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Author Topic: No OD - UPDATED  (Read 9546 times)
bobgoblin
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« on: August 22, 2010, 05:22:37 AM »
So, at rehearsal today my 50w OTS just cut out. After troubleshooting tubes, speakers, etc, I switched the OD off at the pedal. To my surprise, I had sound again, just no OD. The PAB still works, but even with the pedal disconnected I cannot manually switch to OD-I get no OD sound at all, just silence. OD off, even with PAB, sound. Anyone care to help me out, suggestions or whatever. Thanks!
« Last Edit: August 23, 2010, 09:14:26 AM by bobgoblin » Logged
boldaslove6789
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« Reply #1 on: August 22, 2010, 05:35:59 AM »
Have you tried replacing the OD tube ? I would try that........
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bobgoblin
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« Reply #2 on: August 22, 2010, 06:08:27 AM »
Yeah, I've replaced v1 & v2 & replaced he PI with a known good tube. Thanks, tho!
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bluesfendermanblues
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« Reply #3 on: August 22, 2010, 08:11:16 AM »
Check the wires to/from the OD relay.
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bobgoblin
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« Reply #4 on: August 22, 2010, 10:03:42 AM »
Thanks!  I'll do that later today.
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bobgoblin
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« Reply #5 on: August 23, 2010, 02:10:30 AM »
Update:

Every tube I've tried produces the same results.  Pin voltages are off, though, so other than touching up some solder joints on V2, I'm at a loss...

Any other suggestions?
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bluesfendermanblues
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« Reply #6 on: August 23, 2010, 05:21:35 AM »
Quote from: bobgoblin on August 23, 2010, 02:10:30 AM
Update:

Every tube I've tried produces the same results.  Pin voltages are off, though, so other than touching up some solder joints on V2, I'm at a loss...

Any other suggestions?

Check the power supply to V2, is it broken of somewhere?
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bobgoblin
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« Reply #7 on: August 23, 2010, 06:51:50 AM »
Thanks, Blues, I appreciate all your help.  I'm new to all this stuff, so tracing connections is very frustrating.  A member of the Amp Garage & TGP known to most D-style players has advised that perhaps the 4.7uf cathode bypass cap has shorted...now to find that & trace the power to V2.

FWIW, Here are my pin voltages on V2:

Pin 1:  185v
Pin 3:  1.645v
Pin 6:  4.29v
Pin 8:  4.28v

Argh!!!
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bobgoblin
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« Reply #8 on: August 23, 2010, 09:21:38 AM »
After chasing the power supply to V2 down, I tested the 150k resistor that feeds the 5uf/180k...measurements are out of range, badly.  So, tomorrow, off to the electronics store for a new resistor & then back to rocking!  (Hopefully...)
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bluesfendermanblues
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« Reply #9 on: August 23, 2010, 09:52:44 AM »
Quote from: bobgoblin on August 23, 2010, 06:51:50 AM
Thanks, Blues, I appreciate all your help.  I'm new to all this stuff, so tracing connections is very frustrating.  A member of the Amp Garage & TGP known to most D-style players has advised that perhaps the 4.7uf cathode bypass cap has shorted...now to find that & trace the power to V2.

FWIW, Here are my pin voltages on V2:

Pin 1:  185v
Pin 3:  1.645v
Pin 6:  4.29v
Pin 8:  4.28v

Argh!!!

 Pin6 & 8 are way out of range....so your problem is V2b
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bluesfendermanblues
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« Reply #10 on: August 23, 2010, 09:53:43 AM »
Quote from: bobgoblin on August 23, 2010, 09:21:38 AM
After chasing the power supply to V2 down, I tested the 150k resistor that feeds the 5uf/180k...measurements are out of range, badly.  So, tomorrow, off to the electronics store for a new resistor & then back to rocking!  (Hopefully...)

5uf/180k Huh?Huh?Huh??

you need 5uf/2.2k
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bobgoblin
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« Reply #11 on: August 23, 2010, 10:48:19 AM »
Yes, sorry, I meant to type the 5uf cap and the 180k resistor that follows it (precedes the 100kL pot).
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bobgoblin
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« Reply #12 on: August 23, 2010, 10:07:29 PM »
Well, I replaced the resistor, but it was a bust, the problem remained.  Nik advised I should remove the snubbers, so off they came & now I'm back in action.  Only question is, is there any harm in running the amp at gig volumes for a while until I receive some new parts in the mail?
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bluesfendermanblues
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« Reply #13 on: August 23, 2010, 10:57:40 PM »
Ok, so the snubbers was the problem ?

You can easily run the amp without snubbers, although it will be pretty harsh in OD mode.
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bobgoblin
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« Reply #14 on: August 23, 2010, 11:32:12 PM »
Thanks, Blues, was just informed 250pf - 270pf is good (RF's values).  I have a 390pf on v2a & a 330pf on v2b for now...we'll see how it works out.

Thanks for all the help!
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