Marshall Reverb12 Gain pot Trouble

[BWClara]

Hi all,

I'm posting this thread from Japan.
At first,sorry about bad English.

I just got an old Marshall Reverb12 amp,but Gain pot have a problem.
Turn the pot to till Lv8 sound is clean,and from Lv9 suddenly distorted.
So too difficult get crunch&overdrive sound.

I tried replace the gain pot to new one(22k Linear) and replace OPamp too,but same result.
Then I tried replaced the pot to 22k Logarithm,I can get smooth gain up comparatively.

And now I have questions.
This amp's Gain pot which is original Linear or Logarithm?
If 22k Linear is original,then my amp may have trouble at another parts?

Ex-owner said he just replace Volume pot only,because of scratch noise.
I've searched schematic of this amp.
http://www.drtube.com/schematics/marshall/5205.gif
But there's no notation Lin or Log.

Is there someone own Reverb12 tell me Gain pot's notation?
And are there some advices to repair this amp?

regards.

[Jazz P Bass]

A log pot will give a smoother resistance value sweep.
If it works better, use it.

[BWClara]

Thanks for your reply!

Now I'm using Log pot as you say.
But just want to know original specification.
And afraid about another parts trouble...

[Gunny]

It's not a super high tech amp. Marshall takes short cuts just like the other amp companies. If they can get away with a linear pot where it should be a more expensive (although pennies) audio taper pot, they'll do it. That means you are OK to deviate from the specifications of this amp because you are actually improving the component and circuit quality to a higher spec.

[BWClara]

Hi Gunny,
I satisfied with your reply!

After posted this thread,I researched about Lead12&Reverb12 a lot again.
Then I knew this amp doesn't have wide drive range originally,because of Linear taper pot.

Now I use audio taper pot,it's the best for me.
Anyway,I've come to think this amp is not broken.

I'll treasure this amp!
Thanks a lot!!