Hallicrafters T-506 Late Production Set

[M3-SRT8]

Originally Posted by MadMan

The way I always think about it is the stripe on the diode is the | from the schematic symbol ->|-

Which would also be the opposite of what Tom said, I believe he meant the + comes out of the stripe side. But the stripe side is the cathode (-) and the arrow side is the anode (+). So remember my mnemonic device so you don't get confused: in the symbol ->|- the arrow points in the conventional direction of electricity flow from + to - (not the actual direction in physics, which is backwards O_o [but don't think about that]) and the stripe on the diode is the vertical line |.


https://learn.sparkfun.com/tutorials...d-led-polarity

Thanks for jumping in. Soooo, the TAIL of the arrow attaches to the lead that was attached to the " + " lead of the Selenium Rectifier?

Huh? Oh, Boy.

[old_coot88]

Originally Posted by M3-SRT8

Thanks for jumping in. Soooo, the TAIL of the arrow attaches to the lead that was attached to the " + " lead of the Selenium Rectifier?

NEGATORY. Please see post#4. The banded end (stripe) on the Si diode is the cathode. The "+" marking on the selenium is the cathode, dumb as this seems. The only sensible interpretation is "the B plus voltage comes from here."

[Electronic M]

Originally Posted by M3-SRT8

Thanks for jumping in. Soooo, the TAIL of the arrow attaches to the lead that was attached to the " + " lead of the Selenium Rectifier?

Huh? Oh, Boy.

Nope. Look at a tube rectifier the B+ line comes from the cathode....He is right in that there does need to be a voltage potential across the diode as marked in his drawing to conduct. Think of the old selenium power supply and the load of the TV as 2 batteries in series plus on one connects to minus of the other. They marked the selenium not with it's own polarity but with the polarity of the other battery it connects to.

The stripe on a new diode is the B + end of the selenium.

The old selenium polarity notation is bassackwards from modern convention.

[M3-SRT8]

Oooookay.

I removed the diode and reattached the leads to the rectifier when I attempted to first power it up. Bringing it up on the Variac yielded nothing. No tubes lit.

I checked the switch continuity. It's fine. Checked the leads coming into the switch. They're ok.

Did a resistance check on 6X5GT. Strange readings:

Pin 1: Inf. Test Inf.

Pin 2: 2 ohms Test 1.6

Pin 3: 60k Test soars from 350k

Pin 4: Inf. Test Inf.

Pin 5: 60k Test soars from 460k

Pin 6: Inf. Test Inf.

Pin 7: 0 ohm Test 0.2

Pin 8: 70k Test soars past 1 meg

What's up with this?

Thanks

[M3-SRT8]

25Z6 Readings. Also way off:

Pin 1: 60k Test Inf

Pin 2: 25 ohms Test 144k

Pin 3: 160k Test 1.3 meg and climbing

Pin 4: 64 ohms Test 144k

Pin 5: 10k Test 11.43k

Pin 6: 46 ohms Test Inf

Pin 7 26 ohms Test 144k

Pin 8: 60k Test 1.1 meg and climbing

Weird. And the chassis is recapped, and I've checked everything twice, at least.

[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.

[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.

[M3-SRT8]

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...

[M3-SRT8]

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?

[M3-SRT8]

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?

[M3-SRT8]

Hey...where is everybody?

I thought you guys were smart...

[Sandy G]

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