Twin 135 master vol pot gut shot and ?

[fdesalvo]

Here’s the amp that thought me the lesson about bringing old amps inside before cleaning them outside. Something with more legs than I flew out of the chassis and I can’t find where it went. Anyway I have a load of pics, but I’ll start with this one. The master volume pot that typically breaks on these.

I measured a dead spot along its rotation and decided to open it up to attempt a fix. Seems intentional? Can anyone verify before I spend money on a new pot? Tia!

[g1]

That is a tapped pot. Part of the track is missing, so it's definitely shot.
It seems to me they were discussed a while back and the tapped versions are no longer available.

[fdesalvo]

Blast! Weber has a replacement, but not tapped. Not sure what will become of that cap on the next pot.

[fdesalvo]

The pot is shot. The Weber part isn’t tapped, so not sure what to do with this.

[pdf64]

A master vol control needs a bright cap - really?
The amp may well sound better with it removed. I have a hard time believing that it would be missed.
If the pull switch boost is being retained, just swap in the track from a regular CTS 1M pot.

[fdesalvo]

Outstanding suggestion pdf. Will scrub in. Nurse!

[Tom Phillips]

A comment for your consideration...
That brownish area to the right of the tap in the photo of the pot track looks like a coating to me rather than a broken out piece of the track.
I've never seen a mod like that on such a long section of a master volume pot. I don't know what someone may have had in mind if it does turn out to be a coating. Never-the-less, we do run across many goofy things that some old amps pick up during their life.

[J M Fahey]

To me it looks like a section of carbon paint flaked off the Pertinax strip.
In any case, the pot is shot.
If no tap, then donīt use it
Zillions of MV work perfectly with no tap at all, and doubt the original one was doing any magic.
Itīs a Silverface Twin after all, many decisions were taken which didnīt exactly help it.

[Mick Bailey]

I too would not go to the trouble of trying to locate a tapped pot. Fortunately, CTS has maintained compatibility with pots throughout the years, so it's straightforward to re-track them, install new wipers etc. with parts from new manufacture.

[fdesalvo]

The track transplant worked wonderfully. The original track was disintegrating.

[pdf64]

It'll be something of a judgement call whether an audio or linear taper track provides the preferred control action, as the stock J taper would be about halfway between them. I guess that the track of the lesser used channel's vol control could be shuffled along to the master vol control, if it's a big deal.