Educate me on the Predicta? - Page 2 - Videokarma.org TV - Video

Sam Cogley · #16 10-23-2010, 06:05 PM

I'll have to find someone with a picture tube tester. My Triplett emissions tester has the instructions for a TV tube adapter, but no actual adapter. The tube doesn't look like it's ever been touched - drat, I was hoping to find a nicely rebuilt tube in there.

It's a VHF-only unit, the mounting points for the UHF antenna connections are blank. I have most of the antenna, though I wouldn't mind finding the block-off plate as it will never be receiving analog TV signals again.

Front controls, broken button visible:

I have a feeling that the power switch and speaker on the back cover aren't original...

Paging Dr. Vacuum!

jr_tech · #17 10-23-2010, 06:49 PM

Quote:

Originally Posted by DaveWM

I would check the CRT, careful on the filament voltage, not sure what it is.

Indeed, be careful, my GE tube manual says that the 21EAP4 has a 2.34 volt 600 ma heater.

jr

DaveWM · #18 10-23-2010, 07:31 PM

looks like the adams family moved into the cabinet.

Pretty sure its a series string set, so be careful.

I would start by pulling the chassis, use some compressed air to blow out most of the dust, then use q tips and your fav solvent to clean the rest.

after that you can asses how to tackle the recap (above board or pull the board).

Since its your 1st one, I would recommend going with above board j hook or pig tail, so as not to disturb the wiring.

After a basic recap of all the papers, I would check the filters, they maybe ok if so you can try a slow power up with the HOT and VOT tubes pulled out of the sockets, check the filter cans for heat and watch the input current on the ac line. I like to start out slow, maybe 10-20vac and check the b+ if each B+ leg is looking good, then go up to 40vac and keep an eye on it. again watching for heat/current on all the filter caps and B+ rails.

Dont go much over 60vac since with out the HOT there will be no load on the B+ and it can go too high.

you can also just check the resistance at the B+ (power off of course) to look for shorts. Just a WAG but I would think 10k or more. If its a lot less then I would suspect a short (it should rise some as the filter cap charges from the current in the ohm meter).

I just went thru this with another set, one of the lower B+ legs was 240 ohms to ground. It had taken out a big dropping resistor. Traced the short by disconnectig the B+ until I found where the short was (the B+ daisy chained around, so you could unhook a section and see if the resistance popped up, if finally did, turned out to be a shorted disck bypass cap).

anyway if your B+ resistance checks ok, and the filter caps dont heat up at 60vac line voltage, and the current was low at the line (no other shorts), then I would let everything cool down (all the tubes since they would be warmed at athe 60vac) plug in the HOT and VOT, and do another power up. This time go right to 115vac relatively quickly (seconds) keep an eye open for filaments and monitor the the B+ if you can.

Series string stuff scares me and come to think of it , the other tubes prob will not be warmed up since you pulled the HOT and VOT, but the B+ should still be there during the testing phase since I am sure it just uses a SS doubler.

Sam Cogley · #19 10-24-2010, 12:09 AM

Quote:

Originally Posted by DaveWM

looks like the adams family moved into the cabinet.

Pretty sure its a series string set, so be careful.

I would start by pulling the chassis, use some compressed air to blow out most of the dust, then use q tips and your fav solvent to clean the rest.

after that you can asses how to tackle the recap (above board or pull the board).

Since its your 1st one, I would recommend going with above board j hook or pig tail, so as not to disturb the wiring.

After a basic recap of all the papers, I would check the filters, they maybe ok if so you can try a slow power up with the HOT and VOT tubes pulled out of the sockets, check the filter cans for heat and watch the input current on the ac line. I like to start out slow, maybe 10-20vac and check the b+ if each B+ leg is looking good, then go up to 40vac and keep an eye on it. again watching for heat/current on all the filter caps and B+ rails.

Dont go much over 60vac since with out the HOT there will be no load on the B+ and it can go too high.

you can also just check the resistance at the B+ (power off of course) to look for shorts. Just a WAG but I would think 10k or more. If its a lot less then I would suspect a short (it should rise some as the filter cap charges from the current in the ohm meter).

I just went thru this with another set, one of the lower B+ legs was 240 ohms to ground. It had taken out a big dropping resistor. Traced the short by disconnectig the B+ until I found where the short was (the B+ daisy chained around, so you could unhook a section and see if the resistance popped up, if finally did, turned out to be a shorted disck bypass cap).

anyway if your B+ resistance checks ok, and the filter caps dont heat up at 60vac line voltage, and the current was low at the line (no other shorts), then I would let everything cool down (all the tubes since they would be warmed at athe 60vac) plug in the HOT and VOT, and do another power up. This time go right to 115vac relatively quickly (seconds) keep an eye open for filaments and monitor the the B+ if you can.

Series string stuff scares me and come to think of it , the other tubes prob will not be warmed up since you pulled the HOT and VOT, but the B+ should still be there during the testing phase since I am sure it just uses a SS doubler.

Thanks for the suggestions! I have a few tube audio projects that need in line in front of the TV, so I'll have some time to accumulate info before digging in. This might be my first television, but I've been slinging solder for a while and I've been into tube audio for a year or so now. I'm not afraid of pulling the boards to do it right.

Sam Cogley · #20 10-24-2010, 10:20 PM

Part of me is itching to drag the Variac over and see what I'm dealing with...

Sam Cogley · #21 10-25-2010, 01:29 AM

Gave it a spin with the Variac. Nothing doing. The pilot light came on, but I couldn't see any glowing tube filaments through the grilles, and the picture tube didn't do anything. I would assume that at least one tube is shot, I should have spares for all of them.

If anyone has a complete "shotgun" list of parts for the Predicta Holiday, I'd greatly appreciate it. My feeling is that 52-year-old carbon comp resistors are probably due for replacement, and there is no need to futz around taking the boards in and out. Fix it once, get it over with.

leadlike · #22 10-25-2010, 07:15 AM

These things have a soft start thermistor as well, it's likely that went open, and that would kill the filament string as well.

Below is a rare thing to find online-a free Sam's Photofact folder for your set (no affiliation):

http://www.nappepin.com/predicta/predicta.htm

***Eric H*** · #23 10-25-2010, 08:16 AM

ETF also has Schematics posted for this set, and others. http://www.earlytelevision.org/tv_sc..._diagrams.html

Sam Cogley · #24 10-25-2010, 11:11 AM

Thanks, guys! Anyone know of any errors in the Sams parts list for the G4242?

Phil Nelson · #25 10-25-2010, 11:42 AM

I didn't notice any errors, but I didn't replace every resistor.

Phil

bgadow · #26 10-25-2010, 10:10 PM

There is probably a fusible resistor in there; mine was pretty ugly/corroded and was keeping the set dead. You could hunt around for a replacement (Workman sold them, among others) or make up something with a wirewround.

Phil Nelson · #27 10-25-2010, 10:47 PM

IIRC, my barberpole had both a thermistor, aka "surgistor," on the AC line and a fusible resistor, aka "fusistor," somewhere near the flyback (although I don't remember exactly what it connected to).

For a thermistor, I have used either CL-90 or CL-60 on various sets. For that fusible resistor, I wired a fuse in series with a power resistor of the needed value.

Phil Nelson

Sam Cogley · #28 10-26-2010, 10:13 AM

What exactly does that dual concentric knob on the front do? Volume and power? I assume something is wrong with the power switch, as one was grafted onto the back.

Don Lindsly · #29 10-26-2010, 11:42 AM

Center control is off-on-volume, outer control is contrast.

Sam Cogley · #30 10-26-2010, 11:55 AM

Quote:

Originally Posted by Don Lindsly

Center control is off-on-volume, outer control is contrast.

Is it a push on/off, push-pull, or turn type of power switch? From futzing with mine, I would guess that it's push on/off, and the retainer is busted.