[GarySP]

Amen what Tim says about discharging numerous times. I got tagged good grabbing too close to the anode AFTER it had just been discharged. Like he said, "it wont kill anyone" but you don't want to ever do it again! Take care and BE HEALTHY! Gary

[MrFixr55]

*TV Man, +1 on your post. My 2nd job after graduating college was a 3rd party bio-med repair service. We had some extremely interesting characters, some with rather interesting personality disorders. I was in the shop, carrying a cardiac monitor (essentially an o-scope with a high persistence CRT, sensitive vertical circuit and real slow horizontal circuit. This was about 42 years ago before computers, flat screens, etc.) One of our pranksters snuck up behind me and discharged a cap across my back. Needless to say, the cardiac monitor hit the ground and, needless to say, the CRT, along with a bunch of other stuff broke. He was forced to fix it on his own time. Fortunately, the busted CRT was confined to the monitor.

I

[Brian joy]

Hey guys have a few leeds on a replacement CRT but being asked on one if the 21EP4 is curved horizontally and flat vertically.....how can I tell from the literature I have along with my existing CRT?

Thanks

[Arran]

The picture tube in the first picture looks like it's spherical faced, which is common with rectangular picture tubes from the mid 50s onward. What you are thinking of are cylindrical faced picture tubes, some of the most common TVs featuring those are Sony Trinitron sets. However the number you gave, 21EP4, according to my G.E tube manual, are you sure that is correct?

[Brian joy]

Arran
I hope its correct as the existing crt has no model information on it. Another user Mr Fixxit had provided the model info from my earlier post. I have tried looking through the Sams paperwork to fully confirm but cannot see a definitive answer. My 52-T2142 Philco has no other information on it for me to tell so im kind of going by you all to lead me to the correct part. I too agree from looking at it that its more spherical than flat which you're 100% correct is what most of my 50s televisions have. Question i have is IS there a way for me to know fully that this is correct?  I have found a good used CRT that im awaiting pricing on as we speak. 

Thanks again

[TV MAN]

I agree with Aaron, it looks spherical to me. About the only ones I have seen that are flat vertically are the 17HP4 type, oft used in Zenith sets in the early -mid 50's. Similar to a Trinitron as mentioned. I had to hunt down one of those tubes- a TV I got off a widows auction when I was in college. Lost vertical sweep and had a bright line across the screen. Burned it. Looked for that tube for close to 30 years. I knew that TV since I was a youth. Anyway, end of my story

[MrFixr55]

Hi Brian,
"Curved horizontally but flat vertically" describes a CRT with a "cylindrical" viewing surface. If you look at the "mask" (the trim piece that surrounds the face of the CRT)
The DuMont that almost blinded me was meant to have a "cylindrical" Tube. A "spherical" tube will fit the mount but will not line up fully with the mask if the mask was meant for a cylindrical tube, and visa versa.

The schematics that Terry "RadioRoslyn posted for your set lists the CRT as a 21EP4A. According to my RCA Receiving Tube Manual, version RC24, a 21EP4A is a cylindrical face CRT, magnetically focused, with 70 degree deflection angle and with base diagram 12N. However, I kind of agree with the others that your tube looks to be spherical in the picture, but it is not always easy to tell. Per my RCA Receiving Tube Manual, 21WP4 and 21ZP4 are spherical face 70 degree tubes with magnetic deflection and focus, and base diagram 12N.

One other thing to check, since your current tube is a name brand (GE) and not an off brand, is that the tube number may be stenciled on the neck of the tube, similar to the way it is done on a regular tube. Using a flashlight in a darkened room, look for the number on the neck area of the tube. Be careful wiping the area as you may wipe off the numbers.

Good luck.

[Brian joy]

Thank you both. I will look at the neck today to check for any numbers. Appreciate all the help guys!

[GarySP]

Hi Brian. In looking a little further in that website I gave you I noticed there was a pdf of Cisin's Tube Substitution Guide for 1959. Your tube is located in Group 28. In your photograph I can't tell for sure but it appears spherical with an external tube coating. If that's the case then your tube could be a 21EP4A or 21EP4B. When you check the neck for any markings, also check the broken base... it might have been printed there. Take care and BE HEALTHY! Gary

[Brian joy]

Thanks Gary. I will check before continuing on to see if there are in fact any markings that will lead to a replacement.

[Brian joy]

Hey guys sorry took me all day to finally get back to the set and found a GE number 20DP4 on the tail connector. How far off tube wise is what we've been discussing as the 21EP4? 

Thanks

   

[GarySP]

Slight, but different tube dimensions that would require mounting modifications. The same CRT site also has a 20dp4 - used available. The Sams schematics are a help, but are vague in some respects. In fairness, the schematic showing a 21EP4 did not include this model. Time to talk to them again, I would consider. Take care and BE HEALTHY! Gary

[Radioroslyn]

Check post 14.  [Image: https://philcoradio.com/phorum/images/sm...humbup.gif]

[MrFixr55]

Hi Brian, 

It seems that this CRT may be a little rare.  20" units were not as popular as 21" Units.

The following is from the Cisin's Tube Sub Guide from Early Television Foundation.  Theoretically, everything in this group 25 that matches all parameters (including those not listed) is a fit.

The problem is this:

• 21EP4 is not in this group.  
  
• A 21EP4 has a cylindrical faceplate.  The surround (mask) will not fit.  
  
• Electrically, anything with Base Diagram 12N is the same wiring, but electric similarity is not guaranteed. 
  
• The dimensions of the faceplate in a 21EP4 are going to be bigger by 5/8" vertically by 2" horizontally.  This will require modification of the mounting.
  

• Per the Cisin's manual, the 20DP4 has a spherical faceplate. A 21WP4 has the same base diagram and dimensions at the faceplate but the tube is 1/2" longer.  In addition, although it is in the same group, it does not show as being a direct swap.  And the fact that yours is listed as a 20" but the 21WP4 should be a little bigger makes me wonder if it is a misprint.
  

• ETF has a 21ZP4, used. This has the same dimensions as the 21EP4 (bigger by 5/8" vertically by 2" horizontally than the 20DP4) but has the cylindrical faceplate. the Base Diagram of 12D indicates that it does not have an external Aquadag coating, but this can be applied.
  

Do yiy collect TVs?  Do you have another TV with a somewhat similar tube (55-90 deg, magnetic deflection, magnetic focus)?  You can extend the wiring from the Philco and connect 2nd Anode, Electron Gun, Yoke and Focus coil (and Ion trap as needed).  The purpose of doing this is to test the rest of the set so you know, that in addition to the work and expense of replacing the CRT, what else you are up against.

Keep the info coming, and good luck!!

[Brian joy]

Ok so spoke to Steve over at early tv and hes checking on the 20dp4. I do have another crt i believe is good. I will try and extend the anode and wiring connection to see if I have any response. Aside from the expense is actually finding someone here on long island willing to take a look. Been searching for a group to find a mentor on walking me through possibly with the set itself.  Few things I dont want to do is 1 damage anything further and 2 start in the wrong spot. So I know for sure the CRT I have is no good. So first obtaining one I will do. If anyone does know of someone willing to help bring another newbie into the fold and begin to learn proper testing and repair please let me know. Thanks guys.