Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fdesalvo on January 25, 2023, 01:15:20 pm

Title: Mesa MKIII Blue Stripe - noisy volume pot
Post by: fdesalvo 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!

Title: Re: Mesa MKIII Blue Stripe - Low Output
Post by: shooter 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:

Title: Re: Mesa MKIII Blue Stripe - Low Output
Post by: fdesalvo 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.

Title: Re: Mesa MKIII Blue Stripe - noisy volume pot
Post by: fdesalvo on January 25, 2023, 03:25:29 pm

Sorted!  TY for entertaining my madness.  Leaking tone stack .1 cap.  Was a dead short!