s_r

The caps were from the F&T cap group buy here years ago. Definitely going to be keeping a closer eye in the coming years for signs of them starting to bulge again. Like I mentioned earlier it's worrying that they would act this way after only so many years... One would expect caps to last at least a few decades of normal usage. I probably replaced more of the sand than necessary, but the 24V zeners should likely be replaced too as ang728 mentioned.

It must've been either the STTH512Ps or the 24V zeners (or both), since I replaced those and now I'm getting -461V at output. Likely replaced more than what was necessary but whatever, peace of mind is worth more than the parts cost. Should be able to zip everything up and have this carbon playing music again tonight.

2N3904 was also replaced. Doing a diode check the 24V zeners & the 1N4007s get the same measurements as the ones on the working +450V supply. Haven't diode-checked all four but two of the STTH512FPs measure the same as on the working supply as well.

Well I've tried replacing the C2M1000170D, 2x 10M90S, and the DN2540 & got similar behavior. Then I swapped out the LT1021, same story. Then I swapped out all of the sand save for the four STTH512FPs (since I apparently don't have any spares of those). Now it slowly climbs to about -200V & hovers there. Unless only swapping out some parts at a time killed the previous replacements, or unless it's just the STTH512FPs, not sure what else could be the cause of the issue.

One of the big F&T 680uF/550V caps in my carbon PSU decided it wanted to pop mid-listen. Was the v1.7 split PSU boards, specifically the one with the LV supply (the cap closer to the LV section was the one that popped). Certainly left a big mess of electrolytic fluid to clean up all over the inside... The other 680uF caps were also starting to bulge, so I replaced all four. It's concerning that all the 680uF caps would start doing that after roughly 9 years, especially when there was a period of about 2 years where the amp simply wasn't turned on at all. Could the amp's heat be accelerating this? Anyway, the cap seems to have taken out some other parts in the -450V supply with it. Getting about -30V at the output and around the same at the drain & source of the DN2540. I can get other measurements later if needed. Anything else it might've taken out besides the 10M90S (Q1/Q7)?

Good news, two more KGSTs now live and play music. PSUs are set to 400V, so there's plenty of ventilation. I did have one channel with some hum, which turned out to be the tubes. Not sure if it was a bad tube or if the legs just needs some cleaning. Either way I swapped in some RCA 6S4As which worked like a charm.

WIP of a new KGST. I've had the stuffed boards sitting in the closet for who knows how long, so I've decided to finally finish building them. Still waiting on toroids and some other parts, but hopefully I can have this thing playing music within the month.

Good news, everything appears to be working normally now. With some help from georgep and joamat I managed to track down what seems to have been the culprit: one dead 2SC3675 in one of the triplets of 2SC3675's. Probably the reason two of the LEDs nearby were dead too. I just need to plug in some stax now and have a listen... All batteries now measure +200V/-539V, and R42 measures 6.55V just as it should.

Figured I may as well add a pic of the other side of the board. A few of the K216s have 500Ω resistors attached to the gate. The 3675's in the batteries all have an hfe of about 64-67 too.

I'm kicking myself right now, somehow I missed soldering one of the legs of that LED 🤦‍♂️ Values are now -554V/+215V for the right-front and -524V/+200V for the right-rear battery. Besides that their behavior is basically the same; front +200V follows the rear by about +15V, and the front trimpots appear to have no effect.

It's been a while but I have a new T2 amp board that turns on now. I couldn't figure out what was wrong with the old PCB for the life of me so I opted to just rebuild the whole damn thing. However the batteries on the right side aren't cooperating. It's been years since I last turned this on so I'm afraid I've forgotten much of the black magic that is this amp. Anyway, I get -539V/+200V for both the left side batteries as expected. The right side has a few LEDs unlit (and two partially lit) and the best I've been able to get the batteries is -520V/+200V for the rear battery, and -557V/+215V for the front. The front trimpots seem to be totally ineffectual and the front +200V side follows the rear battery by about +15V. Anything obvious I should check first?

Just got my boards in today, thanks.

Paid, thanks.

I'll opt for partially assembled boards, thanks.

I'll take partial assembly if it means some peace of mind when it comes to the HV boards, personally.