I’m Back! Pilot TV37
 

Hi guys… asking you stand by once again for another all hands on deck. Got the infamous 3” Pilot TV37 on the bench. Of course the first question…anybody got a line on a fresh 3KP4? I think I’ll find some hen’s teeth before I come across one of them!

I did one earlier this year. I need to get a set of the ships wheel knobs, and add the CRT heater protection diode (been variacing it as a protection).

If yours is like mine you'll need to change about %90 of the resistors along with the caps to get good stable operation.

Lucky you. I still want to get a Pilot.

I'm a joyful recapper but 5000pf 6000V caps in the HV circuit? Jeeze...it only makes 2.5K in the HV circuit for the CRT! IDK if I can even find something like that. These are waxies. Can I sub ceramic caps?

You can only use ceramics if you double the capacitance, otherwise you'll have incurable non-linearity in the sweep.

I just go on mouser and get Wima brand red rectangular film caps of that voltage and .0047uF/4700pF they work great in all the various brands of electrostatic sets I've tried them in including my TV-37, and they're the cheapest new cap I know of... Only downside is this leads are short so I have to solder extensions on... Besides that I can't complain. I keep a certain number of them in stock so I can buy and start on an electrostatic deflection set any day I feel like it.

Thanks Tom...I went through DK and didn't find anything appropriate but I did search Mouser and got the exact cap you described...in fact 3 of them. Before I replaced anything, I brought this up very slowly on a Variac and a succession of bulbs. I have static out of the speaker, all the tubes are lit and the CRT filament is lit. No light on the screen though. How do you check the HV on one of these 3KP4 tubes?

Also, I picked up a 1948 Motorola VT71 today. It's in beautiful condition...outside. IDK anything about the CRT or the functionality but I had to grab it. Busy winter coming!

This is a picture of one on eBay...same model as I purchased.

I think I just used my 30KV HV probe and looked for a little on the bottom end.y fluke only does 1KV, and my older meters only do 1600V...

Any of the crt base pins, except for the filament, will show HV? According to the schematic the HV is 2.5K. There’s no traditional donut shaped flyback on the tv. It’s like a large adjustment coil winding

The grid and cathode shouldn't have HV. The deflection plates should. I think I measured HV off the point where the focus divider string under chassis ties in to HV box output.

Got it. Thanks so much

first light!!!!

Good progress.:thmbsp:

Thanks Tom...replaced the HV caps and the electrolytics. Surprised as hell and that picture shows the tube at reduced current...I had a 150 watt bulb in the dim bulb setup. I wanted to go to straight 117 volts and start fiddling with controls but I walked away. I was tired and excited at the same time at 8pm after a long day. That's a bad place to start fiddling with a 75 year old piece of vintage electronics that just woke up after 50 years!

When you have the time, can you fill me in on your CRT protecting diode setup? I've been using the Variac as well.

I can't take credit for the idea, but I do plan to take advantage of the idea next time I place a bulk order at mouser. The idea is basically that an 8.2V TVS diode (think 2 zeners in anti-series) clips AC peaks such that it regulates at 6.3V RMS. Read more here. antiqueradios.com/forums/viewtopic.php?f=3&t=409631&p=3499255&hilit=Pilot+T VS+diode#p3499255

Just ordered 10 1.5KE8.2CA "fuse diodes" from Mouser. Figure I'll be able to find a stock useful.

I plan on doing the same next time I order. In addition to the Pilot I've got at least 7 other electrostatic sets I can think of...Make that 8...So I could definitely use some protection diodes.

So I can use one on the Motorola VT-71 I just obtained and plan to restore?

For any guru out there! I have a raster and I have full horizontal deflection but very little vertical deflection. I'm still a bit shy about running this on a straight 117V out of my Variac so I have it through a 300 watt bulb still. The vertical size adjustment has no effect on the 1 inch high vertical image. I need to do some troubleshooting on the vertical centering pot. I got what felt like a nasty 117V AC shock when I moved it. The pot is just below the AC male socket on the chassis. Don't know what's going on there. I'll need to look at the vertical deflection circuit in the schematic but does anyone have any off the top of the head ideas what might be wrong with this?...other than a lousy pot! I checked all of the pots for ohm values and they all seemed to be ok but maybe I missed something.

Yes you can. Granted on the Motorola if you have a good original ballast (2 of my 3 setsdo IIRC) it's not needed as the ballast should provide a soft start. On a set with a modern replacement ballast the TVS diodes and a thermistor are a good idea.


On my set IIRC the vertical linearity pot was bad. If there are any mica caps in the vertical (or outside of the tuner/IF system) change them. Micas in the sweep circuits tend to be under more stress and die young. If you haven't changed off tolerance resistors in the vertical yet that's definitely something to do. If those suggestions don't help voltage measurements against the schematic may reveal the point of failure.
I did run mine up to 115V on the variac without a bulb once I had it recapped and it was fine...Granted I would ramp it over the course of a minute for safety.

Also I haven't heard of this on Pilots before, but on the Motorola's where the HV is 2-3x that of the Pilot sometimes the octal sweep sockets arc through and create problems that are challenging to diagnose if you didn't expect that possibility.

Thank you Tom. I've changed all of the caps in the set except for the little "pea pod" ones that are all over the place and a couple of HV ceramic caps. I've changed about 20% of the resistors but there are more out of tolerance resistors all over the place. There are a couple of 3kV 300 pf ceramics in and around the HV and vertical circuit that look burned and they'll have to go I guess. I don't see any mica dominos but, that's the only kind of mica capacitor I know how to identify. Are the pea pods micas? I've seen other restoration vids on these sets where these were replaced with modern mica capacitors.

The centering pots are elevated to deflection plate potential (about 2 kV)...is the vertical centering pot missing its insulting “knob” ?

jr

Here are some pictures of the "situation"! The knob does have 2 metal tabs on it that hold it to the sleve that mounts on the pot shaft. Touching that is how I got zapped but I doubt it was a 2kV shock. Felt like your typical 120v AC wall outlet shock.

The 3 pots that are insulated from the chassis are likely elevated to HV...avoid the tabs on the insulated “knobs”.

jr

+1. They're intended to be adjusted through holes in the back with a flat edge screwdriver... I'd use an insulated flat edge driver to adjust them.

I have been since the zap!:bash:

Here's what it looks like at this point. Tom, these little capacitors I described as pea pods, do you know if they're mica?

Could you post a photo of a “pea pod” cap, please?

jr

Yeah. I don't remember anything of that description. A pic might fire some neurons.

Here you go

Ah! the “dogbone” caps are ceramic, and mostly last forever.

jr

Good to know. Just ordered a complete complement of resistors. Will replace every one of them regardless of measured value. I’m going to get a full set of new tubes as well…just to be sure.

Here's an update: What I thought was a vertical deflection issue was not. Somehow, the CRT had been rotated 90 degrees so the vertical was fine...the horizontal was the problem!

Replaced the horizontal amplifier and oscillator tubes but it had little effect. The trimmer cap screws for horizontal size and linearity were seized so I removed the trimmer from the bottom of the chassis, disassembled and cleaned it. When I applied power, this is what I got. Obviously a very long way to go but I have something that resembles a full deflection screen. The Littlefuse diodes came today. Does anyone have any info on how to install one to protect this rare working 3KP4?

Install the diode in parallel with the heater of the 3KP4.

Was it a situation that the 3KP4s were so flaky, and the 3KP1 was the only replacement, or were a lot of these shipped from the factory with 3KP1, because the 3KP4 wasn't in good supply?

Theses never shipped with P1 tubes that I know of. This set is the only application of the 3KP4 AFAIK so there weren't tons of replacements laying around even back then. The TV37 was the cheapest pre-built TV on the market when it was sold and had the smallest screen you could get...Short of portable applications that set probably wasn't desirable enough to put a CRT in once it was 5 years old.

I also have seen first hand a power rectifiers tube in one of these sets fail and pop the CRT heater... I'm just glad it wasn't my set.

Until you mentioned it, I had never heard of the rectifier tube in a TV fail in such a way as to open or otherwise damage the CRT filament, unless it was somehow possible for a defective rectifier tube to put entirely too much voltage on that filament. I would think if the LV rectifier tube were defective in any way, the worst that could possibly happen would be the set's line fuse or the house fuse would blow. The LV supply in these Pilot TVs must have been built much differently from that in most sets of that time.

I don't know what type CRT was used in the Pilot TVs (I've never seen or owned one), but I am thinking the CRTs in those sets is very rare, with replacements almost impossible to find except from a junker. The 3KP4 CRT seems to fit that category. Until I read your post, I personally had never heard of such a CRT being used in commercially-available televisions. Your set must have been made in the days when television was very new, which would have been in the late 1940s.

Why would the CRT heater open if the LV rectifier tube failed? I wouldn't have thought an LV rectifier failure would have anything to do with the filaments in any tube in the TV, unless the failure somehow caused an abnormal increase in heater voltage; even then . . . I just cannot imagine how a failure like this could have caused an increase in CRT heater voltage, or of any other tube in the set.

BTW, it will not be easy to find a replacement for a 3KP4 CRT. This TV was made in the late 1940s, when television was just starting in North America. A new tube will almost certainly be impossible to find. Your best bet would be to try to find a 3KP4 in a junked set, if possible.