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X-202-B: mod to extend output tube life?

I`m not sure because of the OP using small frame & non zoomable thumbnail pictures of the under side of chassis, but it looked to me that the original FP style PS filter caps are still in the circuit and somebody just tacked new axial ones across them to "shore" up the drying out & failing originals, which can still cause all manner of popping/sizzling sounds out of an old tube amp as the original filter caps are probably breaking down with the most likely. higher modern mains voltage the amp is being used with.
Barring any other issues with it !

Also, aren`t the original 330 k ohm power tube grid resistors supposed to be reduced to the ~200 k ohm range when using new manufacture 7591 tubes in conjunction with the output tubes original input coupling capacitors value upped as well with new replacements ?

Just some random .02 cents value based, thoughts from an old man who remembers stumbling upon and reading these things on this site over 5 yrs ago !

Carry on
 
can we get a shot of the top side? I was also thinking the cans could be old, but tere are newer resistors so maybe they did get replaced. Being able to see what the cans actually are would probably be a clue. New production cans in the old style do exist and it may be those.
 
Photos above, sorry about the duplicate...

One can is marked as replaced in 2007, so I only zoomed in on the old metal and brown ones.

Dave, good tip re: speaker switch. But I went to a local electronics store anyway, asking for a non-inductive power resistor and got a blank stare. He had these, but we could not ascertain whether they're inductive or not: https://www.digikey.com/en/products/detail/nte-electronics-inc/25w8d2/11651928 I'm probably setting myself up as the butt of many jokes here, but that's where I'm at!

Haven't tuned up those sockets and re-attempted the bias yet. Probably a weekend project.
 
One in the clamp is new, I see the CE Manufacturing sticker. The other one looks old. The twist locks are old but not connected. That one old clamp-in one that appears to be in service might be a bit of a concern. If I don't miss my guess, thats the bias supply filter cap. If that fails the output tubes may get very unhappy very quickly.
 
Pull the metal cans off of the 12AX7 tubes and gently rock each one in their sockets. These are the one's that usually cause the crackles and squeals and such. Popping sounds can be bad resistors as they heat up.
 
Not dead yet. Thanks for the replies.

gadget73: You're probably right about that old-looking cap being the bias supply filter, judging by its proximity to the bias pots. It certainly looks old to me, as the one next to it with the sticker as a replacement date from 2007. Gotta go, huh?

I did some cleaning of the sockets & pins, rocked the 12AX7's, and then reattempted the DC balance check. Didn't do the biasing because here's what I got: Channel A, Pin 3 had a ~2.5 V difference and I could only get it down to 2.3 V with the pot maxed fully CW. I assumed this was not good. As for Channel B, the differential was a moving target, oscillating btween ~185 - 215 mV. Not nearly as big of a difference as Channel A, but I wasn't sure if the oscillation was a grave indicator so I stopped. The reading for Ch A was pretty steady.

Thoughts?
 
I'm a devoted can stuffer so that's what I did in my own unit. The cans with the clamps have their flanges below the deck of the chassis. So, if you cut the flange, stuff the can, and replace it, the cut will not be visable at all. More work than most like but I don't mind the puzzle. Of course, as Larry suggested, Hayseed is probably the most popular way of addressing can cap replacement. More $$$ but that is relative. Finally, undermounting too is a common practice but with the tight underbelly of the X-202-B, space is a premium not to mention radiation issues.
 
That is a beautiful link, thanks Larry and Notdigital. Steep price, yes, but I think it will be worth it with my experience level.

And Bill, your observation about the new axial caps shoring up the old PS filter caps appears to be on target.
 
"Also, aren`t the original 330 k ohm power tube grid resistors supposed to be reduced to the ~200 k ohm range when using new manufacture 7591 tubes in conjunction with the output tubes original input coupling capacitors value upped as well with new replacements ?"

This comment from Bill has piqued my interest. What's the deal with new production 7591s and the change in grid resistor value?
 
This might be tied to my last question, but I'm searching also for the schematic for the revered EFB mod for this amp. I've seen the original paper on the Tronola site re: a Dynaco amp, but I reckon the X202B will require different values than what that schematic is showing? And it seems to me that the X202B wll take two EFB's instead of just one. I've searched and found much mention and pics of it in all manner of amps, but no hard specifics besides this Dynaco piece. Apologies if I'm missing something obvious, cuz there are a lotta hits.

If the EFB is proprietary and needs to be purchased, I'm all-ears to this as well!
 
After recapping my dead X-202-B, I set bias as per original instructions. Eight tenths volt D.C. per pair.
What are the negatives going this route other than the adjustment being per pair rather than per tube?
The recap has the entire amp running infinitely cooler, most noticably the power tranny and the filter caps. Waiting to see how long the 7591A last. They are a bit old and used to start with.
I notice that when a 7591 wears, you lose soundstage, presence, and low end. No need for a tube tester.
 
If the tubes aren't matched pairs, you may get some hum and additional distortion. A well matched pair per channel will work just fine though.
 
Had anyone else used this Hayseed Hamfest X202B kit? I'm trying to put in the dual 1000 MFD can cap (C53 on Fisher schem) and it's too big for the orig hole in the chassis.
 
They had to do same for me. Why they do not simply change production to what is actually needed is beyond logic.
 
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