Filament transformer for 3" Pilot?

[Eric H]

Hey gang, I want to put a 6.3v transformer in my Pilot TV to save the CRT from the start up surge.

I have one already but it's about 2" X 2.25" and is just too big to easily fit inside the cabinet.

Does anyone know of a specific transformer that would be small enough to fit, preferably under the chassis?

It's only going to power the CRT so it doesn't have to have much amperage. Whats a 3KP4 draw anyway, .250 ma?)

[David Roper]

A 3KP4 draws the same 600ma drawn by virtually every other monochrome CRT with a 6.3 volt filament made between ~1938 and 1958.

Display size apparently didn't matter, 1" to 30" and every size in between--600ma.

[cbenham]

A Triad F-13X or a Stancor P-6465, both rated at 6.3V@600mA, both measure
1-3/8 HIGH, 2-3/8 WIDE and 1-3/8 DEEP with 2 inch mounting centers. Smallest I know of, usually found under transformers on eBay.
Best Luck.
Cliff

[Eric H]

Thanks Cliff,

I just picked one up from eBay pretty cheap. Should be able to make it work.

[kbmuri]

http://www.radioshack.com/product/in...ductId=2102700

[Eric H]

Well I hadn't thought of Radio Shack, doesn't say how big it is but it looks small.

The "Tech Specs" say the "Supported Language" of this transformer is English.

[wa2ise]

Just be careful that any stray magnetic field from that transformer doesn't interfere with the CRT's deflection. Interference of this sort will look like a slow waving of the image on the CRT. Turning the transformer physically can help to null this out. Also mounting it as far away as you can helps. Under chassis can help as well.

Back to back 9 V zener diodes could be used instead. 9V as the peak voltage on 6.3VAC is about 9V. Short term overvoltage won't hurt the heater, higher heater voltage is used when the tube is freshly made and evaculated at the factory.

[Eric H]

Got the transformer already!

Under the chassis would just be to hard and would require drilling holes, however it fits nicely next to the i.f. strip and the mounting holes were exactly right to use some existing holes in the chassis so no permanent mods at all.
I stuffed the wires through another pair of holes but haven't hooked them up yet.

This set has been recapped just enough to get some HV and show a line across the screen so the CRT is functional at least but I won't know how good it is till I get a raster.

I've heard too many stories about the 3KP4 popping the heater ( i have a extra 3KP4 with a blown heater) to take any chances, this one does fire up with a bright surge if turned on cold, I only let it do that a couple times before I decided to install a transformer.

[Eric H]

This may have been a waste of time, I've recapped most of the set and have a raster but it's REALLY dim so the 3KP4 is probably shot.

[kbmuri]

3KP4 might still be ok.

Is the new transformer warm? Hot?

The other usual stuff: Ion trap magnet properly positioned? Plenty of HV? Brightness control clean? Drifted resistors in the brightness-control circuit?

If you have a Sams, check voltages at the CRT pins against the voltage chart.

After that, try a tube brightener (or upgrade your experimental transformer).

I'm sure you know all this. Just chiming in for the rest of us.

[kbmuri]

Sams Sheet (62-16) wants 21VAC from chassis ground to CRT pin 1, and 28VAC from chassis ground to pin 11 of your CRT (or a difference of 7 volts). Your transformer isolates the CRT from the chassis ground, so those readings will be gone. But you should measure 7 volts out of your transformer during operation, across pins 1 and 11.

You should have replaced the CRT filament in the AC/DC filament string with an appropriate resistor (someone out there could tell you how many Ohms and Watts). You should be able to measure 7 Volts across it and the 21 and 28 volt readings on either side of it to chassis ground. If not, there's a problem too.

[Eric H]

The transformer measured 8.4 volts without a load, it's a 600ma transformer so it's probably running about right under a load, the heater looks plenty bright enough.

This is an electrostatic tube so there's no Ion trap but I can get a little more brightness out of it by placing a slightly magnetic screwdriver blade near the neck.

There is no sound or video yet either, not even white noise from the speaker,
the HV is unknown but the raster is pretty full and the focus is sharp where I can see it.

Odd enough that it has HV, I know the transformer had broken windings, I just smoothed them down and sprayed Lacquer on them and it worked, they may just be arcing across though because I hear a snap once in a while and the raster jumps.

[kbmuri]

Check for 13VDC at pin 2 of the CRT, and 185VDC at pin 3. These measurements are taken from the plate (pin 5) of your 35W4 rectifier (not chassis ground). The 185VDC is with the brightness control at the mid-range position, and should very either way greatly. The reading at pin 2 might vary also. I've never looked at an electrostatic CRT before so I'm still a freshman. But I would think if these measurements are correct you should have good brightness, if the CRT is good.

There's a 5mFd electrolytic right off of pin 2 as well, looks like it's counting on a 22K resistor to be in spec to keep it charged. I assume you've replaced the cap. Check the resistor.

[Eric H]

I have about 1.5v on pin 2 and 75-150 on pin 3 depending on the brightness setting. The 22k resistor has drifted up to about 33k but I don't think that's going to make much difference.

None of the electrolytics have been changed but they have all been subbed without any change other than the vertical size.

This set has no sound or video, I think I need to concentrate on that area first.
Dim as it is I could probably see a picture on the screen if it was working and the room was dark.

[Gianni]

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