Preidcta Holiday CRT testing

[madlabs]

Hi All,

First time poster and a new Predicta Holiday owner. Before I get into questions, a little background on me. I'm a lifelong electronics tinkerer but have no formal education on the subject. I have a 'scope, variac, isolation transformer, signal gen and know how to use them. I have good soldering/remove/replace/repair skills. However, I have only a smattering of tube experience and no television experience at all. I am aware that the Predicta is a particularly difficult beast to work on. I'm not as worried about removing the PCB as I am figuring out why it isn't playing correctly.

The Predicta I got is in pretty good cosmetic condition. The plastic screen cover has scratches but nothing that can't be buffed out. Looking at the chassis, I see three replacement caps, done from the top and that's it. The power cord is broken and the power switch is broken, so hopefully it broke a long time ago and has been just sitting. The filament series resistor is un-bridged so I'm guessing that it has the 2V CRT tube. The CRT filament has continuity, less than an ohm. I can't see a number on the CRT, I'd have to take it out of the shroud. The flyback looks and smells ok.

Strategy-wise, the first thing to do seems to be to test the CRT, as if I need one of those I might as well wait to dig into this set as it appears it could take a long time to locate one. I don't have a CRT tester. I located a fellow Predicta owner who has one but his can only test 6.3V filament tubes. Can a separate 2VAC supply be used, such as a variac into a 6V filament transformer? Are there common CRT testers that have both 2 and 6v filament settings? Does anyone have one for sale?

Another way for a "proof of life" test might be to replace the caps in the power system, so as to not risk the flyback and CRT and then turn it on. Is this simply insane?

I have a ton of other questions, but for now I just need to test the CRT.

Thanks!

Jonathan

[Dude111]

Welcome to the site!!!

CRTs are georgeous..... You will have fun testing them

[Radiotronman]

I would just get a cheap bk 465 CRT tester, which can test all voltage crts and only bring $20-40 on eBay. You can usually look inside the housing by removing the rear cover. If you look down at an angle, the original Philco yellow tag will be on it and tell you the model and filament voltage of the CRT. Be careful soldering on these early pcbs. Too much heat and the foil traces will peel off. Check for any cold solder joints on the bottom of the board and make sure all traces are not broke anywhere. These are tricky sets that require patience, but having done a few myself, they're not that bad.

[oldtvsandtoy]

The few Predicta's I have worked have had a tag on the
chassis that says the picture tube is the 6.3v tube. But it may not have one. So you could start with the chassis and go from there.

[andy]

...

[madlabs]

Thanks for the replies!

I don't see any tag or markings on the tube itself. Attached to the shroud is a tag that reads: C 7100199 Part Number 319-2100. It is pasted over another sticker. I'm guessing it is a shroud number and has nothing to do with the tube.

Can the B&K 465 do the 2v and 6v filament? I know you said all voltages but I just want to be sure. I looked for a manual for it but couldn't turn one up. Since I see it recommended here and other places not to use these testers for rejuvenation, it seems that it can be done with the stuff most folks would have laying around, like in this link:

http://www.thevalvepage.com/teletech...ej/crt_rej.htm

I'd use a 6.3VAC filament transformer and use a variac to get the voltage right and use a variable DC power supply for the 100V. Does this seem reasonable? Any tips or words of wisdom or links for rejuvenating?

Just how hard is it to find a replacement CRT for this thing? I could live with one with a too long neck if need be. Hopefully this one is workable but if not how far up the proverbial creek without a motivational device am I?

No one has mentioned the idea of replacing power supply caps to prevent major damage and see if the CRT lights up? Is this because only an idiot would do that? Or because there are just too many things that can prevent raster that it won't mean much as a CRT test?

Thanks for answering my noob questions, doubtless for the nth time. I am reading all the old posts and doing as much RTFM as I can.

Jonathan

[Phil Nelson]

Originally Posted by madlabs

No one has mentioned the idea of replacing power supply caps to prevent major damage and see if the CRT lights up?

This TV does not have a power transformer, which is a major component that might be damaged by bad filter caps in the power supply. Instead, it uses a "series string" type power supply, where the tube filaments are connected in series.

This article has some restoration notes that you may find helpful:

http://antiqueradio.org/philc12.htm

The article discusses a Predicta in the pedestal cabinet, which uses the same chassis as the Holiday model.

Regards,

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

[madlabs]

Phil, I have read your page with great interest before I posted. I have it bookmarked and will re-read. I printed out the PCB layout/xray view that you have their and mine seemed different. I'll look again, maybe I was looking ta it wrong.

Is the flyback vulnerable to damage without replacing some caps? I have located a friend with a tube tester so with any luck will be able to test the CRT this week.

Any thoughts on the rejuvenation plan outlined above?

Thanks!

Jonathan

EDIT: FOrgot to add the model number of the set, G4242-M

[Eric H]

If it was me I'd just power the set up through a dim bulb tester or a Variac and see what you got, maybe jump the fusible resistor to prevent burning it out if there's a short, those things are hard to find nowadays.

There's a fairly good chance a set from 1959-60 will power up and give some sort of raster, it's probably been plugged in in the last couple years in any case because no matter what sellers tell you they just can't resist.

[madlabs]

Steve, the power cord is borked right where it attaches to the back cover. I just checked and a molex connector has the right size female connector to arrach to the set. I realize this has a hot chassis and that sticking my fingers or tongue into the set with the back removed is likely to be an owie.

The power switch is also borked. It does conduct when pressed but it won't stay in. On top of that, I'm missing the knob, so there is another possible owie. I am quite tempted to jumper the switch and try it.

Is there really no or little chance of frying the flyback or CRT without a re-cap? I'm just trying to follow the physicians code and first do no harm, as I am utterly ignorant in the TV realm.

When ramping up the variac, how slow should I go? Should I ramp it in steps? What size fuse should I use in the variac, 1-2 amps?

Thanks!

Jonathan

[WISCOJIM]

Originally Posted by madlabs

The power switch is also borked. It does conduct when pressed but it won't stay in.

That switch shouldn't "stay in". It's a "push on-push off" switch.

.

[madlabs]

Well, it is acting as a momentary switch at the moment. Press and hold and it conducts but let go and it stops conducting.

[Radiotronman]

Yes, the bk 465 is easy to use and can do both the 6.3, and 2v crts. A lot of these late 50s tvs have open sand coated Fusistors so check continuity on that also. The crts are hard to find unless you find a trashed Predicta. Be very careful testing it, because the socket in these crts use very brittle plastic and easy to bend tiny pins.

[marty59]

You mentioned about rejuvenating the CRT. I'd advise against that for now. Properly testing it is one thing at least to see what you've got. That tube is prone to being weak but it may still be good enough or usable. Unless you have a tester that has a clean function or something mild for rejuvenation don't be tempted. Even some manufacturers of testers warn about these tubes.

[madlabs]

Thanks for the tester info. With any luck my friends will do the job. And the plan is to test before rejuvenating and I'll be asking more question here before I do so. However, assuming that it needs it, any guidelines for a mild treatment?

Thanks for all the help, folks.

Jonathan