Philco 50-T702

[David Roper]

1950 Philco 7" sets are notorious for faulty HV oscillator design. They tend to bloom and fade after about twenty minutes. Not only is there no known cure, one dedicated restorer going to the trouble of replicating the oscillator coil resulted in a brand new coil that does exactly the same thing. Don't shoot the messenger.

[Eric H]

Originally Posted by David Roper

1950 Philco 7" sets are notorious for faulty HV oscillator design. They tend to bloom and fade after about twenty minutes.

Yep, I got one recapped and works well, for 15-20 minutes, then the high voltage fades until the pictures too dark to see.

[timmy]

Well like any other vintage tv, recap the whole set including all the hv caps and then start from there because trying to run it with old caps is not a good idea should one decide to short and take out other components and make the job even harder in the long run.

[tom.j.fla]

Hi, There is a way to solve the HV issue in the Philco. You put in a solid state d.c. to d.c. converter. Now it is a bit pricey if buying new but look on the web to find used converters. Check out this site to see how 1 collector did this, http://www.myvintagetv.com/philco_hv.htm .All the best Tom

[tvdude1]

I have a spare one of those modules if you want it for 40.00 they also work great.

[Crist Rigott]

Yeah, I'm going to recap and recarb the HV section first, then the E-caps, then the rest. At least all the HV resistors too. First I have to see if the CRT is good or not.

Thanks for all the comments, I appreciate them.

[decojoe67]

Originally Posted by David Roper

1950 Philco 7" sets are notorious for faulty HV oscillator design. They tend to bloom and fade after about twenty minutes. Not only is there no known cure, one dedicated restorer going to the trouble of replicating the oscillator coil resulted in a brand new coil that does exactly the same thing. Don't shoot the messenger.

I had okayed my repairman to order one of those replacements (many years ago now) which wasn't cheap, and was so disappointed when I got a call that it didn't work. I believe I was able to return it. My Philco was in real nice shape and I hated to part with it, but having a non-working set in the collection doesn't cut it with me. Glad to hear there's been ways worked-out to fix the problem now. Now if I only still had that set!

[rca2000]

I have said for YEARS..the best thing to to NOW..is to hide a small SS HV module somewhere in the cage (or under the chassis). They have some that will run fine at 6V. You just need to rectify and filter that for the module. One with say 5-7KV output should work fine for the HV.

[Crist Rigott]

Some questions on capacitors and what to order.

I have no problem with what to order for electrolytics.

For the "Bumble Bee" and tubular caps I should order the typical axial lead yellow film caps.

Then there are some caps that have the domino look and I think they are mica caps. There are only 5 of these in the TV. They range from 100pf to 10000pf (.01uf). I'm pretty sure some are mica but I think some might be paper caps.

Then there are some that look like little "hot dogs". These are all listed as mmf or pf in the parts list. There are 31 of them. If I need to replace them, what would I use? They range from 2.2pf to 1500pf.













I'm including some pictures of them.
The schematic is listed in reply #14

[timmy]

Verticle and horizontal Micas would not hurt to change but I would wait on those caps until you get the hv up to see if the crt is bright, don't forget you are dealing with a troublesome 7jp4 crt unless tested on a working set to know for sure. And besides those Micas may be fine as you will see how good they are when you get it up and running.

[Eric H]

I wouldn't change anything in the pf range unless there turns out to be a reason to do so.
The Hot Dogs are probably Ceramic, the Dominos Mica. The square caps of .001 or larger may be paper.

Anything pf or mmf is almost certainly Mica or Ceramic and probably in the i.f. strip where it will mess up the alignment if you replace them.

[timmy]

.01 is not a mica, those hot dog shaped and the others that look like a barrel with colors Are ceramic as well in your picks are usually good, do yourself a favor leave those caps alone even if the crt is good . You should recap the power supply first get it running then look for the hv if none then look for caps and or resistors that are related to hv, rectifier tube as well check or replace. If you have the schematic for that set then it will show what the domino looking caps are once you locate then on the set it will show mmf for the Micas .

[timmy]

If a specific set seems to bloom with the loss of hv then I'm sure when they were new they didn't have that problem, maybe because a cap that was not sized right for the hv section back in the day maybe failed after maybe 2 years and then after 50 years for sure it probably won't work so then why not find the problem or design defect and then that would be the end of that. Being both you guys seem to have the same problem and does look like a mistake was made in the design.

[reichsrundfu]

It's interesting that the drop off in High voltage does not seem to be entirely universal. Obviously there is a design flaw but also not every set produced displays the same result. My 50t-702 comes up nice and bright and yes, after 20-30 minutes I have to adjust the brightness. But after adjustment by it always is watchable and there is no discernible bloom. I've run mine between 90 minutes and two hours and never got so dark I'd have to shut it off! Interesting...

George

[wa2ise]

Originally Posted by timmy

If a specific set seems to bloom with the loss of hv ... Being both you guys seem to have the same problem and does look like a mistake was made in the design.

Maybe they didn't want to pay for a patent license to use a better design? Or just idiot managers telling the engineers to stop worrying and ship it?