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Everything posted by s_r

  1. 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.
  2. 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.
  3. 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.
  4. 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?
  5. I'll opt for partially assembled boards, thanks.
  6. I'll take partial assembly if it means some peace of mind when it comes to the HV boards, personally.
  7. Please add me for the following: 4x GRHVxxx2x GRLV79xx2x GRLV78xx2x Main Board2x miniT2 Thanks.
  8. 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.
  9. 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.
  10. 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.
  11. I wish I knew. I've since tried removing the thermal paste from all the sand on the right channel in case it was shorting somewhere. No change though. Next thing I could try is putting .1uF bypass caps on the voltage set resistors in the PSU. If that doesn't do anything my next WAG is the RK50 being responsible somehow. Desoldering the RK50 seems like it'd be a huge headache, and a risk to damaging the solder points (the pins were a snug fit even before soldering them in).
  12. Where did you source the high voltage wire from? Probably won't be starting a circlotron build myself all that soon but it'd be nice to have beforehand.
  13. As I suspected, the sporadic noise hasn't actually gone for good. I've tried reflowing more joints just in case but that didn't do it. If it helps pinpoint things at all I've noticed that the back right EL34 has a tendency to physically ring. Even if the tubes are swapped around, the tube in that position starts to ring. I've tried putting in mullards, which didn't ring, so maybe the mesas are just more susceptible to ring as a result of whatever is going on.
  14. s_r


    The strapmaker is combat straps, based in Montreal. Also made shipping alligator leather a little simpler than if I ordered elsewhere. This pic shows a bit more of the dial texture, though it's still not quite how it looks in person. Gotta love the acrylic domes that these old watches tended to have too.
  15. s_r


    Really can't capture how nice the linen dial looks in photos. The 5740C is a pretty great movement, very accurate & the smoothness of the seconds hand is nice. Got the strap hand made since I wanted grey with round-scale alligator lining.
  16. Well I've reflowed a bunch of joints (probably more than was needed). Since then I haven't had problems with oscillation, excessive offset, etc. The sporadic noise seems to have gone as well, but of course just as I say that it'll come back to spite me. Anyway, thanks for the help. I think I can stop fucking with it and just use it to listen to music.
  17. Shouldn't have opened my mouth apparently, the T2 is acting up. I replaced the four K216s of the right channel with ones from my old board with resistors at their gates, also trying a 5pf bypass cap right now. Neither of these changes seems to have helped though. It's been a complete gamble when I first turn it on as to whether the offset will be fine, -30V or -450V. Sometimes I'd measure around -30V offset, then as I try to use a scope to see if there's oscillation, the offset fixes itself and there's no oscillation. Other times I'd adjust the batteries, which fixes the offset, then as I'd turn the amp off to put back the top cover it'd regain its problems when turned back on. Regardless of the offset/oscillation I get an intermittent scratchy noise. Just maddening.
  18. So I've installed a 10pf bypass cap. At first the value for offset was way high (like 400V give or take) but after adjusting the batteries it fell back to within normal values. The T2 has been on for at least 5 hours now, and it hasn't misbehaved in that time. I've had to go back and check after hearing some puffs of noise which turned out to be in the recording itself. At the risk of jinxing it, that seems to have worked.
  19. I was thinking of adding resistors to the gates of the K216s in the battery next. If I recall correctly this helped solve some noise in Inu's T2. I'll also try lowering the value of the bypass cap and seeing what that does.
  20. Well I loaded up the gerbers and took some screencaps of the relevant parts. There's certainly a difference between channels. I've also noticed that R86/R87 are physically higher off the board on the right, if that makes any difference.
  21. Put in the second 2.2pf cap just now, and the oscillation looks nigh identical as before. Guess I'll try changing the bypass cap value next. Edit: This is what the oscillation looks like with the bypass cap set to 20pf.
  22. Just the right channel, and it's come and gone up until now.
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