Philco 48-2500 Restoration Blog

[TV Engineer]

The problem with these sets is most definitely high voltage sag with increasing beam current...

The sag is the result of the voltage drop across the 1X2s...

I had one of these sets once, and after experiencing the blooming issue to the point of considering the set unwatchable, I removed the 1X2s and their associated filament windings and installed a solid state high voltage tripler (extracted from an old color television chassis) in their place.

The results were stunning.

High voltage regulation was vastly improved, and the focus issue was almost completely gone (only with the brightness cranked all the way up.)

ETA: I also installed a retrace supression circuit in that set so I could crank up the brightness a bit without having retrace lines. It worked flawlessly. BTW, don't remove the DC restorer. It will just make the set more unwatchable.

If you can stand to do this to your set, this is the cure.

[Tom Albrecht]

TV Engineer,

Any tips on where to get a solid state voltage tripler? Do a lot of modern CRT sets have them, or is it something a bit obscure to find?

Tom

[Don Lindsly]

The most frequent high voltage problem comes from bad "Presistors" in the multiplier circuit. They are special high voltage 2 meg resistors. There should be plenty around. I have some if all else fails.

[TV Engineer]

Originally Posted by Tom Albrecht

TV Engineer,

Any tips on where to get a solid state voltage tripler? Do a lot of modern CRT sets have them, or is it something a bit obscure to find?

Tom

Almost any American solid state color set (and a few hybrids) from the early 70s til the early 80s have them. Zenith, Magnavox, Sylvania, RCA, Admiral... they all used them at some point. You can also order one new with the ECG/NTE523 part number. They're about $25. Hook the output of your flyback to the in, ground the ground pin, and connect the output to your CRT. Ignore any remaining pins. That is all there is to it.

Somebody here mentioned the 2 Meg resistors in the original tripler circuit being bad...

They did fail, but if yours were bad, the regulation would be even worse, and you might not have any high voltage at all. I experienced this with my set too. I replaced them, but the HV regulation still sucked, which was when I came up with the solid state tripler idea.

Let us know how it works for you if you try it.

[Eric H]

Success, after a couple false starts.

I took all the tubes with me today and tried firing the chassis up during my lunch hour, all I got was a glowing red plate on the 6BG6.

I messed around with it a little, pulling the cap off and seeing how much current it was drawing, anyway I fooled around a bit too much and cooked the 6BG6, it shorted and caused a little 50v cap on the Damper tube to explode.

fixed the cap and did a little troubleshooting around the Horiz Oscillator tube, I had zero B+, a little troubleshooting found a solder glob that had shorted a 120k resistor (R115 on the Sams) to an adjacent terminal on the strip, cleared that out and the voltages on the Osc tube fell in line.

Now that I knew it was probably working I went and borrowed a 6BG6 from a friend who lives near my work, put it in and fired it up.

The first indication that I had HV was the inch long spark that jumped from one of the doorknob caps to the second anode lead, the lead has a bad spot where I melted it with the heat gun.

Moved the lead, grounded the CRT more securely to the metal bench and tried again, this time I got a raster!

The raster fills the screen, I put in a set of tuner strips and it appears I'm getting something through the i.f strip, if I had a DVD player I think I could get a picture.

I used the CRT that came with the set, it was the most burnt so I figured I had the least to lose if something went wrong.

It works OK, decent brightness after it warms up a little but the area where the phosphors are burned are noticeably dimmer, there's also a barely noticeable vertical line burned in the screen, I think this is due to the way the set warms up, there's a brighter vertical line first then it expands and fills the screen, it could have had a horiz sweep failure at some time too I suppose.

There's also a faint image of Uncle Milty burned in the screen (just kidding but that would be cool)

Next I want to try my supposedly NOS TP400 and see if it actually works.

[mbates14]

[Eric H]

At your command!

Here's a couple shots of it running, this is with the NOS tube.
It doesn't seem to get all that bright, except when you adjust the controls it'll get brighter for a moment then settle back down, I think perhaps it needs a signal to work it's best.

All I know for sure is you have to be really careful where your wires are laying when you turn this thing on, anything that gets in range of the HV area will get zapped! I don't have the cage on it yet though, wonder how much X-rays it makes if any?

BTW, when it's installed and adjusted properly the screen won't be filled like it is now, it's supposed to be a bit smaller than the tube and keystoned slightly to compensate for the angle of projection, this can be seen on the face of the old tubes in the brown Phosphor.

A pair of magnets attached to the sides of the CRT do the keystoning.