Philco 19MT79 roundie-hybrid

[Kamakiri]

This may be a stretch, but might the convergence board be the same as my roundie Philco?

[polaraman]

I pulled the convergence board. Numbers on it are: SYMB. - A
27-11014-4

POLARAMAN

[Charlie]

The one I have is SYMB-A 27-13014-1

[polaraman]

The set was reduced to rubble today. The cabinet was falling apart. I saved all the important stuff. If you need parts just give me a yell!

polaraman

[Charlie]

Polar,

I think I could use a part from your set. I stumbled across something here on accident while trying to fix audio problems.

I found the horizontal osc. coil on the deflection board is missing. Seems someone yanked it from this chassis to fix another. You'll see the coil near the 6BL8. Note in my photo where the empty spot is in the center of the photo.

I changed the transistor in the IF strip, and now the volatges in that area are where they should be. That's one problem fixed.

Right now, I'm trying to figure out why i'm not getting any output to the speaker. All of the voltages at the 6AQ5 are where they should be. The output transformer is good, tube is good, and the speaker is good. I'm not even getting any static or popping from the speaker while connecting or disconnecting the speaker leads. Usually, there will be all kinds of loud popping while touching the lead on the connection, but I am getting nothing. It seems this would be simple to figure out, but I am stumped. Suggestions anyone?

Output diagram below...

[Charlie]

Photo of missing coil for Horz.

[Jeffhs]

Originally posted by Charlie


Looks like the shop forgot to include the neck of the picture tube!

That (!) or else the last owner wanted a quick and dirty way to release the vacuum before scrapping the set. Knocking the neck off a tube will do it, but it's dangerous as all get-out if you aren't careful. Better to simply crush or literally snap off the center pin of the CRT socket with a pair of pliers, which will break the vacuum seal. I have also heard of TV picture tubes (in old sets put out for the trash) being destroyed by kids throwing rocks at the screen, eventually causing an implosion--one good hit will do it.

However, being an AK member and liking old TVs (especially Zeniths), I would never destroy a CRT in that manner if it were still good, and the TV chassis was worth repairing. The only way I'd knock the neck off or otherwise destroy a picture tube would be if the tube were shorted or the emission was so low (even with a brightener) that the picture was unwatchable, even in the dark with the brightness control at maximum.

To prevent kids and other pranksters from damaging the CRT in a discarded set, however, I would leave the back on the TV. This would not prevent anyone from using the screen for target practice, of course, but at least the neck would be protected.

[Jeffhs]

Originally posted by Charlie
Photo of missing coil for Horz.

Looks like the 6BL8 horizontal-oscillator tube is missing as well, unless the tube has been removed to show where the coil used to be.

[Charlie]

Yeah, I removed the horz tubes and many others while working on the other circuits. One reason of course is to shut down HV, and also remove uneeded tubes for the time being in case there's a problem somewhere that I'm not yet aware of.

[polaraman]

Charlie,

PM me your address and it is yours. Glad to help.


Jeffhs,

I know what you mean about the CRT. I did not do that to the set. It was that way when I rescued it from the dumpster. It is real sad that had to happen. The CTC 15 that I posted had the same thing done to the CRT. I am going to remove the face plate and use it on another CRT. Got to save at least that.


polaraman

[Jeffhs]

Originally posted by polaraman
Jeffhs,

I know what you mean about the CRT. I did not do that to the set. It was that way when I rescued it from the dumpster. It is real sad that had to happen. The CTC 15 that I posted had the same thing done to the CRT. I am going to remove the face plate and use it on another CRT. Got to save at least that.


polaraman [/B]

Sorry about that. I didn't mean to imply you broke the neck off the tube. I was just pointing out that this was a good way to release the vacuum from a dead tube; that or else snapping off the center pin of the socket (in older tubes like roundies or rectangular tubes of '50s-'70s vintage) or crushing the center pin (in the newer, "modern" if you will, button-base tubes, probably, even likely, including the CRTs used in today's sets) to break the seal. In fact, it is all too easy to break the seal on button-base tubes, since the plastic used in the socket is so thin. The necks of these modern tubes are thinner than the older ones used to be as well, making it that much easier(!) to snap the neck off if one wasn't careful--especially in large-screen tubes where the guns are set back further away from the phosphors (the larger the screen, the longer the CRT neck will be, and of course the TV cabinet itself will be that much deeper from front to back). I once saw a DuMont set in a thread here or on ebay that had a 30-inch direct-view CRT; I hate to think how long the neck of the tube must have been. The set's cabinet must have been a monster as well, but then again most DuMont consoles, even TV-only units, were huge, as were most console TVs of '50s through '70s-80s vintage with 21" or larger screens. And these were CRT-based sets. Today's giant-screen LCD and plasma sets take up much more space in a living or family room than even the largest CRT sets ever did.

I am almost convinced that one needs a living room the size of Texas or even Alaska just to be able to sit far enough away from, say, a 60" screen to get the full effect. The recommended viewing distance for a 19-inch TV is, IIRC, almost six feet away from the screen; for a 60" or larger(!) LCD or plasma, the distance may be half again that much or even double or more. Perhaps that's one reason why LCDs or plasmas aren't too popular yet--that and the prices of the sets, which are still way up there. Don't forget the maintenance costs. Plasmas (and LCDs as well) use high-power projection lamps which cost about $400 apiece and which don't last nearly as long as the filaments in CRTs (15k hours or less for the lamp, depending on usage, vs. 20+ years for many older CRTs).

Some sets have user-replaceable lamps (RCA is one, IIRC), but many if not most others require that the bulb be replaced by a service person. House calls on standard CRT-based console TVs, not to mention carry-in estimates on smaller sets, can and often do cost an arm and a leg; I shudder to think how much TV shops get for repairing today's widescreen sets (almost always house calls due to the sheer size of the TV) out of warranty.

BTW, just out of curiosity, would the set with the broken tube (or the CTC15 you mentioned in your last or a recent post) have worked if you would have replaced the CRT, or were the chassis in both sets too far gone?

[wa2ise]

About the audio output tube, I've had trouble with the volume control wiper going open circuit letting the tube grid float. I've taken care of that by connecting a 470K resistor from the grid to ground. Oh, I'll still have dirty pot trouble, but at least the tube current won't run away.

[polaraman]

Re: CTC 15. The CTC 15 is repairable. I need a few parts to do it though. A tuner is the major part I need. I also have located another really nice cabinet to put it all in. Hope to get some help from AK members to get that set going.


polaraman

[Charlie]

My audio problem turned out to be a wire to the output transformer that was broken, but was tucked in a bunch of other wires keeping me from seeing it. Looks like it was just hanging on by a thread, and most likely I was poking around and probably nudged it just enough to break it all the way.

Tonight, I had to change the first AND third I.F. transistors. After getting those out of the way, the chassis started tuning in stations. Sound is good, and you can see the tuning indicator move back and forth while adjusting the fine tuner.

Once the coil for the horz circuit gets here, I should be able to plug this into a CRT and see what happens.