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Gadget your probably wondering why I bothered after seeing the 'before' picture..... up close you would see it looked flakey. One observation, this is the first time I ever encountered old style turret boards... they are much more robust than I imagined! .

I didn't have a terminal strip to add the new bias diode like I saw in other photos online. So I got a little creative. Workmanship is important to me, esp. for something as classic as a mac ....... I was hoping someone could tell me if my method of mounting the diode looks ok?

If the info on the webpage page is anything like Tom's clear and instructional replies on the forum, then it will surely be a great resource. Thanks for the link!

This is sad to hear. With the issue with the last pair, the dealer shouldn't have missed this. He dropped the ball and I think you should return them for full refund and take your business elsewhere.

Hey Im sorry to rehash this but just wanted to say I have gotten 12 hours or so of playing the amp with 4 new EH tubes without issue and sounding great! Knock on wood, I think it was just the old Sylvania tube. I was wondering though, was it just my usual dumb luck the tube failed upon first...

Return them before someone here suggest you mod the drivers and crossovers!!

I should have added that might be a good idea.... you don't want to give them any excuse not to honor you. However, if they are only 2 weeks old just get your money back and buy a different pair.

If they are going back to dealer anyway,you have nothing to lose but try to remove all hardware from the driver, confirm it sits flush and then retighten. If not, then your recourse comes from dealer and unfortunetly it will be unpleasant. Good luck.

None were short, it was pulled from a working amp. The top is bulged a bit. All the sections measured pretty high but I know there is likely a large tolerance but I don't know what that would be. So that's the sealing material then, not the electrolyte.

Its certainly not in service. Im just curious about the leakage.

Electrolyte is light colored, similar to a leaking alkaline battery? Then this hard black stuff pushing thru the gaps and bulging the top is probably some sort of insulator or adhesive? Is this capacitor ready to fail violently?

I just wanted to check back and say thanks for allowing me to vent here, AK is great for novices! After mustering up the courage to install 4 new tubes, I monitored current and B+/BIAS at each socket for an hour with the amp at idle. Voltages were stable and consistent with the schematics. I...

If those Fishers work, they will sound fantastic on Cornwalls. For under a grand, I think Bob Latino's ST70 with EL34's on Cornwalls is hard to beat. Make sure to recap your crossovers if they are due.

I put in 4 fresh tubes and it seems to be stable, B+ and bias are correct. I freaked out because I have been playing those tubes for sometime without issue. It only occurred after I replaced ps/bias ! To show my ignorance.... If I were to have miswired a can or something on the bias board... I...

So you think the tube was like that to begin with and that's why it red plated? Or do you think the drifting bias was caused by the red plate event (which would mean I have another issue?)

FWIW: The bias voltage continues to fall (or rise since this is - voltage?) The other 3 are spot on as is the voltage at the bias board (-21).... where the bias falls -16, -15, -14 on that same tube and that happens when I swap it to different sockets. So bad tube??? The only thing I can do...

Ive been playing it for about 30 minutes with music and it sounds good thru the test speakers. However, the tube that red plated is biasing a few volts lower than the other 3... even when I swapped positions. Does that mean this is caused by bad tube? ie: -20.5/-21 vdc at the bias board and...

as you suggested I tried swapping two of the tubes and again all voltages are spot on.... even the tube that redplated, now in the other position, also had proper bias. Perhaps coincidental, when the tube redplated, I was taking measurement at the same time of V2 12au7 which also were approx...

After complete recap of power supply and changing bias board components I powered it up with variac with no problem, it was stable for about 10 minutes at 117vac and all voltages appeared correct... I was getting approx. 390vdc B+ at pin 3 of the power tubes and I was getting -20.5 vdc on pin 3...

Thanks Tom, I was thinking along those lines too.... I didn't think the potting tar would leach up a single wire when all surrounding wires in that bundle are clean. As for the tiny bit of potting tar at the chassis hole, that is evidence of overheat, correct?

Im doing some maintence on a MC225.... I noticed the hole in the chassis the power transformer wires pass thru if you look close there is some evidence of a oily substance that oozed a bit onto the wires insulation. I assume that's tar. Its not a whole lot at all at the opening in the chassis...

With the wire detached the jacks and the chassis are NOT isolated. So that extra wire is a ground loop then, correct? With no hum/noise present, I am paranoid now to remove it... surely the tech felt necessary to add the extra wire, to stop noise or something?

I don't recall a plastic washer but will look closer next time. Again, if its grounded at the jack, is the additional wire a ground loop? ps- Im not chasing a hum problem or anything, im going to replace those doubler cans soon and Im just trying to decide what to do with that wire.

So do you think I should move it to the ground tab that has the ground wires from the pots? If it has a mechanical bond with the chassis at the jack, isn't having the additional wire a ground loop? There is only the one wire, the ground between the two jacks is daisy chained. The removal of...

I'll take a closer look, maybe the mechanical ground with the jack is flakey. If I move it to the tab closest to the jack (I think the pots are grounded to that tab) I wouldn't be creating a ground loop by doing so? The other option is "if it aint broke don't fix it".