Pars

No, the inputs need to be shorted (i.e., pot all the way down). If it like an SS Dynalo, there will be two trimpots controlling offset (one per channel). You want the offset as close to 0V as you can get. <10mV for sure. Nothing to get anal about, 1mV or less is very good. Spritzer might weigh in if he wants to.

I see an Andy Regan listed as president. Might be "Bluto". I think Dan is still CEO, but don't know for sure.

Spotted a solder bridge on 2 pins of the TO-71 socket. It was definitely shorted, now removed. I'll try to test it later. If that is it, that was easy

You measure DC offset at the outputs (signal to ground) with the volume pot turned all the way down. DC V or mV on your meter. Ideally you would disable the DC servos when doing this, but I doubt this is possible on this amp.

Posting some board pics, hopefully of good enough quality. #1 is the bad board, #2 is the good one.

Boy, the hf peeps are sure waxxing on and on about that Viva amp in the CJ meet thread (or amps, the stat one too). Hadn't heard of them (or remembered), but then ran across a thread here with Kevin and Birgir dissing it for the usual types or reasons (ala Rudistor or Mikhail). Nice Alps pot. All of this for $17K? SIgn me up!

I started troubleshooting this today (I'm working, so limited time). After disconnecting from heatsink/wiring, I decided to rerun Soren's CCS test using a bench supply. Both CCS's adjust fine on the bench, so I guess that tells me the 10M90s and DN2540 are fine? I guess the SIC and the PZTA42 are next up. I'll look the board over for solder joints, etc, and run diode tests on those devices. I do have some SICs and I should have extra PZTAs. I did have the opamp and the opto in on this board (no jumpers in). Hope this didn't destroy either of those. I don't think these (if dead) could be causing this issue, but will remove them for the time being.

Yeah, ASR pimps topping hard. I think Amir has a relationship with them. I won't bother reading... I wonder if he measured it correctly given past estat amp history?

Update: fired up the other channel and it works fine. Bias was right where I set it at 17mA. Offset and balance look good. Initial offset was around 32V, adjusted easily down to 0. Let it run a few minutes, it had drifted around 10V, adjusted back down (no servos yet). The heatsink (Modu 2U 300mm) was starting to get warm on that side. The one on the bad channel not getting warm. I did attempt to adjust the bias on the bad channel right side, but the pot had no effect, so guessing a bad device somewhere. I'll probably start with the DN2540 as I have a couple of those. I do not have any more 10M90s. I of course have some C2M1000170D but they are back in stock at Mouser now, and probably not one of those which is bad. I'll attempt to use the good channel to troubleshoot the bad one.

Happy Birthday Naaman! Hope you have a great one!

Went down and started working on this again. The offset pot measured 54.5 ohms in circuit. No adjustment I made to this made any difference and stayed pegged on 404Vdc on the O+->GND. The only thing I've noticed is the right side current adjust TPs show 0.11V. The left side is 0.85V, which is the 17mA i had adjusted to using Soren's procedure. Ohming out the larger devices shows no differences. When you say do a diode check on them, you mean use the diode function on the DMM? I also assume to check them both ways (flip the leads)? From the schematic, the DN2540 or 10M90s could be the culprit on that side. I didn't try adjusting the trimpot, but know they were both set to 17mA. I have a couple of DN2540s, but don't think I have any more 10M90s. I'm going to hook the other channel up and see how it behaves. I verified that the tail resistor for the offset is 120R and not 182R.

That is what I did with a 2CP I bought from PartsConnexion. I measured and plotted the response at several points, and sent it to Chris Johnson of PcX. He replaced it, and the replacement is fine.

Oh, those? They are just bog standard round pads, 1.1mm drill. I used a 1.9304 size on them instead of the Auto in Eagle. I used a square pad for pin 1. EDIT: Here's the datasheet as it is helpful tkd cp600as-e.pdf

Thanks Kevin. I'll check it out tomorrow (having a beer, not conducive to HV stuff). On your production schematic (kgsshvcarbonproductionv5.pdf), the offset pot is RV4 and the balance pot is RV2 I take it? I'm pretty sure I have either a 120R or 100R ohm resistor in instead of the 182R. And yes, my cheapie Harbor Freight expendable meter didn't like the HV (read 400V for the bias when testing the PSUs; Fluke disagreed at 580), so decided I needed another good meter.

I used a long pad type in Eagle which was 2.1844mm with a 0.5mm drill hole. I then put a milling slot on it (instead of a hole) which was 3.2mm long x 0.8mm wide. The older TKDs had larger tabs on them than the more recent ones do. This pad works for either. These boards work fine for a 2CP (I'm using one for that now). You could cut part of the board off for that if you wanted.

Fired the first board up after rechecking all connections, and wiring the inputs to ground. I'm getting full voltage (806 Vdc) from O+ to O-. Nothing exploded or seems to be getting hot, though I didn't leave it on very long. Both LEDs are lit evenly on the board. All pots were centered when I built it, and other than the current source pots, which I had adjusted using Soren's method to ~17mA, haven't been touched yet. I know I've seen this problem in the thread somewhere, off to find it.

A couple of questions: For the balance adjustment, should you measure from O+ to O-? Or is this O+ to GND? I'm guessing the former. For the offset adjustment, I'm guessing O+ to GND (and also check O- to GND)? Also, how critical is it to GND out the I+ and I- (I don't have a pot wired in yet, but could jumper these). It isn't clear in Michael's pics where the blue wire is running to. I bought a 2nd meter (Brymen BM867) so could look at both the +/- offset at once. Thanks!

Links in the first post work for me...

Happy Birthday Dan!

Given that these are so far away from what you view as good sound, I don't think an overly warm tube amp will even revive these. With the price of these, I would return them while you still can. The measurements look pretty bad, even though I don't give ASR much credence.

Wire gauge: I'm wiring up the PSUs to the Carbon boards, but wanted to get an opinion on AWG to use. I had bought a bunch of 22ga teflon jacketed 600V wire from ebay seller skip malley. Since I don't think the HV supplies are sourcing much current, I think this should be fine but want to get any input if you think it is too light of gauge? Usually I've used 18 or 20 for other amps. Thanks.

Happy Birthday Al! I hope you have a great one!

Happy Birthday Colin!

I would check octopart.com and see if you can find any of the semis from a distributor. For the DN2540N3s the other part would be fine if it is the TO92 package you need, not TO220. For the MJW21194, I would look for the 21196 as well (higher rated). If you are in the US, I would use Antek transformers. Something like this: https://www.antekinc.com/as-1230-100va-30v-transformer/ Dual primaries, shielded. These work very well. They also have 28V or 24V if you want to drop that a bit. If you are in Europe, not sure what shipping would look like for these. Otherwise there are probably better options in Europe than buying transformers from Mouser.

Yes, I realized that when I looked at diya. Your screenshot was from there. I know they do have US stock on some stuff; wish they showed that more clearly.