WAY OFF TOPIC, BUT WTH...

[jingle_jangle]

Ladies and gentlemen:

I've got a loverly 1959 Philco Predicta television set that was completely over a long period by a gent in Tennessee who is now out of business.

You can see it in this photo:



Problem is that, despite nearly everything functional having been replaced, and it's only having had about 12 hours of use, the picture died completely although sound is fine.

Does anyone have a clue about how to go about getting this beauty diagnosed and/or repaired? I have schematics, alignment instructions, and some troubleshooting information, but am hesitant to do anything and so I'm in the dark and apparently stuck in an area where plasmas rule and nobody speaks tubes anymore.

[libratune]

You might explore around here. The most relevant books listed are primarily about the "history of radio" but they also reference the development of tube television:

http://www.tubesandmore.com/

[manta]

A large hammer works out here in the islands.

But we only watch re-runs of our hero Gilligan!!

Timbo

[woodyng]

there's a tv in that picture? tell me about the guitars! (very cool,esp.the tv)

[cjj]

The first thing to check when the picture is gone is whether the high voltage supply to the picture tube is working. Without the high voltage, usually somewhere around 20kV, there's no incentive for the electrons to leave the gun and smash into the phosphor to light it up. Oh, I suppose the first first thing to check would be to see if the cathode filament is lighting up, the orange glow you see in all tubes, it would be at the far rear end of the picture tube, opposite the screen.

WARNING: DANGEROUS and possibly stupid instructions ahead!!!

Anyway, back to the high voltage. Testing this is NOT for the foolish or faint of heart. It probably won't kill you, there's generally not enough current available, but, depending on the particular TV, it could kill you. In any case, if you get shocked by it, it will hurt like hell. Don't ask how I know. OK, I'll admit, I've gotten whacked a few times over the years fixing TV's and video monitors.

If you don't have a high voltage meter, a quick and simple way to test this is to take a long thin screwdriver with a plastic handle, attach a wire firmly with something like alligator clips between the screw driver and the chassis. Carefully push the tip of the driver under the rubber cap at the end of the big wire going to the side of the picture tube making sure you hold only the plastic handle of the screw driver. This can actually be done with the power off, just make sure it hasn't been off a long time. The voltage will still be there for a few minutes (or even days in some sets) after power is off. If there's high voltage, you will hear a loud snap as it arcs to the screwdriver. If the power is on, you will continuous arcing, don't leave the driver there too long.

If you don't have any high voltage, the most likely cause is that the horizontal sweep oscillator is bad. I don't know about Philco's, but in nearly ALL TV's the high voltage is generated with a "flyback transformer" from the horizontal sweep oscillator. In tube type TV's there is generally one tube that runs the horizontal. This tube a bit prone to failure because it's working pretty hard oscillating at 15.75kHz. By the way, if you still have good hearing, you can generally hear the 15.75kHz squeal of the oscillator running. If you've replaced the horizontal tube (I assume those old Philco's were tubes, right?), there can be a number of other things, the HV circuit will have a diode, which if bad will cause no picture. You won't get much, if any voltage either since the diode is an integral part of the way the flyback circuit works. It could also be the flyback transformer itself, these do go bad, but it's fairly rare in older sets. They were built tougher back in those days.

Well, that got a lot longer than I thought. I'll end it there, but feel free to ask for more if you want...

[jps]

A friend of mine here can repair it.

[kiramdear]

Yeah, ditto.

[jingle_jangle]

CJ, what you've given me is a great beginning. I have heard that oscillation "squeal" on this TV (it was nostalgic to hear it the first time I switched it on!), but when it failed, which was back last October, I failed to note if it was still making that sound. That's #1. If squeal is present (I doubt it), then I can get the electron gun cover off the back of the tube shroud, and will be able to see if there's a filament glowing in there. The horizontal oscillator tube is a very common 6CG7, but the video output tube (more probably bad) is an oddball 6AW8A. The presence in my shop of a bunch of RCA tube manuals (most recent is 1960) has been a bit of a help, too. Previous owner of this house (Harry J., passed on in 2003) was an electronics engineer (as I mentioned to Kira once, he was the chief engineer on the Sutro Tower here in SF, which in an unsightly engineering marvel we couldn't do without. Harry was his name, and I wish I was as versed in electronics as he was, but, then, he couldn't build guitars so that's that.

There is also a 5.6KΩ "fusible resistor" protecting low voltage circuits, but it seems to me if that's dead, so would be the sound, and sound is fine. These TVs are considered repairmen's nightmares due to the density of componentry and early use of fiber PC boards. I did a quick visual inspection when I had the chassis out of the cabinet when it was first shipped back to me, and all the transformers looked new, boards were like new and it was obvious that it had been gone through thoroughly.

Interesting to me was the fact that, when I first turned it on--hooked to a hidden DVD player stuffed with old B & W movies, there was a definite IF detector buzz with some source material. Fine tuning eliminated most of it, but there were also problems with sweep, but only with wide screen material (probably an incompatibility in scanning info between the DVD player and the set itself).

Now I've discovered that there are three adjustments that I can do with an alignment tool, and the adjustment points are under each of the three knobs on the cabinet's side! In other words, you pull off the knobs, insert an alignment tool into the center of the knob's hollow shaft, and twiddle away. These adjustments are for vertical linearity, height, and horizontal range, and should have been tweaked before I put it into service initially.

More on Harry's house: he had it built in 1955; it's smallish for a CA house (only 2000 square feet) but has 1000 feet on the lower level of shop, display, and storage space for my guitars. The shop came equipped with hundreds of Harry's parts bins and two large and very well-built benches and oodles of hand, power, and gardener's tools, which I bought from Harry's daughter for $1, not to mention much of Harry's electronics library, much of which is Greek to me. None of it is in the nature of a primer on complex tube TVs, unfortunately. Lastly, I do have a feeling of Harry's benevolent presence in the shop when I'm working there late at night, and his bins have always managed to come up with the odd part--including low-voltage bulbs in the exact quantity and type needed to complete a rebuild of a LS that was in for repair!

Anyway, I'm going to have a look at this over the weekend. I do have a hunch that this is an easy one, so I'm happy to be pointed in the right direction. Thanks again CJ, and I'll be in touch.

Jeff, thanks for the offer, but at this point I hesitate to ship it again across country, as it's been to Knoxville and back to the West Coast already, with zero damage.

Kira, that guy Charley's daid. And I don't feel his presence, fortunately.

[cjj]

Yeah, if the video amp tube is gone, that would lead to no picture too, but in general, on the old tube type sets you might see some flickers of light when the set is turned on or off. This can happen with HV problems too so it's always best to check out the HV first.

Now, it's possible to hear the squeal and still not have HV. The flyback circuit is a pretty tightly tuned circuit and, if the horizontal frequency is off too far, it won't work. You might hear a squeal, but unless you have perfect pitch in the 15kHz range, you wouldn't be able to tell.

Anyway, there are a whole list of things to check after the HV, but we can get to those if/when it's necessary. As for the video tube, the 6AW8A, I can't say I know much about those, it sounds kinda familiar, but I really haven't done a lot with tubes for 30 or 40 years. You know how that memory thing works. Anyway, with some specs on the tube, sometimes you can find a way to work around it. I had an old Halicrafters short wave radio from the 1930's that needed a tube that was no longer made (a dual diode/triode). I found a suitable triode and rewired it with solid state diodes, not original, but it worked great.

Edit: As I like to say, google is your friend!

Here's a list of suitable replacements for a 6AW8A:
6AU8 6BA8 6CX8 6EB8 6HF8 6JE8 6JT8 6JV8 6KS8 6KV8 6LY8

Here's a place that says they have 6AW8A tubes for $4.95:
http://www.tubedepot.com/nos-6aw8a.html

Oh, and cool story about your house, etc.!

[kenposurf]

I know someone up here in Larkfield that can fix it for you Paul

[jingle_jangle]

CJ, I'm going to do as much as I can with my limited resources here. I've used Tube Depot for odd tubes for my Maggie amps. I'm going to do basics like check the tube seating, filament glow (visual), and have a look at the plug and umbilical for the picture tube.

If, after plodding through the basics with your assistance, CJ, I still am stymied, I'll run it up to George's guy.

[jingle_jangle]

there's a tv in that picture? tell me about the guitars! (very cool,esp.the tv)

Woody:

viewtopic.php?f=5&t=388012

[aceonbass]

Amazing Paul! You have a Television that was actually MADE in the USA! Whodathunkit?