17GP4 vs 17TP4
 

My family has a 1951 RCA console with a very dim 17GP4. I am planning to restore this set in the future, and there is a NOS 17TP4 on ebay. They are both glass/metal CRTs

Will these interchange?

Thanks!

Looking at an old GE tube manual, the tubes appear to be identical *EXCEPT* for focus voltage (pin6). The nominal focus voltage for the GP4 appears to be 2800 volts (5000 max), while the nominal focus voltage for the TP4 is 126 volts (500 max), some rewiring of pin 6 would be necessary.

jr

2800 volts to focus a B&W tube? sounds a little strange.

Edit, Ok, I see the specs but I can't recall ever seeing voltage like that on a B&W set?
Maybe I'm just used to magnetically focused sets.

Strange indeed, but I just found a schematic of a set using a 17GP4 (RCA Model17T155) in Sams 158-11, (1952). Pin 6 is "do not measure" and is connected to a 1V2 focus rectifier!

jr

Hmmm OK, maybe I'll wait for the right CRT then.

Thanks for the quick help and response.

The 17GP4 CRT is not all that common!
Also, RCA metal CRT sets are hard to convert to glass CRT's. The 17TP4 seems like a good alternative for the 17GP4. First thing, I would do is remove the 1V2 tube, so no mistake could be made. High focus voltage could easily damage a low volt focus CRT. Cut the lead to #6 terminal on the CRT socket and try it on chassis ground. Focus will probably be good. :yes:

Agree 100%... Many sets with LV focus offer a selection of "taps" to connect to pin 6, something like ground, 150v and 300v, depending upon what supply voltages are available in the set. It is *not* very critical. I have also seen tubes that just have a strap at the base which connects pin 6 to pin 10 (G2).

jr

Uh-oh.... bid war on the tp4???

im on the fence... :dunno:

SR

The 17GP4 was an RCA attempt to get around using a focus coil or magnet for focusing in 1951, supposedly due to some 'shortage" in magnetic materials available at the time or such. It was ONLY used for one year, 1951, and I am not sure any other tube numbers were used either. A set with that HV focus setup, like a color set has, is a RARE find indeed. I have ONE--and had to look long and hard for it. The 1V focus rect, often found in early color sets--looks VERY unusual in a BW set !!

My set is a 1951 so that makes sense. Since the set is unrestored I am still not sure the faint picture is due to old caps or a weak CRT

Probably a little bit of both.
You have to determine if the CRT is original to the set, or a replacement.
I only saw one set, with that CRT and never having to replace one, I don't know if that CRT was offered as a rebuilt, by one of the smaller rebuilders.
BTW, the only other high focus voltage CRT, is the 7GP4, as used in the 621TS. I was surprised to discover that fact. :scratch2:

Actually the 621 uses a 7DP4, the 7GP4 was used in the Philco 48-700 I think and is an electrostatically deflected tube.

A quick scan of my mid-50s GE tube manual shows the following with magnetic deflection and HV electrostatic focus:
7cp4, 7dp4, 9ap4, 10dp4, 10sp4, 14gp4, 17fp4, 17gp4, 20fp4, 20gp4, 20gp4, 21dp4.
I did not include Color or projection CRTs.

jr

The big question is, anyone gonna take a shot at getting this tube? Im still on the fence about my motorola, and will step aside if someone else has their heart set on it, but i might attempt it if no ones interested..

SR

I dawned on me, after the posting, about the wrong type number. :scratch2: