56 Philco

[Adam]

I got my 56 Philco to work yesterday. I had replaced all the old wax caps and electrolytics, but it was still lacking in vert size. After checking the voltages on the vert osc. tube, I found that the plate was only 40 for 105, and the grid was +2 for -42. This first made me think that the resistors between the power supply and the vert. circuits were burned out, but this wasn't so. I put the scope to the circuits, where it was outlined in the schematics, and it was very interesting, the waveform was correct, but too small, as would be expected, but lots of duplicates kept flickering in and out, that were out of phase with the brighter original. I figured this couldn't just be a resistor, so I checked the vert osc/output tube again and it was still good. I had already checked all the tubes, replaced all the wax capacitors and checked the resistances at the tubes in the sync circuits before I had turned it on, and they were all ok. I had decided it might be that I had put in a bad capacitor, and tried replacing them again, this didn't help. I had begun to wonder about a .0068mfd mica cap connected to the grid of the vert. osc. tube same as the vert. hold control, and checked the resistance at that point on the tube again. It was only 40K for a supposed 1meg. I checked the vert, hold control seperately and it was good. At this point the only way in which this part of the tube could be connected in any way to ground was through that cap. I took it out and sure enough, it was bad. I made sure it was discharged and it still registered about 50K on my ohm meter, and rated up around .02 mfd on the capacitance checker. I put in a replacement and the set worked fine. After I had spent all day working on this set I was very happy to see it working, I think few people understand how exciting and interesting tv repair can really be.
What is odd about this is that I had checked the resistance at that point an the tube before I started the set, and it was good, which means the cap must have gone bad the moment the set was turned on. This is the first time I have ever seen one of these caps go bad, is it a common occurance?
Also I can only adjust the fine tuning to either get a really good picture or really clear clear sound. When I adjust it for the picture, there is some buzzing. Usually I can usually fix this by adjusting the AGC control, this set dosen't have one. What might I do to repair this?
And does anyone know where I might find an original volume control knob for this set?
thanks for any suggestions, Adam

[Don Lindsly]

I have a few. Provide a a part number and I'll check. If you don't have it, provide a chassis number and I'll ook it up.


Don

[nasadowsk]

Failure to get good video and sound together is either because the IF stages are misaligned, or if it's an intercarrier set like 99.9999% of the TVs made after 1950 or so, the sound IF section's misaligned.

I need to make a good accurate 4.5mhz generator to deal with the latter My big military surplus unit won't go much below 10hz, though it seriously rocks for doing FM sets. Combined with my HP counter, after a 6 hour warmup (!), you get 10.4 on the button, and stable. AN/USM-44A - heavy beast but useful...

Still need a 4.5generator though. Something stable and adjustable output. *sigh*

[Adam]

The tv is model number E4200X331. Sams dosen't give a part number for the knobs. Also, do you have the plastic piece infront of the set that says Philco behind which are the hold controls, etc.. ? It is broken, I was going to try and repair it, but would rather have a new one. -- thanks alot, Adam

I actually do have such a signal generator, I just bought an old Heathkit tv post-marker/sweep generator, solid state, looks like it comes from the early 70's. However, I lack the probes that would have originally came with it. I have the assembly manual, so I suppose I could try and make them, can you still get them? I have never tried re-alligning a set before, any information on the process would be helpful.

[Don Lindsly]

Sorry I do not have a volume knob for that model. I have some bar-over-knob pieces, but they are for models with a range switch.

Sound trouble on that TV usually comes from a bad discriminator transformer (32-4631-1). There should be plenty of those around. Make sure you have eliminated the usual suspects like the 6AU6, 6T8 and the 2uf electrolytic under the 6T8.

That TV is one of the simplest to align. The Philco service literature has the AM pre-peaking and trap frequencies marked on it. You will need a bias pack to stabilize the AGC. If you don't have one, a 9 volt battery and 100K pot will work. The RF feeds into a test point on the tuner. Connect the scope vertical to the video amp grid or detector output. Remove the RF amp to minimize interference from local stations. You can usually get by without a sweep generator. If you align the coils and traps per instructions, the curve comes out surprisingly close. Don't start until you are sure the IF and mixer tubes are all good and shields are in place. It won't line up if the bottom shield is missing or loose.

Trivia note: The "E" Model number designates your set as a '57 model year. The 330 series chassis came out in '56 and some were carried over for the '57 line.

Don

[Adam]

All the RF, IF tubes on this set were weak (except for the 3rd video IF), so I have already replaced them. The tube shields were missing, but I had some spares. The 6T8 was shorted, so I replaced it as well. The 2uf got changed along with all the other electrolytics.

How different is the bar-over-knob piece with the range switch, will it still fit with just an extra hole on the top? Mine was broken in two and only half of it came with the set. (I have been contemplating making the other half out of fiberglass) One with just an extra hole in it would be much easier to deal with, I could fill the hole with some of this plastic repair stuff I got, or just put a switch in it that dosen't do anything.

Thanks for the allignment information. It will probably be some time before I have another completely free day to try it. The sound problem actually isn't that bad, it only shows up when watching a really strong signal with alot of white on the screen at once.

[Don Lindsly]

There are several types of bar-over-knob assemblies for the 55-56 Philcos. One type snaps in place. He other is held on by two Phillips screws. Both accommodate 4 knobs. (Color and 440 are totally different.)The markings would be incorrect if you used the wrong type. The snap-on won't interchange with the screw-on without changing the mounting bracket.

Some control knobs were different shapes so the B-O-K piece will only fit on the knobs for which it is designed. I believe the 301 series uses longer knobs that are smaller in diameter. I don't remember what the 330 uses.

To compound the matter, there is also a variety of colors. I believe yours is the screw-on with longer knobs. If so, nothing I have will work. If they are the thin flat knobs, I may have something to fit if you live with mis-marked control functions. Do you have the original or can you post a picture of the knobs?

Don

[Adam]

Here is a picture of the broken piece with the knobs.

[Don Lindsly]

Adam:

I have one that looks like it will fit, but the functions will not be right. It has a chip out of it, but it is much better shape than the one pictured. You are welcome to try it.

Send me a private e-mail with your mailing address and I will send it out.

Don

[Adam]

I was finally able to get that piece back here and check to see if it would fit today. It is odd that this is just as a similar set comes up in this discussion. The knobs are a little too thick for the holes, and while they will just fit in there, they won't turn once in. But I am almost sure I can just file the holes a little bigger and it will work. This is a major improvement over trying to fix that one I had with the left half of it missing. Thanks alot Don.

[Jonathan]

I honestly never knew that getting a good picture and audio buzzing meant a misalignment. That is what might be wrong with my Sony 5-303W. I've always wondered why that occured. Now I know. On some modern sets like those cheap 5" B/W sets you find, sometimes when you bring up a station with the best picture, you get buzzing sound, but if you move the tuning knob a little but the sound gets better but the picture gets worse. Why does this happen on the modern solid state black and white sets?

Thanks.

Jonathan

[Don Lindsly]

Jonathan:

There are many causes of buzz in intercarrier sound IFs. The video carrier is AM modulated and contains high amplitude vertical sync pulses. Intercarrier sound is basically a dual superhet receiver using the video carrier for the second oscillator.

The 4.5 difference becomes the sound IF frequency. In a properly aligned receiver, the sound carrier is down to about 10% of the maximum video gain to minimize beats and hash in the final picture. The necessary gain is made up in the 4.5 mHz sound IF stages. The sound stages must have necessary gain to drive into limiting to eliminate the sync buzz. Any improper alignment or poor stage gain can result in the buzz.

The video IF must be properly aligned to assure enough sound gain as well as video bandwidth.

Sometime around the early 60s, broadcasters reduced sound transmitter power from the arbitrary 50% of video to ranges of 10%-18%. It was then necessary for the manufacturers to increase sound IF gain to compensate for the reduced power. That compounds the problem for early TVs with intercarrier sound.

In conclusion, the buzz can usually be eliminated, but it can take some methodical troubleshooting. Understanding the source is the first step.

Don

[Chad Hauris]

I have found a lot of the time just adjusting the quadrature detector coil slightly gets rid of the buzz.
I have done it by ear and it has come out fine.

[jshorva65]

Originally Posted by Don Lindsly

Sound trouble on that TV usually comes from a bad [detector] transformer (32-4631-1). There should be plenty of those around. Make sure you have eliminated the usual suspects like the 6AU6, 6T8 and the 2uf electrolytic under the 6T8.

Don

I'll take that a step further to say that the two silver-mica capacitors hidden inside the shield of that p/n 32-4631-1 sound detector transformer are the typical underlying cause of sound trouble in those sets & also make a small correction to the quote of Don's comment. Philco p/n 32-4631-1 is actually a ratio detector transformer, but mica capacitors are often hidden inside discriminator transformers & other transformer, trap, & tank circuit assemblies used in sound i.f. circuits, often without any moisture-resistant coatings. Those capacitors tend to be significantly less reliable than ordinary mica capacitors because of the open construction. We call 'em "naked micas" around here. Not all, but definitely some, makers of aftermarket substitutes for that coil designed their versions using failure analysis data from original units to determine that their versions could be made more reliable by using coated silver mica caps. The absent, weak, or noisy audio often observed as symptoms on these has become known as "silver-mica poisoning" effects. Leakage & value drift are common with the originals, including improperly-stored NOS original replacements.

Does anyone know what capacitor values Philco used inside that unit? We tried 33pF & 47pF (often-used sizes in Admiral & other brands) in a set we're currently servicing, but those values are incorrect for this set & (if I recall correctly) from a discriminator rather than ratio detector circuit. Capacitor values vary for split versus intercarrier & for discriminator versus ratio detector circuits, & will also vary according to winding inductance values chosen by individual set manufacturers.

[Don Lindsly]

Application notes indicate 83uuf, 5% between terminals 1 and 2 and 24uuf, 5% between 3 and 4, plus 8uuf allowance for varying tube and circuit capacities.
Three and four are transformer primary.

These values can vary depending on the actual transformer used. Knowing more would narrow it down, otherwise that's a start. The secondary capacitance is always more than the primary.

Make sure the CRT mount and coating are grounded.

Don