Tech-Master NIB TV Kit #5516

[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.

[dieseljeep]

Originally Posted by Crist Rigott

The focus on the 5AXP4 is much better.

Boost the line voltage another 10 volts or so. See what the focus and brightness looks like then. You installed E'caps, that were rated for higher B+ so no worry.
I just looked at an old Sylvania tube manual for the specs on the 21FP4 and it shows the focus voltage, rated between -200 to 1KV on pin 6. I don't remember seeing, that kind of voltage used for E'stat focusing. It was always between ground and boost.

[old_coot88]

Originally Posted by dieseljeep

Boost the line voltage another 10 volts or so.

And if that shows promise, consider sticking a few 9V batteries in series in the B+ line feeding the H.out circuit. That would give it even more grunt, B Boost and HV without overstressing the heater string.

This would at least give a yes/no whether raising B+ further on the H.out circuit would help.

The battery string would go in the B+ line feeding the plate (pin 5) of the 12AX4. If it helps, then consider building a small dedicated supply in place of the batteries.

Just a thought FWIW.

[old_coot88]

P.S. If you're interested in trying the 9V battery trick, I have a ton of them which are pulls from smoke detectors in my building. They are Mallory Duracell and all test well into the green on a standard batt. tester. The pulls are always good since they're changed on one-year interval.
Free for postage. PM me if interested. Bill

[Crist Rigott]

Here is a video of the picture quality. The picture is a lot more focused just after turn on but then looses focus after that. Watch the SUN day of the weather to see what I mean.

https://youtu.be/DXsw8_pofTA

[Crist Rigott]

Originally Posted by old_coot88

P.S. If you're interested in trying the 9V battery trick, I have a ton of them which are pulls from smoke detectors in my building. They are Mallory Duracell and all test well into the green on a standard batt. tester. The pulls are always good since they're changed on one-year interval.
Free for postage. PM me if interested. Bill

Stand by for preliminary tests.

[Crist Rigott]

Originally Posted by old_coot88

And if that shows promise, consider sticking a few 9V batteries in series in the B+ line feeding the H.out circuit. That would give it even more grunt, B Boost and HV without overstressing the heater string.

This would at least give a yes/no whether raising B+ further on the H.out circuit would help.

The battery string would go in the B+ line feeding the plate (pin 5) of the 12AX4. If it helps, then consider building a small dedicated supply in place of the batteries.

Just a thought FWIW.

OK, it's worth a try. What, like 27 to 36 volts?

[Crist Rigott]

Originally Posted by dieseljeep

Boost the line voltage another 10 volts or so. See what the focus and brightness looks like then. You installed E'caps, that were rated for higher B+ so no worry.
I just looked at an old Sylvania tube manual for the specs on the 21FP4 and it shows the focus voltage, rated between -200 to 1KV on pin 6. I don't remember seeing, that kind of voltage used for E'stat focusing. It was always between ground and boost.

I could boost the line voltage by 10 volts. Would that hurt the filament string?

[dieseljeep]

Originally Posted by Crist Rigott

I could boost the line voltage by 10 volts. Would that hurt the filament string?

I forgot to mention using a Variac. Many will put out 140 volts.
You can boost the B+ by using a 12V heater transformer, rated at around an amp, connected boost. Connect it before the rectifier and you'll just increase the B+, without increasing the heater string.

[Crist Rigott]

Originally Posted by dieseljeep

I forgot to mention using a Variac. Many will put out 140 volts.
You can boost the B+ by using a 12V heater transformer, rated at around an amp, connected boost. Connect it before the rectifier and you'll just increase the B+, without increasing the heater string.

OK, I can do that.

[Crist Rigott]

Originally Posted by dieseljeep

I forgot to mention using a Variac. Many will put out 140 volts.
You can boost the B+ by using a 12V heater transformer, rated at around an amp, connected boost. Connect it before the rectifier and you'll just increase the B+, without increasing the heater string.

OK here is what I did. I connected a 20 ohm 25W resistor in series with the heater string. This allowed me to increase the B+ from 124V to 135V. Going from 124V to 135V the picture just got bigger and not any clearer. My variac could only bring the mains up to 132vac.