Predicta Holiday - First power up attempt

[madlabs]

Once again I misunderstand basic terms. I'll get there...

Boy, am I glad to hear there is still hope for the 21FAP4. So:

As noted, I swapped pins 2&3. Looking at the 21FAP4 data sheet it says pin 6 is I.C. I read that as not connected. On the 21EAP4 both pins 2 and 6 are connected to G2. I am using a CRT socket and harness from a set with a 21EAP4 and it works fine with a 21FDP4. So, if I am getting this, I can't swap pins 3&6.

As I sit here at work away from the set, now I wonder: Does the CRT connector use pin 6 or 2 for the G2 connection? Maybe I need to change that or jumper pin 2&6? Man, wish I could look at that right now...

[bandersen]

I'm not suggesting you connect anything to pin 6 for the 21FAP4. You say you have a 21FDP4 in there now. Take a look at the data for it. It shows G2 as pin 6. So try switching the wire on pin 6 to pin 3 and the wire on pin 2 to pin 3.

[madlabs]

Originally Posted by bandersen

So try switching the wire on pin 6 to pin 3 and the wire on pin 2 to pin 3.

Thanks for your patience Bob. But the way I read the above I would be putting two wires to pin 3. Did you mean swap pin 6 to 3 and pin 3 to pin 2?

[Electronic M]

I believe he is discussing purely pin swaps. Compare the two base pin outs (side by side preferably) of the data sheets below (it ain't rocket surgery). If it originally had one tube in it and now has the other then you need to swap wires so that the one wired in the set's chassis for G2 goes to the G2 (G2=Grid2) pin on the tube you have in there now. You will need to confirm G1, K(cathode), and possibly others.

https://frank.pocnet.net/sheets/168/2/21FAP4.pdf
https://frank.pocnet.net/sheets/049/2/21FDP4.pdf

If you connected your car battery backwards would you expect your car to work? The pin outs of the 2 tubes are different so the socket wires have to be swapped until they match the pin out of the tube you have in there.

[bandersen]

Originally Posted by madlabs

Thanks for your patience Bob. But the way I read the above I would be putting two wires to pin 3. Did you mean swap pin 6 to 3 and pin 3 to pin 2?

Yeah sorry. Pin 3 to pin 2. As Tom said, carefully check the wiring and make sure it is correct when you have the 21FAP4 installed.

[dtvmcdonald]

Don't ever ever just swap.

Trace out the wires to their source and connect up according to the
data sheet of the new tube.

Paranoia in this business is usually the best policy. Knocking on
wood is good too.

[madlabs]

I can hear the frustration and I'm sorry for being thick. Sadly, tat is exactly what I was trying to do and I did indeed compare the sheets. I think I may have found the problem and will verify when I get home, but what I think is this:

One does indeed need to swap 2&3 as I did. The 21EAP4 (the data sheet I was comparing to) shows G2 on both pins 2&6 and the 21FAP4 shows it on 2 only and pin 6 is I.C.. I'm guessing that the socket has G2 wired to pin 2 and nothing to pin 6. I'll look when I get home.h

[madlabs]

OK, back home and had a little time last night to play. I think where I went wrong with the 21FAP4 was that I didn't check which pin they were using for G2. On the 21EAP4 you can use either as both are connected to G2. I assumed (and we know what that makes me!) that they used pin 2 on the CRT socket but in fact they used pin 6. So a straight wire swap won't work, one needs physically move the wire to pin 2.

So, what I did was remove the two rivets that hold the disc that keeps the contacts in place in the socket. Now I can mix and match locations at will. I have some #4 brass bolts that fit nicely to put it back together. Sadly, real life prevents me from doing it today but I will tomorrow.

Some related questions: The last time I tested the FAP4 I just had it loose, no holder on it. How stupid is that? I was reading that part of the holders job is to prevent flying shards in case of an implosion. I was wearing eye protection and did drape a towel over it when moving it around. Since I am pretty sure the tube is good, I was thinking of putting the holder from my 21EAP4 on it but the idea of doing that puckers me up. How does one tension it correctly so that expansion and contraction don't make it go boom? There is the perimeter strap and the two straps that go around the back. Which order should I attach the straps? Any tips on this would be much appreciated.

I really appreciated the patience and help guys. I know I'm a little thick but I really am trying to learn how it all works.

[bandersen]

What we were getting at is that you've got a 21FDP4 installed in your set so forget about the 21EAP4 datasheet. The FDP4 shows no connection on pin 2 so it had to be using pin 6. I bet your FAP4 will perform like a champ when you get it wired up right.

By holder I assume you mean the safety plastic screen cover ? Yeah, it is there for implosion protection. Now I can't be irresponsible and tell there is zero risk, but I think we've all routinely ignored it. Personally, Ive got a couple dozen loose CRTs lying around in and out of of shipping boxes.

As for the band, I make a note of how tight it is before I take it off and try to get it the same when the new CRT is installed. Maybe mark the bolt with a sharpie. As I recall the straps all go one as one piece ? I only loosen the bolts on either side of the band that goes around the face of the CRT and slip the CRT out.

2016-03-23 002

[madlabs]

Yeah, I got confused between the data sheets and whatnot. Wrote it all out and drew a diagram and I think I have it now. Taking the retaining disc off the socket will make it easy to get it wired right. Wish I could do it today, I really want to know!

By holder I meant the straps and bands, not the plastic face. Marking the bolts with a sharpie sounds like a great idea. Looking at it again I see what you mean, loosen the perimeter band and I should be able to leave the other two alone and slip the tube out.

Thanks again!

[Electronic M]

I always go with somewhere a bit beyond snug enough to keep it from being knocked out under the harshest drop that the CRT might survive....If it feels like your crushing the tube with the band then it's time to loosen it a bit.

Expansion/contraction is not much of a concern unless you are keeping it outside or let your thermostat drift a lot.

Marking the bolt on the band while valid can be a bad thing...There was manufacturing tolerance in bulb size (especially from maker to maker), and I've heard of cases of people on tube swaps in other sets doing that and having implosions due to over-tightening to set the band bolts at the same number of turns with a slightly larger CRT.

I tend to slip a screw driver under a gap between band and CRT and carefully/gently pry to see how much give/movement the band has...That gives me a feel for the tension.

[bandersen]

Good points. Also, you may have been reading about tension bands offering implosion protection. That is most certainly true of more modern color CRTS but not old B&W CRTs. That band is really there just to hold the CRT in place.

[madlabs]

In the event, it was pretty easy to put the bands on. You can tell when you have it right.

And the 21FAP4 is working GREAT!!!!

As I said above, I removed the rivets that hold the disc on the CRT socket and that allowed me to easily play mix and match. What needed to be done was:

Move pin 3 (G1) to pin 2
Move pin 6 (G2) to pin 3

I can't believe how much better it is. The focus wire actually does something now! I haven't started tweaking it much but the linearity looks better already. Much better detail in credits and stuff with writing. Very, very cool.

I start to think that I might wind up with a good looking, good working Predicta. Been a long road with many mistakes and even a fire but there is hope! Thanks folks, never woulda happened without y'alls help.

EDIT: Guess I better fill in and send the warranty card into Sylvania!!

[madlabs]

Merry Christmas all!

Getting in a little time today and I while playing with the focus jumper I noticed that there is 430V instead of 280V on the high side of the jumper. When connected to that I get a crisp picture but the lines are too visible. Looking at the schematic I see it goes to R37 (47K) and then to the 435V boost supply. R37 is in a dotted box, like the couplates. And there are two X's, one on either side of the resistor. What is that all about? Is it possible to use a pot of say 50K to fine tune the focus?

I'll go look into why the voltage is too high. Such a pain to take voltage measurements and whatnot under the chassis of this set.

[tom.j.fla]

The x's and dashed lines mean circuit changes, some sets have them some don't. As for the pot, 50K is too small, use a 1meg. min. for a focus pot one end to boost other end to circuit ground center pin to focus lead to CRT. All the best, Tom.J