ebay 4-125 new on box $25 shipped. https://www.ebay.com/itm/Vintage-RCA-Radiotron-Electron-Tube-Model-4-125A-4D21-in-Original-Box/362859756845?epid=1927345072&hash=item547c207d2d:g:9XkAAOSw~tJd~9mH
Yes, I meant the rectifiers and regulators... the 4-125 is the reading lamp. The dean of the recording school and I built a PP 845 power amp for cutting records that used 0D3s for regulation in the EQ stage that were a gorgeous blueish purple. He was the first person to hire me in NYC when I was 1/2 way through the course to help him fix all of the broken stuff. The other students were pretty bad with gear and he couldn’t keep up with the workload. We used to get martinis after work and he didn’t know until years later that I wasn’t legal martini age at the time... we stayed close friends for decades afterwards.
Two 866jr rectifier tubes that some are shaped like a light bulb would provide all the lighting magic as the entire globe light up blue. Four tubes in a bridge can provide 2250 volts output. Full-wave center tap connection are only rated for 1125 volts output 250ma for full wave center tap, .5 amp for a bridge.
Sort of. For what he wants to do, the 4-125 is too big, its plate won't show any color at 150 watts out. And the 4-125 needs about 2000 volts on the plate. A better choice in that family would be a 4-65. Lower plate voltage and more glow. Good luck finding a good one.... 816 rectifiers are not easy to find and would be pushed a bit. A better choice is 866As, they're common and rugged when used properly. NO3M does it right:
Four x 1625 or 807 will make plenty of light, 200 W from 5 W, and they show up frequently for under $10/each. You should be able to find an old 1950's or 1960's TV transformer cheap and it will be plenty for the HV and heaters(if 4 x 807). Keep it simple for the first go around. Single band. OD3 tubes or zeners and HV transistor for the screen supply.
Just wrapping my mind around this. Reactance. To counter capacitance wouldn't you add inductance? I probably am not seeing the depth of the "issue" you are presenting, but that is also part of learning and understanding - to figure it out to understand it. That is also a note to add about the "size" - if I have to get creative on circuitry I can have plenty of space.
Ah....no. The current rating for a bridge of four cannot be greater than the current rating of two in a full wave center tap.
