Predicta: My first official Restore

[6GH8cowboy]

I have started my first restore on a predicta. Back in the day in the Biz we had an account that was a hotel that had a boatload of them. Usually just tubes and dirty tuners and an ocasional crt brightner. As a restore goes this is going to be a carefully thought out process. A previous restore left most caps tacked on top of the board and lots of glued things. The ecaps run very hot and will be replaced and all caps will be properly mounted and maybe again replaced.
There is no vertical sweep, the 3.5 meg height control is open at one end. For lack of a replacement I may swap the ends on the pcb. I was particularly amused by the wire added to ground the HO tube pin (yes the actual pin) to get the fillament to light.
The board has been pulled and the fun begins. Ive seen a lot mentioned about the hybrids. What's recomended. Are they an actual high fail item or just replace as needed.

[Electronic M]

The wire on the HOT reminds me of those pens on chains at banks and post offices....Almost makes one envision the owner doing that to keep a crooked TV service guy from stealing his new output tube.

In your shoes I'd be tempted to leave the film caps and orange drops alone...The install ain't pretty, but (assuming no cold solder joints, and that the right replacements were installed) it should work fine.

[6GH8cowboy]

After cleanup of the previous work and replacement of a small number of caps there is a fairly good picture. The sound is weak though and there isn't that sweet quiet spot adjusting the quad detector coil. I think the signal is too strong. The contrast control seems to adjust the AGC in the IF's rather than the gain of the video output tube itself. The sync buzz is very prominent on graphics. Is there a known mod for this or do these predictas do well with strong signals and I should be looking elswhere?

[Geist]

Hi All;
Cowboy, Your replacement work looks nice !! You have done a good job..
THANK YOU Marty

[DaveWM]

have you tried a new detector tube in the audio?
was the socket/trace ok?

[Phil Nelson]

Originally Posted by 6GH8cowboy

The sync buzz is very prominent on graphics. Is there a known mod for this

My 17" Siesta doesn't buzz noticeably when viewing normal content. Based on that unscientific sample of one, I'd say you should be able to get reasonable audio without circuit modifications.

The 9L37 chassis used in 21" Predictas has a buzz control -- a potentiometer on the cathode of the audio detector -- where your set has a fixed resistor. If you feel like playing around, perhaps you could substitute a little pot there and see if it helps.

Regarding the couplates (hybrids, networks), I guess it's a judgment call how many you want to replace, if any. I replaced one in my first Predicta and three in my second Predicta. These were replaced to cure problems that I observed after finishing a basic recap. The couplates that I didn't replace are still holding up years later; your mileage may vary, of course. One downside of shotgunning all of the couplates is that you'll make a crowded board even more crowded.

You can read more about the second project (a Siesta) here:

http://antiqueradio.org/PhilcoH3412L...Television.htm

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[josephdaniel]

I still need to get around to recapping mine
Every time I see a Predicta thread I look at how easy others make it look and then I look at that box of parts from just radios but then I come to my senses and realize that I will start and realize that I should wait until I have more experience! I don't even have a tube tester :p

[6GH8cowboy]

This is a 11L43 chassis and Im working from a 10L42 schematic.

The screen grid resistor on the sound IF tube V5- 6EA8 is a 10k 1 watt but the diagram says 22k. The SG voltage is correct.

Does someone know for sure what value this should be? I could just sub it but dislike soldering the pcb twice if it's for nothing.
Still fighting for good sound.

[Phil Nelson]

For what it's worth, both the Sams schematic and the Philco factory schematic give 22K for that resistor. One says 80V for that pin, the other says 50V.

Phil Nelson

[6GH8cowboy]

I went ahead and changed the bobo 10k resistor with a 22k and it helped a little. I then added the "buzz pot ( a 500 ohm trimmer) to the detector cathode and lifted one end of the existing resistor, that helped a little also. Between both, the sound is usable and fairly forgiving with strong video content. My gut feeling is the converter box is providing a very strong video signal and slightly low audio. I have noticed the low audio on the last two roundies I restored but they tuned up better than this predicta for the sound.
I'm going to let it cook for a couple of days.

I'm going to take a screen shot of the closing credits of Rock Center with their operating predicta on the shelf on this predicta.

[Electronic M]

Your converter box may have an internal volume control which varies the retransmitted sound levels. If the remote that came with the box has a volume control try turning it up and see what happens. Some exploring in the menus of the box also might prove fruitful.

[Phil Nelson]

I rarely use a digital converter, but I found that mine gave stronger audio when I switched it from stereo to mono. It was still weak, though, even with the box volume turned to max.

If you have another source to try -- a VCR, DVD player, etc. -- that might tell you whether your Predicta is truly a weakling or just not a great match with that converter.

I don't watch Rock Center, but I walked through the room when my wife was watching it the other night. I thought it was funny that they chose the very cheapest Predicta for their closing. They probably don't understand those distinctions (or care, even if they know). Whatever the set dresser likes the best, that's what they'll use.

Phil Nelson

[6GH8cowboy]

Point taken Phil. You have to admit though that for a brief moving shot it still is great retro eye candy.

[6GH8cowboy]

As I bring this job to an end I am reminded as to what a heat monster these predictas were. By adding a 4" DC powered fan on a cellphone charger to run slow and quiet, I am supprised as to how quick we go from downright hot to slightly warm. It dosn't feel like it moves much air by feel but it certainly does the job. I will likely hang from existing vent holes on a separate cord (no mod to the TV)

[DaveWM]

did you ever try a new tube? those gated beam tubes can become gassy and mess up the limiting action.