I Have been making SECA amps now for about 48yrs.
The first one was with Mr Elsdon and myself it was just 12W, then using FET's and Darlingtons in the output stage.
The first one is still working my old friend a retired Doctor has it under his floor board and driving IMF speaker.
The first FET I used was made by IR and by heck did they get a few things wrong, I now use a Si die based on the IXYS designs.
And a precession constant current stage, none are based on Mr.Hoods design or have a massive choke and all are DC coupled with a max of 10mV DC offset.
OK the heatsink as to be big.

read a bit more here. www.abcaudio.biz/amplify
and here seca.freeforums.net/thread/2/seca-kits-wonfor

I also built the largest in the world
Only 300W Mono, 1.5F caps, 2 of 2KVA transformers and at 180Kg and 6ft was more likely to give the thief a hernia than steal it.

That’s big! What was that made for?
The biggest one I made was 100w.
Have you seen Nelson Pass’ designs where he dynamically drives the constant current source?

AMR-iFi R&D

Mar 2, 2021 20:57:40 GMT 12 colinf said:

That’s big! What was that made for?
The biggest one I made was 100w.
Have you seen Nelson Pass’ designs where he dynamically drives the constant current source?

Do you mean like a good A/B design.
None of the Nelson designs are single ended.
The monster I made because Nelson told the world he a built the biggest Single Ended Class A amp at 50W, we now see what he really did he made a Push Pull Class A.
Now being very British I could not allow a Yank to say he made the biggest Class A, so these SECA or TOCA amps were born.
The 300W Mono dissipated 1800W, the heatsink held 80 power MOS FETS and 80 Darlington's as CI. 
The two 2KVA transformers and the 3 banks of caps each bank 1.5F.
The front was made from Granite. This lot weight in at 180Kgs each.
The large caps, well SECA designs have trouble ignoring ripple so the bigger the better at a rough guide 1 V ripple at 1 Amp needs 10,000uF full bridge and 50Hz. or you add a monster voltage regulators but I like the K.I.S.S. topology practices.
We sowed the whole range a RAMADA Hotel near Heathrow.
I very nice Yank sat next to me there not knowing each other we had nice chat it turn out to be Dan Agostino the Krell King, a lovely man. He thought at first the huge things were speakers, but the speaker were ProAC and about 6 inches shorter.
The whole show for the TOCA was paid for by Baron Peter Mates in Germany a good friend and he owns and made most of the paint rollers you use today, he also made medical kit and furniture, I spent time with him in his castle so after my wife Jenny died he and his family help me recover.

Very nice, very hot! Yes Nelson's designs are then technically push pull if the current source is driven.
My big amp was SECA as well, I’ve been making SECA since I was about 11. (Mainly because I was too lazy to add the -pull part and it sounded better anyway. Harmonically more consistent) It used 10 BJTs a channel driven by a jfet-BJT-diode thingy with bootstrapped drain and ccs, also servo loop for DC correction. I made it to drive my Magneplanars.
edit..oh, and parallel distortion cancellation in the pre-driver.

AMR-iFi R&D

I also experimented with IGBT,s only the small 1200V at 300A type sounded ok but top end rolled off.
Then I tied FET,s with a series Schottky in the source and around from the cathode to the drain of the FET another Schottky diode, this technique is in use manly in Full Bridge Resonant SMPSU (50KW +) designs and allows you to reduce the heat in the body diode of the FET thus keeping the RDoN lower at higher temperatures, but the added side effect on the device is you reduce the load capacitance and get better BW. OK you have VF on the conducting diode of as low as 0.2V but it is worth trying. The diode only needs to be a 15V type, and I suspect the new SiC are even better. Now you could add a series FET with a zero crossing detector and thus making a super diode. This I have also tried in bridge rectifier and it has been copied many time now, I first used it on a cruises missile in the early 1990 and had VF of 10mV at 50Amps.And in a six phase power system that mean a much smaller heatsink, more room for the bang stuff.

Here is a cct for the FET bit

seca.freeforums.net/thread/new/1


fet help.pdf (8.49 KB)