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s_r

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s_r last won the day on November 30 2023

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  1. s_r

    kgst

    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.
  2. s_r

    kgst

    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.
  3. 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.
  4. 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.
  5. 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.
  6. 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?
  7. I'll opt for partially assembled boards, thanks.
  8. I'll take partial assembly if it means some peace of mind when it comes to the HV boards, personally.
  9. Please add me for the following: 4x GRHVxxx2x GRLV79xx2x GRLV78xx2x Main Board2x miniT2 Thanks.
  10. Been busy listening to this, just replacing the output resistors was enough. I suppose lesson learned is that as soon as you stop looking for rookie mistakes is exactly when they happen.
  11. Don't think I've seen a failure mode like this, but while testing this carbon's amp boards the 5.1k resistors let out the magic smoke. I remember spritzer mentioning that a steel screw should be fine for the crees. Could a short from the screw be possible though? As far as I can tell nothing else blew up. I did spot a stupid mistake which was not soldering the base & emitter legs of the STN9360 nearest to the 2SK170s on one of the boards. I don't think that would cause the same failure in both boards though. Edit: I realized I had the HV supply hooked into the outputs of the board. Talk about stupid mistake. Though I guess that explains why the output resistors were the only components to cook.
  12. It's a good thing I have a decent hakko desoldering gun then. I'll take your word for it, but I'm just worried about taking the pads with it as I lift the RK50 off.
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