Tech-Master NIB TV Kit #5516

[Findm-Keepm]

Originally Posted by timmy

Really nice clean job.

Ditto. Chris, great job.

[Electronic M]

Anything in 30% tolerance is fine/normal in most sets. You may have touched the wrong damper pin...One normally has meter killing HV on it.

[old_coot88]

You'd think the kit maker woulda pasted on a hazard warning in big red letters "Do not attempt to measure plate of H.out tube or cathode of damper tube", since there's a very high level spike there.

[Crist Rigott]

I hear ya! My inexperience showed up on that one. The schematic shows to have 350 volts on pin 3 of V13 12AX4 the Damper tube.

Still a bit puzzled as to why that would happen and especially when the schematic says 350 volts.

[Crist Rigott]

I thought I'd try direct video injection. I injected the video signal directly into pin 2 of the 12BY7A amp. The picture got only slightly better, but still way out of focus.

[bandersen]

What voltage do you have on G2?

[Crist Rigott]

Originally Posted by bandersen

What voltage do you have on G2?

Which tube? On the CRT G2 is pin 10 and that has 301 volts as I let the TV play right now.

[Crist Rigott]

Another thought just occurred to me. When I was doing the voltage checks, the tubes were installed. Could the 350 volt marking on the schematic meant with the tubes removed? Though I don't see how you can get some voltages without them being installed. Just thinking out loud.

[old_coot88]

Originally Posted by Crist Rigott

Another thought just occurred to me. When I was doing the voltage checks, the tubes were installed. Could the 350 volt marking on the schematic meant with the tubes removed? Though I don't see how you can get some voltages without them being installed. Just thinking out loud.

Well, if the 12AX4 were removed, you wouldn't have any voltage on pin 3 (cathode) because it would break the DC current pathway for B+ to the rest of the H.sweep circuit. (Besides, with the tube removed, the other tubes won't light because it's a series heater string.)

The 350V is the raw, unfiltered B Boost voltage, and you sure as heck don't want to measure it at the damper cathode (!). If the kit maker actually measured it there, they were using a beefy old analog meter with mechanical movement that smoothed out the high level spike. And they were highly negligent in not posting a hazard warning.

[bandersen]

OK, they sure made that clear! I'm out of ideas except low HV.

[Crist Rigott]

Originally Posted by bandersen

OK, they sure made that clear! I'm out of ideas except low HV.

Appreciate the help and your videos.

[Crist Rigott]

At the suggestion of someone, I wired in a 2 meg pot to take the focus electrode, pin 6 of the CRT, from ground to 300 volts. I did and that didn't help at all. I also checked to be sure I had continuity from the CRT harness to the CRT base when the connector was plugged to the CRT. That checked good.

Maybe a broken focus wire from the base to the bulb?

[dieseljeep]

Originally Posted by Crist Rigott

At the suggestion of someone, I wired in a 2 meg pot to take the focus electrode, pin 6 of the CRT, from ground to 300 volts. I did and that didn't help at all. I also checked to be sure I had continuity from the CRT harness to the CRT base when the connector was plugged to the CRT. That checked good.

Maybe a broken focus wire from the base to the bulb?

I've seen the e'stat tubes focus well without anything connected to pin 6.
Being a newcomer to the hobby, you don't have access to any of the junk us collectors have, such as another, smaller CRT or maybe a magnetic focus unit.
I know, the gun structure is different on a e'stat focus tube but maybe a magnetic focalizer would help.
BTW, that's the focus look like on the 5AXP4 test tube.

[Crist Rigott]

Originally Posted by dieseljeep

I've seen the e'stat tubes focus well without anything connected to pin 6.
Being a newcomer to the hobby, you don't have access to any of the junk us collectors have, such as another, smaller CRT or maybe a magnetic focus unit.
I know, the gun structure is different on a e'stat focus tube but maybe a magnetic focalizer would help.
BTW, that's the focus look like on the 5AXP4 test tube.

The focus on the 5AXP4 is much better.

[Electronic M]

The hourglasing may also be from a large line transformer too near to the CRT...If you got one near the set move it away a few feet if you can.