MLA

I'd say that's a high operating point for this amplifier; the math of push-pull output stages is different from single ended and as long as the transition is smooth you can pick much lower operating points. See for example: https://www.valvewizard.co.uk/pp.html Sorry, I should have remembered; Megatron is NOT push-pull. Megatron (XL) has about 22-23mA through the EL34 current sources. I've tried up to ca 30mA but not beyond that.

Yes; gives roughly +/-4V of adjustment range in my build. Can be upped if larger range is needed.

Regarding you last question, I'm using GRHV in that role so I would say it's doable, but in addition to adjusting the current limiting resistor you need to put some protective measures in place; otherwise there is a good chance the SicFet will blow up during startup (I killed 4 before understanding the problem ). See SimmConn's post for great advice:

I can report that JoaMat's new mini T2 boards are working as designed/intended (apologies for the very untidy photo setup): This is with EH 300b and Amperex 6DJ8 and same filament regulators as JoaMat has shown before. Have only listened to it in mono (which sounded great) since I managed to blow channel nr 2 by re-using a 1N100D that I thought was fine but which wasn't. Lots more current through one of the lt1021's than designed for and it blew after a couple of minutes. Spare parts are on order so expecting to get back to a stereo setup by the end of the week. If you intend to build this, get yourself some 1N100D now. The only place I found with some in stock before next year is TME and it's dwindling fast (was 115 this morning, is 83 this moment).

^ What he said. Live transistor tab and risk of considerable voltage on heat sink, so for testing only and to be treated as an open lid amplifier. The original question for this testing was whether Joachim's latest current source can match the EL34 in performance sonically. After quite a few hours of listening, my conclusion would be yes; a Megatron modified with this solid state CCS is a really great amp (just as the regular Megatron is, btw). Designing a pcb for it where the CCSs can be mounted inside the chassi on proper heat sinks would be a great next step. Let's see if we can convince Joachim to take this on... .

These are really nice; drop in replacement for the EL34s in the current source positions. Just plug it into the tube socket and then spend some time comparing tube to solid state CCS sound. Joachim was kind enough to provide four of these for a Megatron we're experimenting with in Gothenburg. The current source itself is really nice and in comparison to the EL34's, might have an edge when it comes to transient reproduction (completely subjective opinion of course).

all good, but output capasitance 60pF vs 11pF Noted that and am wondering for this application; how much does it matter when used as a current source? I don't know enough of the theory to figure that one out. Help... ?

So, the golden rule for Kevin Gilmore boards seems to be to always follow the board. Schematics are sometimes earlier drafts rather than the finished design, which can be confusing. I have build both the 1.8 GRHVs and the .6 Carbon boards which you have with success. If you go for +/-400V rather than 450V, SimmConn has a nice post on how to push the pzta42 back into a more linear region. The BOM excels and links to Mouser carts posted by mwl168 in the first post of this thread both open and download without issues for me. Should be a good place to start.

GRHV does not fail gracefully... most or all of the active parts might need replacing. Sören B posted a good guide for trouble shooting somewhere.

Next step is usually swapping the tubes between boards to see if it's the boards or the tubes. In the process, cleaning the tube pins might be a good idea; if some have oxidized and have poor contact, hum may occur.

Indeed. Damn, I actually thought I had figured something out

Really nice! From picture, it looks like Ecc99s or similar replacing the ksa1156s?

Working on a BH at the moment, and given what you found regarding Cob for 2690; do you think it would be worthwhile to use TTC004b instead, or is the difference too small? I guess you may have checked it but discarded it as an option?

Very good suggestion; pentaconn is a good idea but the shorting risk sucks.

Not my field of expertise, but I would i imagine the start sequence is designed to start from full power, so if it was me I'd rather just flick the switch and see what happens as I would be worried that gradually ramping up voltage might leave parameters out of spec at the wrong time... But that's mostly a guess :).