Need service info for Philco 50-T701

[captainmoody]

I just got started into the restoration of Kam's old Philco and thought I still had the sam's for it, Guess not!
Can anyone help?

[Kamakiri]

Guess that means I packed it well enough for the journey

[ChuckA]

Expect to have HV problems with that model. Seems the majority of them will loose HV as they warm up. The last one I restored I replaced everything in the HV/oscillator circuits even a new transformer to no avail. I finally put together a small 5KV module that plugged into the 6V6 socket, the HV leads then plug into the 1B3 socket.

Also make sure you replace ALL the resistors in the focus string, even though they might check OK now, after running the set for awhile they will change/fail.


Chuck

[captainmoody]

Yes Tim, That foam packing worked great! Also, Thanks for the tips Chuck! Does anyone out there have a sams for it though?

[Charlie]

I've got a Sams for it... 140-7. Zap me your address and I'll send it out.

[Charlie]

I also see there is one on ebay there in your neighborhood...

http://cgi.aol.ebay.com/ws/eBayISAPI...&category=3638

[Eric H]

Chuck can you give us some more details about building that high voltage module?

I have two of these sets, a 50-701 and a 49?-702.

The 702 has had the original donut transformer replaced with one from some other electrostatic set and it's troublesome, the osc only runs when it feels like it and that's not often.
Makes doing any other troubleshooting impossible.

Eric

[ChuckA]

Eric,

I had planned on building a few of the units to sell, but just didn't get around to it.

The heart of the unit is a HV module made by EMCO, they have modules from 100v to 12,000v, the output voltage is adjusted by changing the input voltage from 0 - 15vdc. The problem is the cost, if you buy them from EMCO they want around $200 each, I finally found a guy on Ebay who sells the 10KV model for $40. In fact he has a listing right now:
http://cgi.ebay.com/ws/eBayISAPI.dll...category=36323

The rest is pretty much straight forward, a full wave voltage doubler to supply dc from the 6V6 filament connection, and a LM317T adjustable regulator used to adjust the output HV.

Here's another picture of the unit. The regulator should have a heatsink, I added one after this picture was taken.

If you are interested in building one I'll draw up the schematic and email you or post it if there's interest.

Chuck

[Eric H]

That's an elegant solution for a bad HV transformer, somewhat more expensive that I had thought but still I would like to try one.

If it's not too much trouble I would like to see the schematic?

7JP4 a little weak, crank it up to the full 10K and viola!

[ChuckA]

7JP4 a little weak, crank it up to the full 10K and viola!

Eric,

It sounds good, but really won't work on electrostatic tubes. As you raise the HV it takes more voltage to deflect the beam. After about 6KV you can't deflect the beam across the tube, picture does get a little brighter but you get a smaller and smaller raster.

Also the way this is designed you won't be able to get the full 10KV, to keep the 6vac current close to the 6V6 filament current the maximum output of the doubler is about 12vdc at 180madc so with the 1.2v drop of the LM317 you can only put about 10vdc into the HV module which limits you to about 6.6KV

I'll email you a jpg of the schematic tomorrow.


Chuck

[captainmoody]

Thanks Charlie for sending the service info!
I got the old Philco going tonight after a lot of work replacing parts and repairing rodent damage.
It works good now, But will need to find a crt if I want to use it with the lights on!

[Charlie]

Congrats! Glad I was able to help!