Brought it up again with the variac. With the Selenium Rectifier installed:

At 115 V AC:

6X5GT Pin 8: Spec 390V Test 255V

25Z6GT Pin 8: Spec 260 Test 110V

Is the Sel. Rectifier toast?:smoke:

If you have about 125V on pin 5 of the 25Z6 (V20) the selenium is operating ok.

jr

I installed the diode, with a couple of 25 ohm 10 watt resistors.

Bingo. At household 121 VAC, full Raster came on. Sound on. Pin 8 on 6X5GT reads 390V. Exactly as per spec.

Raster is a bit dull, but I haven't put a signal on nor have I adjusted the 6C4 oscillator.

Should I run it a bit to wake everything up?:smoke:

Good news.
Shows why replace the seleniums with silicon is recommended.
There shouldn't be any problem with running it like this for a little.
Could uncover other problems, don't leave it unattended.

Thanks, No Time Toloose.:smoke:

https://getyarn.io/yarn-clip/6504048...c-95bf796a5a7e

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. :smoke:

Just about ready to load the chassis in the cabinet, but I have two minor problems.

1. Horizontal Position Control, when turned fully clockwise, still leaves about a half inch black bar on the right side of the mask. The Pot tests ok. Is there a resistor I can add to it to increase it's reach?

2. Slight Horizontal Linearity issue. I don't recall any pot to adjust it, and all the high meg 2 watt resistors in the sweep circuits were replaced with much closer tolerances than stock.

Thanks...:smoke:

There's a couple of Horizontal Deflection Load 2 Watt 4.7 Meg resistors. R88 and R90. Sams 91-6.

Should I go up or down on one/both of these resistors to increase reach?

It appears my set doesn't have, or never had, a Horizontal Linearity Adjustment, labeled B2 per Sams, under V17 12SN7GT.

What now, pray tell?:smoke:

Hey...where is everybody?

I thought you guys were smart...:smoke:

THEY Are. I, OTOH.....Ain't...