Hallicrafters T-506 Late Production Set

[M3-SRT8]

Originally Posted by Electronic M

Another technique if you don't want a big power resistor dumping heat under your chassis is to put multiple Silicon diodes in series. I've read that selenium rectifiers drop around 1V per plate( and are effectively a stack of lower rated selenium PN junctions). Silicon drops .7V per plate.

If you are working on a very power hungry set like the nearly 40 tube CT-100 make sure to use 2.5A diodes or make sure there is at least 2-3 component body's worth of lead separating each diode to allow for heat disapation.

Funny you mentioned it...

I was experimenting with deleting one of the 25 ohm 10 watt dropping resistors because Pin 8 on both the 6X5GT and the 25Z6GT were reading a bit low. My Variac turns out to be a bit over enthusiastic on indicated output.

I took one out, leaving one and the factory 18 ohm 2 watt carbon resistor. After doing some power checks the remaining 25 ohm 10 watt resistor (an old wire wound) opened up and killed the power.

After that, I took it and the 18 watt carbon 2 watt out and subbed a single hollow core green wire wound rated at 40 ohms and 25 watts. Pin 8 readings are spot-on and stable now. And I like having one large ww doing the job.

Neater, too.