New build: Loftin-White 6BM8 SE

[Nirky]

Just finished soldering the last wire. Too tired, will attempt power-up tomorrow.

 

[U130421]

The DC DC high voltage converter emits too much EMF noise . To shield, I use it in a single layer PCB box with the copper inside . Double layer should be better.

 

[petertub]

Interesting powersupply ! The 12 > 390V converter may, in my experience, "pump"
if direct connected to a large cap, a small resistor in series will keep it from "pumping"
Try 10 - 50 ohm if you find it "pumping"
Another issue : you have connected the (-) connector to ground , maybe you should ground
the middle outlet instead.

 

[Nirky]

schematic

 

[U130421]

Grid stopper is necessary for the input to avoided the operating current go up and down while turning the volume.

 

[BJosephs]

Good luck. Fingers crossed the first power up goes well. You may need to play with the triode’s plate or cathode resistor to get the pentode bias right.

Have you seen TubeCad’s article reliability upgrades?

Loftin-White Amplifier

A nice upgrade when yours is up and running might be to implement the simple current limiting transistor version. I actually built his inductor version recently.

What’s up with the 100k resistor at the pentode’s cathode?