21cy Into Ctc-4 Mask

[stromberg6]

I have a CTC-4 in which I would like to use a 21CY in place of the 21AX. Can someone tell me if the newer tube will fit in the mask? I have a fair 21AX, but might need to use it in a CTC-5, as the conversion to a glass tube looks more difficult than with the 4. Also, the HV connector for the CTC-4 has had its' metal spring pieces broken off. Anyone ever repair one?
Thanks, Kevin G.http://www.acuramdx.org/forums/image...s/confused.gif

[blue_lateral]

No personal experience with this, but I have read about it, a long time ago. Here's how I think it is, you can take this with a grain of salt..... memory foggy.....

The shape of the front of the tube is different. The 21ax has a flatter screen. The 21cy (and the 2ifb, and the 21fj) have quite a bit more roundness. The mask doesn't fit. The contour around the edges is wrong. I suspect the tube will go in, but it will look funny.

RCA made mount kits to put the 21cy in those older sets. They included a new mask. I'll bet that would be a tough to find part now.

Good luck,

John

[stromberg6]

Thanks John. The face of the 21CY does seem to be "rounder". I guess I will try the 21AX with the weak blue and green guns. Funny thing about this crt is that the red gun measures as new.
Thanks again for the reply.
Kevin G.

[pallophotophone]

Perhaps the green and blue guns simply need to be run in for a while. Filament only with no B plus as in a tester environment.

Just a thought.

[kx250rider]

I agree about trying to use the 21AX. However, I'm not sure about how bad the fit may really be with the glass tube installed. I have had a number if 21AX-designed TVs with glass tubes installed, and I don't remember seeing any glaring mis-fit.

The tech issues to deal with would be to remove the field magnets from the mask, and replace the anode lead end with a regular glass tube-type one. Also you should remove the 25KV doorknob capacitor from the bottom of the HV rectifier tube and add an aquadag ground wire/spring. All of the above are reversible in case you go back to the metal tube later.

Charles

[John Folsom]

The 21AXP22 datasheet shows 26 1/4 " faceplate radius of curvature, the 21CYP22 datasheet shows a 26" radius, so I would not think there would be much of a mask issue, as Charles noted above. But I have mpt tried this substitution myself.

John

[stromberg6]

Thank you all for the replies!
I am taking a long weekend over the Presidents holiday period. I will attempt to install the 21CY, and let all know how it goes. I am currently working on a solution to the HV connection, which shouldn't prove too difficult. The "leaves" of spring steel have broken away from the center of the connector disc. I am going to try to attach a suitable piece of HV cable, using a #4 screw, by inserting the screw between the broken pieces left in the disc. No HV putty on hand, but lots of corona dope and RTV compound (BTW Cool Whip tops with HV putty wedged between once served well in a 21FB conversion in a CTC-7 near the anode and crt mounting ring).
As for the weak 21AX, I have had the heaters on for a couple of hours during initial testing, but will keep them on longer to see what happens. Thanks for that suggestion!
Thanks again!
Kevin G.

[stromberg6]

I "fired up" the 4 on Sat 2/17, and I am attempting to attach a couple of screen shots. The color won't sync, and only preliminary adjustments have been made, but it did not smoke, and the 6CB5 is not glowing red.
I used a 21AX that tested very good on a borrowed RCA crt tester. I guess mine is giving false readings. More info to follow as the work continues.
Kevin

[kx250rider]

On the color sync: First and foremost, be SURE all of your shield cans are in place. Those CTC-4s are hypersensitive to the point where even rotating a shield can can throw things off. Len Horowitz once commented that moving a metal object near the set can change the alignment!

Also, I wouldn't try to move any coils until all of the tubes are verified strong, and the color section has been recapped.

Charles

[stromberg6]

Thanks Charles, I think I have a signal strength problem, maybe with the tuner. The pix is not smeary, but isn't as "sharp" as it should be. I bought some NOS 6AZ8's and a 6X8 at a swap meet Sunday, so I will change around the osc/mixer and video IF tubes and see if that makes a difference. Also don't like the 6AN8 reactance tube. I have a bunch of those.
The only control I have touched so far is the AFC pot to see if the chroma would lock in. I learned early on NEVER to take a diddle stick to anything without the proper set up of test equipment. A friend who just finished a 4 for someone has offered to set it up on his bench and go through it. Should be interesting to see what the old timer is capable of.
The pix would not post. File size exceeded was the message.
All the best,
Kevin G.

[julianburke]

Back in the sixties, I used to put 21FBP22's in CTC4 and CTC5's and they fit nicely with no modifications. They also work very nice!! Be sure to screw in the purity magnets (to neutralize them) around the bezel if you don't want to remove them. Julian Burke

[stromberg6]

Thanks Julian! I have a 5 that may get a 21CY. Checking voltages at the burst amp and 3.58 osc, I found them to be low. I found that the 380 and 285 volt sources are low, 335 and 265 respectively. color will lock in, but lock is dependent on level of chroma signal as varied by "color" control. No change of hue possible. Burst signal is present at grid of burst amp. I will go through the power supply again to see what is going on. The sync trouble seems to be directly related to low voltage condition. This is one weird color section!!! Very good b/w pic, though.
Kevin G.