quad reverb, Rick Johnson cabs. JBL 15, '64 Vibroverb for at home.
'52 and '56 Pro Amps |
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John Billings
From:
Ohio, USA
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Posted 2 Jun 2015 5:22 pm
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Craig,
If you feed a cap the opposite voltage, can't it act like a fuse? That's what seemed to happen with a pedal when I used the wrong wall wart. It was an easy fix??????
_________________
Dr. Z Surgical Steel amp, amazing!
"74 Bud S-10 3&6
'73 Bud S-10 3&5(under construction)
'63 Fingertip S-10, at James awaiting 6 knees
'57 Strat, LP Blue
'91 Tele with 60's Maple neck
Dozen more guitars!
Dozens of amps, but SF Quad reverb, Rick Johnson cabs. JBL 15, '64 Vibroverb for at home.
'52 and '56 Pro Amps |
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Craig Baker
From:
Eatonton, Georgia, USA - R.I.P.
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Posted 2 Jun 2015 6:23 pm
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John,
Good question. Yes, electrolytic caps are indeed polarity sensitive and can be damaged quickly if reverse voltage is applied. If enough current is available from the power supply, it can short diodes and blow fuses. Audio coupling caps may or may not be polarized. Either type can become intermittant and cause the problem Dave described.
Craig Baker
706-485-8792
cmbakerelectronics@gmail.com
C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024
_________________
"Make America Great Again". . . The Only Country With Dream After Its Name. |
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Justin Griffith
From:
Taylor, Texas, USA
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Posted 3 Jun 2015 6:20 am
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Dave,
Please listen to Mr. Baker. He forgot more than I will ever know.
That said, I've worked on a few of these amps, including my own.
Try unplugging the cable that runs between preamp (square box where controls are) and the power amp. Usually that will have a connector with pins and a tube socket they plug into on the side of the power amp chassis. (Do it with amp off please)
If it runs quiet that way, pull out the preamp and replace every electrolytic cap on the preamp board.
Make sure the input jacks are shorting correctly. The channel you are not using has to be turned all the way down when not in use or it'll crackle, buzz, etc, especially if the input jacks aren't shorting when no cable is plugged in.
There are some other caps that probably need replacing in the power amp too. The big blue Mallory caps usually are ok, but there are some others that ought to be changed. They still make those big can caps if you decide to replace them.
Make sure you short the big blue caps before working in power amp. Pay close attention to polarity of caps. They will sure let you know if they are in backwards.
If it hasn't been done already, get a 3 prong power cable on there and clip the "death cap" off the power switch. Mine used to knock the hell out of me until I did. It also got a lot quieter.
Shot me a pm or email if I can help. These are nice sounding amps and can be made reliable.
Good luck!
Justin
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Emmons/Sho~Bud/Blanton, Fender/Peavey.
Telonics pedal |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 3 Jun 2015 7:24 am
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Thanks guys. This is good stuff. I won't be doing the work myself but can do a little troubleshooting and give this advise to my tech. thanks
Dave
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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