sorenb

As I understand, the channel has been working all along, just thrown off by the bal servo. Wonder what the benefit of troubleshooting with the LF353 installed are?

Look at the Uberamp output stage.

.... are D19/D20 the correct value and both oriented correctly (not flipped)? There are some good advice to be found in the posts from @simmconn, make sure you have read those.

Did you test Q24 (J79 in R+ ) ?

To me it seems R+ is not working correctly as it seems to be stucked at ~0V ...does it swing toward B+ at power off? have you tried pull the LF353? does the EL34 heater glow? maybe swap the EL34's in that channel?

Provided the readings are right, I'd look at the right channel LF353 and re-check all the diodes in the right channel servo are properly oriented if everything seems right, pull the right channel LF353 and see what readings you get.

Kevin, wish you a UM66T08

"you should get ~2mA" probably a typo, ~1mA is what I usually get, depending on the DN2540 ...0.5mA might be just fine

I've seen similar. DN2540 leaking usually shows up as the output voltage of the PSU drifting. As far as I remember the supplies breaking down was all wired as negative rails. However, I have not seen it on any GRHV using the cpc1117.

did the SiC survive (someone else’s board with a TO220 DN2540)?

Kerry most likely points to the zeners dynamic impedance which varies with current 1.3mA might operate the zeners too close to the knee

did you check the zener string is actually seeing ground? and the 3k is actually 3k value, and sees source and gate?

did you test whether the css is actually working?

@mwl168 is right 40V offset doesn't sound right. The static may origin from leaking resistors or bad solder joints. Check the 175k's (r10+r11) , r14+r29 and r7+r30 , as well as their joints

Check the current source at the front end should source more than ~1.3mA or so look here for more

+ some human = Hopper

most likely you are measuring at BIAS output, having an output impedance of 5Meg ... and the DMM most likely 10Meg, so the +380V is actually 570V Use the test point (TP) rather to get the right voltage

Indeed a remarkable piece, and always good for a listen ... reminds me of Pears/Britten Winterreise ... and the recent announcement from the Britten-Pears and Snape Malting foundations announcement of an "exciting and logical development": to merge and forget all about Peter Pears ... wonder if the next "logical" step will be announcing that Pears lured Britten into living with him against his will, and the foundation begins to twitt #metoo on behalf of Britten ...

BTW there are (at least) two versions of version 1.8 ... One has the CPC wrongly hooked up, but can easily be fixed: pics are of a skinny

Either remove the CPC if you are not gonna use it, or apply +2V across As said, if you have +18V with cpc1117 shorting, the cascoded CSS most likely needs to be reduced, 4k7 usually works bad soldering?

did you populate the CPC1117 ...either remove the CPC1117 or applie +2V across the pins If you have ~18V on the output, with the CPC1117 populated you probably have to reduce the cascoded CCS current....are you using 2k8 or 4k7?

...sure it wasn't ZIF10?

Have some from PCBNet, 1.6mm and 3oz. Anyone who wants to build the Transconductance amp and post a few pics here, can have a set or two. Promise to show a few pics of the build here, and I'll cover the shipping as well ?

I do

No 0,5 C°/W per channel will do if you go with stock values