Pot replacement, identify correct pot?

[ofens]

It appears to be a type1 ppimv described as a attenuator.

Yes, I have learned this since starting this thread. Thank you!

 

[ofens]

Just get a dual gang B1M pot and replace it, it will cost less then a cup of coffee and if it is scratchy its best to replace it for peace of mind.

Thanks, looking into this now... should I be getting a certain size?

 

[ofens]

This^^^ I would also consider checking your impedance selector. Rotate it several times to clean the contacts.

Interesting... this is one thing I didn't think of cleaning when I had the amp open. Do you think this could cause the fault described?

 

[ofens]

Regarding Deoxit, thanks for the suggestion of D5, I am also seeing recommmendations to use the F5 version of it instead of D5, can anyone clarify this please?

 

[dtier]

Interesting... this is one thing I didn't think of cleaning when I had the amp open. Do you think this could cause the fault described?

Possible but not common with that style selector. Can only speculate. Can you patch from the effect send to an effect return of another amp? Might help narrow it down.

 

[Gutch220]

Regarding Deoxit, thanks for the suggestion of D5, I am also seeing recommmendations to use the F5 version of it instead of D5, can anyone clarify this please?

you could definitely use the fader cleaner version, that would be fine too. In pots, I use the D100 spray to clean it out, then I'll use the needle-tip dropper to work in the lubricant back & forth.

 

[Dixierocker]

The JCM800 2205 being a PCB board amp, sounds to me like you hav a bad trace on the PCB or Molex connector. Lokk for any 2 watt or 5 watt resistors on the board and see if any of the hav e a lifted trace or heat damage.
Just sayin

 

[will01quinn]

I have a my own home made 2204 that I popped this point mod into when I built the amp. Worked for years but has now developed the exact fault. I’ve had a replacement pot sitting in a drawer for a couple of years but haven’t had motivation to replace it yet. With a new born and a 3 year old it’s still a bit too early to be able to use the amp properly.

I must get around to doing the replacement myself sometime soon, let us know if the pot repayment worked. If doing yourself make sure everything goes back exactly as is, otherwise you can easily accidentally change the phase.

 

[Maarten Aerts]

There can be more than one thing wrong. I have a jcm900, not a 8. But reflowing the soldering of the valve sockets stopped the cutting out. Also had to replace the master potmeter such also made it cut out…

 

[ofens]

Hi guys, update: I have got it working again.
Having opened up the amp and used contact cleaner (the WD40 variant), I found that the pot in question became scratchy in movement. Considering that along with the advice on here, I added a lubricant spray into the pot, having read above about the Deoxit sprays, as well as reading elsewhere about similar.
It has worked without hiccup for several days now...

I am under no illusion that the pot needs replacing, but the main thing is I have got it working so I am functional for now, and I am now confident that the problem is indeed this pot, and not hidden somewhere else.
Thanks for the information and advice! This is my first post in the group, and I have to say it's been a good experience to get a variety of replies and insights.

I am still trrying to track down the correct pot to replace it, and it may now be that I just take it to someone to look at to ensure they can get the right part (likely on their shelf already!) and that it is done properly, and might get some other pots and parts replaced too while it's in.

 

[dtier]

The dual 1meg audio taper pot with 3/8 shaft is readily available but if it works good now (as mentioned) don't bother just yet.

I still am suspicious that there is or was something else going on. Again the dual pot controls two signals, both halves of the output to the power tubes. They would have to both fail for the output to drop out but if working don't sweat it. Just enjoy.