I've been working on this Tele-Tone Porthole for the last couple months, finally got it recapped and replaced some out of spec resistors.

It plays pretty well but I'm having one last problem and I'm thinking it could be some bad Micas in the Horiz circuit.

It'll play fine for a while then it starts to tear at the left edge, sometimes it flops over completely or tears so bad it's unwatchable.

This is basically a 621/721 chassis, it has three trimmers on the back of the chassis for Horiz Drive, Frequency and Locking Range.

There are Micas connected to the trimmers so I'm suspecting they could be the problem?

Pic 1 is working normally, pic 2 shows the tearing.

I would certainly suspect the Micas. I'm doing a 1948 Philco 48-1001, and there are 7 Micas, thankfully, only seven, to worry about. I tested them all and they were fine, except one.

However, I haven't fired up the Chassis with CRT yet, as I'm waiting on a Focus Pot, and a few odds and ends. If I get the symptoms your reporting, I'll replace what Micas are suspect.

That's all there's left, as I have completely recapped the entire Set, except the Micas.

I'll know Tuesday. If I were You, I'd shotgun the Micas in the affected circuit.

LJB

Yes, some old micas are showing their age. I replaced a few in my RCA 630TS on the advice of another restorer.

Phil Nelson

A lot of those "micas" aren't really mica caps at all... Especially the reddish-brown ones in the RCA chasses. They're nothing but paper caps in a flat bakelite casing. I usually find the ones on the horizontal oscillator transformer way out of spec, along with the ones coupling the tuner output to the 1st IF, and the IF interstage coupling caps. Replace with true Mica caps, if you can find them.

Charles

Horizontal circuits work their caps a lot harder than RF and IF circuits do. So the horizontal micas (if in fact they are micas) could be bad.

I agree with the posts but for troubleshooting purposes, take a little freeze spray to the suspects one at a time and see what happens.

Those epoxy dipped micas are still available, 500 volt rated.

LJB:smoke:

Can these be replaced with Ceramic Discs? Those I can get locally otherwise I'll have to order them and wait.

At least a couple of them are rated at 1000v by the way.

Can these be replaced with Ceramic Discs? Those I can get locally otherwise I'll have to order them and wait.

At least a couple of them are rated at 1000v by the way.

I don't believe so, but, someone else who's in authority should chime in.

CE Distribution carries those nice Epoxy dipped Silver Micas, in values ranging from 10 to 1000 pF, rated @ 500 watts. Mucho better than the old dominoe micas, I'm sure. I'm using those.

website:

www.cedist.com

LJB:smoke:

Can these be replaced with Ceramic Discs? Those I can get locally otherwise I'll have to order them and wait.

At least a couple of them are rated at 1000v by the way.


I'm not the world's expert, but based on experience and on the knowledge of engineers with whom I've discussed this in the past, the answer is No. The ceramic discs are too temperature-unstable, and you'd be adjusting the horizontal hold every 5 seconds. I know that All Electronics, Inc has micas, but they're here in the LA area. However, for troubleshooting purposes, you could parallel two paper caps, and that would be much better than a disc, and certainly better than leaky/open/shorted original micamolds. (if it's a .05, use two paper .022 @1600v). That way, you could order the micas knowing whether it's going to solve the problem.

Charles

I have been told more than once that ceramic discs are not suitable for horizontal circuits. Something about not being good with high frequencies, although I'm sure that temperature instability wouldn't help, either.

Phil Nelson

I had to order a few replacements for mica caps, got them from Moyers . Silver mica caps i think they were @ 600 v . Worked just fine in the Philco i finished and they were in the horizontal deflection circuit .

There are various ceramics used. NPO, Z5U etc. They all have different characteristics. Z5U changes capacitance with voltage. It also changes with frequency.

I have no experience using them in horizontal circuits, but I agree with the others that they are likely to be problematic.

If you have film capacitors of the proper values they might work though. I don't think the frequency is high enough to be an issue with them.

John

I think I'll just make up a list tonight and order the Micas, there are only a half dozen or so.

They are all in the Pico range, 5-500 Pf I think.

BTW, this seems to be a Phasing problem rather than Frequency, the picture doesn't flop sideways so much but mostly just shifts sideways so the picture's split in the middle.

I think I'll just make up a list tonight and order the Micas, there are only a half dozen or so.

They are all in the Pico range, 5-500 Pf I think.

BTW, this seems to be a Phasing problem rather than Frequency, the picture doesn't flop sideways so much but mostly just shifts sideways so the picture's split in the middle.

Now I'm waffling. In the range of 5-270pf you could get COG disc ceramics that are very stable and have low dissipation. It would be hard to find values above that though in COG. You're probably better off getting the micas, but now I'm curious.

John

In the Philco 48-1001 I'm working on, I just replaced all the "Domino" micas with Epoxy-dipped 500v micas. They all tested fine at rest, but, to quote Remo Gagji in "Casino:"

"...Why take a chance? Anyways...that's how I see it..."

LJB:smoke:

PS: These "Domino" Micas are 60 years old. Plus, they control some pretty picture quality-related circuits. Time for Retirement...

I could get a few discs and see what happens, they're well under a buck each locally.

The set won't sync at all now, it's pretty much stuck with the bar down the center, that might make it a little easier to fix!
It was acting up only now and then which is a major PITA to find.

I'd like to get this thing off the bench (i.e. kitchen table) so I can start on the monster Philco 49-1280 :)

I spent a couple hours on this last night, up till 3:00am actually and went to bed frustrated.

The set worked good after the initial recap but would tear and pull sideways occasionally, the last couple days it crapped out completely and the picture was a jittery mess.

I found a 100pf cap on the sync sep tube that responded to heat, I replaced it with a .001 mylar, it worked and the picture was rock solid but now it was split down the middle with two pictures side by side.

I fiddled for two hours replacing resistors and subbing caps to no avail.

This morning I turned it on again and it works perfectly, go figure.

I still think it has some bad Micas or whatever these square flat caps are, they are Micamolds so who knows but I'm going to replace them (one at a time of course so I don't get myself into more trouble)

Pretty nice picture when it's working! There's a lot of detail in that tree.

John

Word on the street is to never trust a Micamold, it's just a paper cap in disguise.

I let it play for two hours this afternoon, not a hiccup, shut it off and back on, still perfect, on again now several hours later and still fine!

I'm still going to replace the Mica(molds) in the Horiz section though.

My fingers are crossed for you! I know that feeling of knowing there COULD be an issue, but it isn't showing up. When the picture is split and solid, it's usually a Horizontal Phase problem. If that set uses a 6AL5 as the horizontal phase tube, try changing it. Those are ultra-sensitive, and can do that type of thing even if the tube has good emission.

Charles

In my limited experience, it's the rectangular Micamold caps that are paper and should be shotgunned without thinking. Square flat ones are usually real micas, regardless of brand name. But as mentioned, they can go bad, although much less frequently than papers.

I love it when problems cure themselves, though!

Phil Nelson

I let it play for two hours this afternoon, not a hiccup, shut it off and back on, still perfect, on again now several hours later and still fine!

I'm still going to replace the Mica(molds) in the Horiz section though.

Eric, at some point could you post a photo of the color code side of the Micamold capacitors in your Horiz section? Either before or after you remove them.

John

Sure, here's a pic of the 100Pf that was causing problems with the Sync Sep section.

Here's a Site that explains how to read them: http://www.tpub.com/neets/book2/3g.htm

The first (yellow) dot indicates the type the first two dots are brown and black so that equals 10, the multiplier on the second row right is brown so 10X10 =100Pf. It doesn't say how you determine voltage but I would guess it's the last dot on the lower left, black which should be 100 volts?
The Schematic lists it as a 500 volt cap.

Here's a couple more pics of that cap.
I did an Autopsy on it :D

Pic 1 shows the construction, the mica and foil are squeezed between the end connectors, a bad connection here could cause problems.

Pic 2 shows the Mica, notice the black mark on the edge of the Mica sheets, I think this was either Silver migration or some arcing that was happening, either way it doesn't look good and seems to confirm that this one was bad.

Wow, thanks for sharing the dissection of that cap..interesting observation!!

Here's a couple more pics of that cap.
I did an Autopsy on it :D

Pic 1 shows the construction, the mica and foil are squeezed between the end connectors, a bad connection here could cause problems.

Pic 2 shows the Mica, notice the black mark on the edge of the Mica sheets, I think this was either Silver migration or some arcing that was happening, either way it doesn't look good and seems to confirm that this one was bad.

Thanks, those are interesting photos! O.K., Now I know I really do need to avoid Micamold even if they are real mica. Those mica sheets don't look very healthy either. I wonder if they were like that before splitting it open.

I would have guessed that they were paper due to the white dot in the upper left corner. But, it was actually the first significant figure. I forget and mix up silver and white sometimes. It it had been silver, it would have been a paper cap and if it had been black, then definitely mica.

John

Dr Eric, thanks for those interesting post-mortem photos. From what I have seen, the Micamold caps in the flat square package which are .001uF and larger are generally just paper capacitors masquerading as silver micas. There may be exceptions, of course, and when in doubt use a silver mica. You can always replace paper with silver mica, but not always the other way around.

The paper micamolds are a fair bit bigger. My Philco had a few of those inside. I replaced them, all the bumblebees, and finally most of the silver mica caps to fix it's problems. Of course most of the instability issues were the silver mica caps in the horizontal stage, and those were the last to get swapped. I have a couple of the big flat paper caps that had simply fallen apart, no autopsy needed to see they were paper.

I decided to disect a good modern dipped silver mica for comparison. Please excuse the poor photography.

The silver sheets have ferrules that clamp the silver sheets at both ends providing a better contact than the smash the lead against the sheets technique. The actual leads are spot welded to the ferrules.

There also appears to be a thin high quality epoxy that covers the basic assembly, then that is dipped into the protective epoxy coating.

There are no air bubbles to provide an arc path.

John