Ge 21c2465

[DavGoodlin]

The U4 chassis also used the 21ESP4 and has 2kV more HV. The U4 also has a 6AQ5 for video amp and other differences. Both M4 U4 have taps on G2 for focusing
The G3 voltage (boost) for M4/21DEP4 is 310 while the U4/21ESP4 is 590.
I have a sams substitution book, but the 21DEP4 has a few subs but not the 21ESP4, The 21DEP4 shows only one sub..

[bandersen]

Hmm, that G3 could be an issue. I'm going to dig into the set right now and take a closer look at the original CRT.

[bandersen]

I got the chassis out fairly easily. Here's a closer look at the old CRT. Looks like it's seen a lot of hours.




I got the chassis up on the workbench and hooked up an 8YP4 test CRT.

It's alive Volume is stuck at 100% though.

[bars&tone]

Incredible!

[bandersen]

No signs of filament continuity from tapping the old CRT neck So, I got the 21ESP4 up on the bench for a test. It certainly works, but I don't think it's as bright as it should be considering it tests like new.

[DaveWM]

maybe just a weak video out? drifted resistors in the brightness control?

I am sure you will be checking bias voltages on the CRT to see if its being cut off.

I assume it lacks a bunch of papers?

[bandersen]

Probably all of the above It's running on what appear to be all original components and I'm sure needs an overhaul.

[bandersen]

Do you guys think I should replace the maroon caps or leave them alone ?

[Phil Nelson]

That picture looks mighty promising, but I don't have great faith in old maroon (or blue or green) drops for the long haul. That's a cool set with lots of potential -- why take shortcuts?

Phil "fix it right or fix it twice" Nelson

[kvflyer]

Bob, they very well be OK. But for the cost of new ones (Orange Drops if you please) whilst I was in there, they would go. You could always save them but let's face it. If they are gone, more done, more security. They don't cost much to replace and PC boards are easier than point-to-point replacements, don't ya think?

[bandersen]

OK, out they go. I have a healthy stock of new caps so that's no problem. I just thought I read somewhere that these caps were reliable.

BTW these board use the same post and wirewrap construction as the Predictas.

[bandersen]

My knob hunt was partially successful. The original on top has a brass insert while the two I dug up and chrome, but I'm glad to have them

[wa2ise]

And I see a 4th of those caps hiding next to an IF can on the upper left. And the black caps and an old electrolytic as well.

So, I got the 21ESP4 up on the bench for a test. It certainly works, but I don't think it's as bright as it should be considering it tests like new.

DavGoodlin above mentioned that your new CRT 21ESP4 wants something like 590VDC on I think it was G2, and the old CRT wanted about half that. Found it: http://www.bunkerofdoom.com/tubes/sy...RTS/21DEP4.JPG And the TV set chassis would be providing what the old CRT wanted, and that might be making the new CRT be dim. If so, you might be able to hack together some form of voltage doubler off the flyback winding that's making the current G2 voltage source, to make something to feed the new CRT G2 pin. Or maybe there's a source of voltage intended for focus you could use.

Try your 21CEP4, it looks like a better match http://www.bunkerofdoom.com/tubes/sy...RTS/21CEP4.JPG

[bandersen]

Thanks for the suggestions. That flyback winding is providing the boost+ voltage of around 600v and I should be able to modify the divider to get a higher G2 fairly easily.

I was planning on using that 21CEP4 in a Predicta set but we'll see how it goes.

[bandersen]

Well it turns out I had very few of the necessary caps on hand. I mostly work on older sets and only stock 630 volt caps while this set has a few 1,000 and 1,600. Oh well, I'll just have to wait a few days for my order to arrive.

Meanwhile, I discovered why the sound was stuck at 100% - the volume control is bad! There's no continuity to the wiper. I cleaned it with DeOxit, but that didn't help. Then, I pried back the tabs and opened it up for a look inside. It seems there wasn't enough pressure on the wiper so I bent it a bit. After reassembling it worked better, but there were some dead spot. Also, I managed to break the push-pull switch somehow

So I started hunting around for a 1M with 500K tap plus push-pull switch with a suitable shaft. Playthings of the Past has some promising candidates, but before placing an order I figured I better dig through my spare parts box. Much to my amazement I found an identical, NOS control right on top