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Hoffman Amps Forum image Author Topic: Mesa MKIII Blue Stripe - noisy volume pot  (Read 1844 times)

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Offline fdesalvo

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Mesa MKIII Blue Stripe - noisy volume pot
« on: January 25, 2023, 01:15:20 pm »
Hi, all.

Working on a customer's MKIII.  Scratchy volume pot eludes my skills.

- Electrolytics test good
- Voltage at sockets measures good
- Replaced PI coupling caps
- Replaced C505/506
- No DC on pots
- Subbed in new volume pot - no change
- FX jacks clean
- Power and preamp tubes good

Any tips?  TIA!
« Last Edit: January 25, 2023, 02:43:20 pm by fdesalvo »
~F
"Ruining good moments since 1975."

Offline shooter

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Re: Mesa MKIII Blue Stripe - Low Output
« Reply #1 on: January 25, 2023, 02:23:12 pm »
since you have FX and the thread is low output, jack in an audio source with volume and split the amp's "issues" in half
not looking up the schematic cause the snow is just perfect for wandering around in :icon_biggrin:
Went Class C for efficiency

Offline fdesalvo

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Re: Mesa MKIII Blue Stripe - Low Output
« Reply #2 on: January 25, 2023, 02:39:28 pm »
Hey I just revised the post lol. Only remaining issue is noisy volume pot. Turns out I am getting DC on one V1's grid as I wind up the volume.  Looks like I have DC on one side of the tone stack caps.  Hoping this is it and not a leaking LDR.
« Last Edit: January 25, 2023, 03:06:52 pm by fdesalvo »
~F
"Ruining good moments since 1975."

Offline fdesalvo

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Re: Mesa MKIII Blue Stripe - noisy volume pot
« Reply #3 on: January 25, 2023, 03:25:29 pm »
Sorted!  TY for entertaining my madness.  Leaking tone stack .1 cap.  Was a dead short!
~F
"Ruining good moments since 1975."

 


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