loudness control no longer available

Hi, I would not attempt to do that as a 250K is 4 times lower than 1 M and you’ll end up reducing the overall impedance of the stage before the pot and the impact will be a greater load/strain on the output of that stage and a greatly reduced overall sound/volume and also the loudness control circuitry (to do with that tap) will no longer act as intended by the manufacturer. I would rather try to fix it and/or keep searching until i find the desired  value pot.  Are you positively sure that the pot is unrecoverable ?  Most of the time in old (era) tube gear the pots are extremely tough to destroy unless the track has burned due to to some leaky capacitors (between stages) but usually if you carefully open the shell of the pot and give it a (repeated and thorough) cleaning with some proper cleaning stuff ! it should (usually) come back to life and work again as new. If I were you I would rather insist in trying to recover it first rather than conveniently looking for a replacement. Sometimes there is a carbon tip that seats between the springy metal  wiper and the carbon track (itself) that wears out and it needs replacing and if you happen to have a collection of old or similar pots (in your junk box at home) you can a similar carbon tip from other old pots that will fit. Sometimes there is no carbon tip on the wiper but rather just some springy tabs that need springing. Sometimes is the rivets of the carbon track (at each end of the pot) that (develop a very high resistance) by getting loose over time and you can tighten those carefully (if you have the know-how). However, in the worst possible situation when the carbon track itself (one track only!) has burned out but the second track is still good there is still a chance that you might be able to find a similar (make and looks single potentiometer) and pinch its track and mount it on yours. So as you can see, there are all sorts of defects that can still be fixed within an old potentiometer before having to finally resort to finding a true and exact replacement. You can also find some tips on how to actually do it on YouTube or some vlogging websites. As an example here is one: https://www.youtube.com/watch?v=AUMxFIH5BN8    and here is another that includes some warning of what stuff to NOT ! use: https://www.youtube.com/watch?v=0ADYRx2jQSE    here is another:  https://www.youtube.com/watch?v=inacV3cUV1A    Good luck.

@ovi4 

 both pots measure 5meg each. fader lube did not help.

@tvmanmarks Is that measuring the end to end track? Check each possible direction and determine specifically where the fault is. Do this with everything disconnected to prevent bad readings. Also verify that the 1 meg spec is accurate, both pots being the same value indicate it likely isn’t a failed part, it is possible that the circuit was revised at some time and may not match a schematic. I have ran into this with the first radio I ever rebuilt, there was 2 versions of the schematic for the same radio with significant changes all around.

@radtekman That’s exactly what I was thinking of when he mentioned that the pots measure 5Megs each. It is kind of ”odd” for both of them to either drift to the exact or very close value and direction and also the jump from 1 to 5Meg is huge!. I am thinking, either have been measured in circuit (which, like you’ve said it can be deceiving) or the schematic had revisions and perhaps the factory might have even issued some ”adendum” to the original build values  like many other well known manufactures did. Another possible scenario could be the amp went from hand to hand and at some point someone has decided that the amp needed new pots but fitted the pots (he had at hand) rather than sticking with the schematic. Who knows…