Preidcta Holiday CRT testing - Page 2 - Videokarma.org TV - Video

Electronic M · #16 07-11-2016, 09:23 PM

If you variac it keep ambient light low and watch the plate of the H output tube...If it starts to glow then your fly is in danger.

I normally start the variac at 20-40V and step it up in 5-10V increments every 1-20 minutes....The newer the set/shorter it has been dormant the more aggressively I crank it up.

The CRT ID number will be 2 digits 2-3 letters (ending with a "P") followed by 4 (and possibly another letter)...For example "21EAP4". Most monochrome CRTs end in 'P4' and most color in 'P22'.

madlabs · #17 07-11-2016, 09:55 PM

Mike, thanks much for the information. Very good to know to watch for the H tube plate and I'll ramp up real slow. First thing is to test the CRT. My buddy with the tester was on his way out of town and couldn't recall the model, so hopefully what he has will work. Once I have some test results I'll report here and see if rejuvenating is recommended.

If it passes I am torn between doing a total recap all at once or seeing if it works and replacing the caps one section at a time. I like the thought of doing it one section at a time, makes it easier to figure out if I screwed something up along the way. If I keep a sharp eye on the h tube plate, have an appropriate fuse inline and watch the current draw, how risky is it to try to light it up?

Also thanks for decoding the tube numbers. However, I'm guessing that not all 21" monochrome tubes will fit the plastic CRT cover. I haven't been able to find a list of Predicta subs. I could live with a tube that pokes out the back if need be.

Thanks!

Jonathan

Electronic M · #18 07-11-2016, 11:04 PM

On PCB sets save your self the trouble of tediously removing and remounting the board repeatedly, and just do the whole board in one go....Resistors that are out of tolerance should go, and maybe the couplates if you are in that camp.

Caps off the board are fine to change in any manner that works for you.

madlabs · #19 07-11-2016, 11:14 PM

Oops, I see I somehow called you Mike, Tom. My apologies.

And duh, I wasn't thinking of the way the PCB is mounted. So yeah, gonna hafta do them all at once.

What is your take on the couplates?

Jonathan

madlabs · #20 07-12-2016, 10:09 AM

Another question: Where is the CRT usually marked? I can't see any markings looking in through the back. Might removing the socket reveal them? Or do I have to take the tube out of the shroud?

Jonathan

N2IXK · #21 07-12-2016, 10:14 AM

The tube number is usually on a paper label stuck to the side of the funnel shaped part of the bulb. It is somewhat common for it to have fallen off and be laying loose inside the shroud.

As far as the couplates go, I would recommend replacing them while you have the PCB out. They are cheap enough to rebuild/replace, and saves all the work of pulling the board again. I believe Bob Andersen (bandersenTV) sells reproduction units already built.

Another common trouble spot on these sets are the tube sockets on the board. They are prone to cracking of the metal contacts, resulting in intermittent operation or outright failure. Check them carefully while the board is out and replace if needed.

holmesuser01 · #22 07-12-2016, 01:05 PM

I have always considered a rejuvination to be the absolute last resort with a CRT. Too many other things that can cause a dim dull picture.

Please resist temptation to do a rejuv. Often, this will destroy the tube.

WISCOJIM · #23 07-12-2016, 05:26 PM

Quote:

Originally Posted by holmesuser01

I have always considered a rejuvination to be the absolute last resort with a CRT. Too many other things that can cause a dim dull picture.

Please resist temptation to do a rejuv. Often, this will destroy the tube.

Absolutely. A full and proper restoration first, then assess the tubes quality.

.

Electronic M · #24 07-12-2016, 07:44 PM

Quote:

Originally Posted by madlabs

Oops, I see I somehow called you Mike, Tom. My apologies.

And duh, I wasn't thinking of the way the PCB is mounted. So yeah, gonna hafta do them all at once.

What is your take on the couplates?

Jonathan

I've personally never worked on a predicta (I'll explain later), but have worked on a few other period sets that use that style of couplate. Personally it depends on how much I'll use the set and how much money and effort are involved...I'll often just see if the couplates are good (have not had a dud yet), and leave them be if they work. If I was restoring a set for a client I'd probably change them just to lower chance of a call back. I probably would not be as phased about board removal on a predicta as some other restorers (who harp on it), but if it somehow really became a pain I'd just change the couplates to save me a headache.

The CRT ID is usually on a paper tag on the bell of the tube, but sometimes if the tube has a bakelite base the number will be there too.

I don't own a predicta because I feel they are the '57 chevy of vintage TVs....A common average performing set that people buy up and pay stupid money for despite the engineering, etc. being nothing special...Yeah they look cool, but there's a lot of other sets of the day that are cooler, rarer, and don't have a crowd of fanatics driving the cost of one skywards. If I find a cheap one (I do have a lead) or the Penthouse model (which is cool, especially the engineering, and rare enough to interest me) once I have cash, then I'll own one.

madlabs · #25 07-12-2016, 08:35 PM

Tom, When I was a kid a saw a Predicta and somehow fell in love with it. I can see what you are saying though. Another plus is that the XYL loves the set too and wants it in the living room. They do go for stupid money, I paid $250 for mine and drove 4 hours each way to get it. At least I didn't have to pay shipping and risk having it smashed.

As to the couplates, I do plan to use the set weekly. I don't watch a whole lot of TV and in fact don't even own a TV at the moment. I guess I am leaning towards replacing the couplates. I'll do some more looking around at what it takes to make them and I heard that banderson of this forum sells them.

I have seen a thread about putting connectors on the PCB/wire connections but the poster didn't in the end. Seems like it might be a good idea. While this set won't see a ton of hours I do plan on using it for years to come so it might save time in the end. Thoughts?

I may have found a NOS 21AFP4 picture tube that may work with this set, either to replace the one in it or as a spare. I am still trying to determine how much has to be done to use this tube but considering the only way to get a "proper" tube is to buy another set and hope the tube is good. So unless it is too complex to do the required mods it seems like a good investment. I have started a separate thread on that topic.

Thanks so much for taking the time to answer what is doubtless painful noob questions. I do indeed appreciate it.

Jonathan

Phil Nelson · #26 07-12-2016, 09:39 PM

Quote:

Originally Posted by madlabs

I have seen a thread about putting connectors on the PCB/wire connections but the poster didn't in the end.

The following article has a section discussing the pros and cons of installing quick-disconnect connectors on the big PC board:

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

Scroll down to "Adding Quick Disconnects to the PC Board."

As explained in the article, I decided that the cons outweighed the pros. A thoroughly restored Predicta should not need frequent service that will require pulling that board out repeatedly.

Regarding the couplates, on any other TV I'd recommend leaving them alone and waiting to see how the recapped set behaves during a prolonged bench test. Having restored two Predictas, and recalling how much I disliked removing and reinstalling the big PC board, now I would lean toward replacing them preemptively. The article referenced above has sections on replacing couplates, but notice that it describes a different Predicta chassis than yours. The following article mentions couplate replacement in the pedestal/Holiday chassis:

http://antiqueradio.org/philc12.htm

As seen in the photo below, the couplate replacement can be simple -- a few parts wired onto a chip of perf board.

Regards,

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

Regards,

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

madlabs · #27 07-12-2016, 09:55 PM

Phil, thanks for the link, great write up. I think I agree, the cons outweigh the pros concerning connectors. As to the couplates, that looks too easy to risk having to pull the board again.

And I forgot to reply earlier to Bruce and Wiscojim, I will NOT rejuvenate until the tube is tested and shows dead. And in that case I will seek advice on the best way of doing so.

Thanks!

Jonathan