Philco 50-T702 7 Inch TV - Page 2 - Videokarma.org TV - Video

reichsrundfu · #16 03-06-2016, 09:35 AM

Well guys I think I'm there. I found that the root of the vertical linearity issue was a mic capacitor (C73) which couple the first and second sections of the 7F7 vertical amplifier. After the set would warm up, and even with the new resistors there was still some flattening at the top, so when i freeze sprayed that cap the picture came right back up. This is a 100pF capacitor. Soldering in a replacement did the trick. All and all, Im really pleased with the linearity. After getting the chassis back into the cabinet I'll make final adjustments of the height and width, i typically set it 10% oversweep to compensate for voltage variations.

The image is actually a lot sharper than you see in my picture, but I had to set the picture like this to get a good shot of the test pattern. Its quite nice to watch, actually...... After around an hour I do notice the picture gets a bit darker which is typical of this set, but I have plenty of adjustment room on the brightness so i can just tweak it up a bit and I'm fine.

-George-

Electronic M · #17 03-06-2016, 12:54 PM

You might want to check ham-fests for a line isolation type Voltage Regulating Transformer (2 of my 3 came from one day at a ham-fest). I run my regular use sets on them. Those transformers put out a constant 117V or 120V (depends on vintage) line voltage as long as the input is somewhere between 80-160V. They are great at squelching line transients too...Ever had a fridge of the central air system kick on and cause a TV to 'bloom'?...A VRT will end that problem. Some neighbor sharing our pole transformer runs something that, when on, causes that blooming effect several times a minute so a VRT is essential here.

EdKozk2 · #18 03-06-2016, 03:19 PM

Good to see you tracked down the vertical linearity issue.
The picture is much better.

Ed

reichsrundfu · #19 03-06-2016, 06:43 PM

Yeah another reminder to keep your mind open to suspecting mica caps when doing our work. They do fail in increasing numbers now. Remember when you virtually never saw one fail???
George

reichsrundfu · #20 03-28-2016, 04:47 PM

Update for your guys: all done and all buttoned up. I encountered a slightly "rare" issue with the vertical sweep which delayed finishing this. The brand new 100pF capacitor I installed which corrected the linearity problem suddenly began to fail! After about 10 minutes the vertical height would begin jiggling erratically downward off and on. Replacing it with another new capacitor corrected the issue and after a good 8 hours of play time I think she's reliable and ready to close up. Here is what it looks like now!

-George-

timmy · #21 03-28-2016, 04:53 PM

Change all the Micas in the verticle and horizontal sections. These 7jp4 crts if bumped the deflection places can bend.

timmy · #22 03-28-2016, 05:32 PM

Quote:

Originally Posted by reichsrundfu

Yeah another reminder to keep your mind open to suspecting mica caps when doing our work. They do fail in increasing numbers now. Remember when you virtually never saw one fail???
George

Yup they do fail and they all failed in all of my 7 inch electrostatic sets. Mega decades old Micas do fail, age and maybe other components like caps or resistors being out of tolorence helped those Micas fail so next time there is a verticle or horizontal problem and can't seem to find out why even if a slight problem, suspect those little devils. Each set of mine had small verticle problems that could not be adjusted out nor could I find what was going on and I was even told don't touch the Micas they never go bad. So now any set that has Micas in the horiz and vert circuit are now on the list to be changed with all the others as standard. However you will be told here on videokarma do not change any of these Micas in the IF or RF sections unless you are absolutely sure they are bad and I agree 100% . Sometimes things won't be the same or it may need a complete alignment .

reichsrundfu · #23 03-28-2016, 05:58 PM

Fer sure. I e reached the point whenever I experience issues in the sweep sections I go for the mica caps. I suspect voltage levels have a lot to do with it.

BTW: you may remember me, I am the guy that bought your 1946 FADA (RCA 630 clone) a few years back. I eventually replaced the 10BP4 on it with a NOS I came across but we used that sucker in our master bedroom regularly till last year when I scored a mint DuMont RA103 Chatham (doghouse)!

George

timmy · #24 03-28-2016, 06:15 PM

OH ok yes I remember you are from pa but that set had a 12lp4 and you changed it to the 12kpa without the ion trap. I see you finally got on here since when you had tried you had problems becoming a member because of something to do with your email. Well ok welcome to videokarma.

Crist Rigott · #25 03-28-2016, 07:36 PM

Very nice George.

Crist Rigott · #26 03-28-2016, 08:34 PM

Say George would you do us a favor? Could you post some nice pictures of the knobs from your TV? There might be a little confusion as to what they look like. I've placed an ad in the Classifieds here at VK and there was some discussion as to what are the right knobs. Also I'll have a good picture to post of what I'm actually looking for.

Much appreciated.

reichsrundfu · #27 03-28-2016, 09:12 PM

Quote:

Originally Posted by timmy

OH ok yes I remember you are from pa but that set had a 12lp4 and you changed it to the 12kpa without the ion trap. I see you finally got on here since when you had tried you had problems becoming a member because of something to do with your email. Well ok welcome to videokarma.

Hee hee! Yes. Turns out the fellow I acquired this 50T-702 is the site administrator and he figured out the technical problem and got it fixed so I could join!

And yes, you're right. It was the 12" CRT and not the 10" and I upgraded to 12KP4 which was a HUGE improvement! That was a really very nice set (the 630's are very well engineered and executed), although I think the DuMont's are a touch even better.

-George-

reichsrundfu · #28 03-30-2016, 02:22 PM

Quote:

Originally Posted by Crist Rigott

Say George would you do us a favor? Could you post some nice pictures of the knobs from your TV? There might be a little confusion as to what they look like. I've placed an ad in the Classifieds here at VK and there was some discussion as to what are the right knobs. Also I'll have a good picture to post of what I'm actually looking for.

Much appreciated.

I am actually out in Ohio until late Sunday when we return home to PA. When I get back I'll take some pix of the knobs for this set and post them on this thread. So my apologies and I ask all be be patient!

George

Crist Rigott · #29 03-30-2016, 06:34 PM

Quote:

Originally Posted by reichsrundfu

I am actually out in Ohio until late Sunday when we return home to PA. When I get back I'll take some pix of the knobs for this set and post them on this thread. So my apologies and I ask all be be patient!

George

No apologies required. When you get to it. Much appreciated.

reichsrundfu · #30 04-07-2016, 09:19 AM

Hello All,

Per your request, I have posted pictures of the Philco 50T-702 original knobs on another separate thread here so everyone looking to see them will easily find them!

-GEorge-