JoaMat

Made a control board for filament smps today. Some pictures from my kitchen. Idle voltage – no tube 2A3 300B and EML 20B-V4

I believe R41, FB2, C16 and C17 are connected as red line shows.

Thanks a lot. I've been thinking of a 300K resistor cross the h11d to limit the upper grid voltage.

Schematics auto switching. Not sure it's accurate, but that's what I've done. New Grid Voltage Control boards. One trimmer for offset and the other for balance so, both sides are controlled simultaneously. Two jumpers. For 300B/2A3, EL34 and EML 20B-V4. Works al right, quite easy to use. The -510V is achieved with help from GRHV 110V supply. Here is one with Hammond 2VA trafo on board - 2.75in x 2in. New idea - servo controlled grid voltage. Okey, I've tried servo controlled Megatron (with solid state CCS) before and that failed...

A new daughter board to my Megatron something. It sets the grid potential of the output tubes. A few resistors, one trimmer set offset and the other the balance plus a small 120V GRHV supply completes the whole thing. So, I removed cathode resistor along with its decoupling capacitor. EL34 has Vgk 40 V and 2A3 has Vgk 92 V. The amplifier has solid state CCS (no top tubes). Works? so far so good.

From a post somewhere else. I also tested HA-3FXX pins, but I like above pins better. Disadvantage is I had to destroy good Neutrik connectors to get the pins out. Made in Sketchup.

If you need 2SC4686a – check this link. German company claiming they have 4000 pieces available. I bought a couple of hundreds 10 years ago and they were genuine.

I bought some DC bricks from LCSC Electronics. Seems to be an all-right supplier. https://www.lcsc.com/product-detail/C2999063.html

Lovely, finally some use for circlotron psu. Most things settled - only finance issue… no prediction.

Thanks. I avoid ebay. Goods tend to be stuck or disappear in Swedish customs. Suggestions about +/-750V?

Yep, I’ve noticed output and filament boards match up to each other. Here is how it looks like on my screen, all output tubes side by side. Size 24 in x 12 in – huge. Question regarding jumbo socket – what socket do you have in mind? This from a French company might fit.?

Have made schematic out of Kevin’s published gerbers of David and Goliath filament. From schematics a PCB layout following the original gerbers is made and the above 3D model is the result. I’m addicted to make my own twist of others work. So, now can the process of shrinking Kevin's board start. Just to be clear, David and Goliath project is insane. I like that.

Nice Omron relay 3D model, don't you think? Zoom in for a good look.

I’m looking for a way to produce 125 VDC low current. One idea is to use a switching voltage regulator, LT8365 maybe … board size 2.0in x .73in (51mm x 18mm)

Thank you, Shawn. Good to know how Megatron XL behaves.