Subbing 3AQP1 for 3KP4 with adapter?

[Phil Nelson]

I'm still seeking a 3KP1 to sub for the 3KP4 in my Pilot TV-37 during restoration. Meanwhile, I looked up some info on a couple of old working oscilloscopes sitting around the workshop.

One of them is an RCA WO-33A with a 3AQP1 CRT. Staring at both schematics, it looks like you could wire up an adapter to use the 3AQP1 in place of 3KP4.

What I'm missing is technical specs to tell me whether this would be practical, or just result in a Bad Thing, like burning up a perfectly good scope CRT or getting no raster.

Any opinions?

For what it's worth, you can find the WO-33A schematic at http://bama.edebris.com/manuals/rca/wo33a/ .

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[Eric H]

Phil, are you worried about breaking the tube or burning it out?

I was more worried about the latter given the history of that tube and the fact that mine would flare up badly when turned on so I wired in a 6.3v filament transformer.

I forget the part number but it's common and very small, I mounted it using existing chassis holes.

[Phil Nelson]

Thanks, I read about that in a previous thread and ordered an F-13X transformer when I ordered other parts yesterday.

I want to be very careful when powering this one up. The previous owner replaced about half of the caps (apparently in the 1960s) and made detailed notes of his work. He did a very tidy job, by the way.

The notes also include two drawings -- physical and schematic -- of the filament strings. I don't know whether he was rewiring for some reason, planning to make some change, or just wanting to learn more about how the set worked. I plan to trace all that stuff before powerup to make sure it's kosher, but just in case I miss some weirdness, I'd rather burn up a cheap green tube :-)

Phil Nelson

[cbenham]

[QUOTE=Eric H;2127934] "I was more worried about <--> the fact that mine would flare up badly when turned on so I wired in a 6.3v filament transformer."

I've discussed the 3KP4 'flare up' with another AK member who said the fil. transformer didn't seem to make any difference and the tube still flared at startup.
We wondered if wiring a 'globar' resistor in series with the fil. work OK? This type of resistor starts cold at ~100 ohms and drops to ~0.5 ohms hot.

A 3AQP1 should produce a picture but it may not fill the screen because it is just over two inches shorter than the 3KP4, and it's deflection plate sensitivities are different.

Best,
Cliff

[Phil Nelson]

I had thought of adding a thermistor, as well.

Or maybe just bringing it up on a variac. Wouldn't that eliminate powerup surge?

The 3AQP1 doesn't sound like it's worth the hassle.

Phil Nelson

[cbenham]

A variac would work fine for this application although it will be hard to hide it
inside the TV-37. #;^)

If using a 3AQP1 is the difference between having a tube in the set and not,
I'd try it to see how well it works.

Best Luck.

P.S.--
I have an Admiral 17T1 7 inch set with a GREEN 7JP1 in it. It had no tube when I got it so I took the tube out of a very old and extremely distressed RCA 7 inch O'scope.

[kbmuri]

For testing, a 7JP1 will work in your Pilot, no adaptor needed. Obviously it won't physically fit in the cabinet, but on the bench it should work fine. As mentioned above, they're still a cheap-n-easy find in old o'scopes.

[Phil Nelson]

Thanks. I have a line on a 3WP1, which also looks like it might sub.

http://www.mif.pg.gda.pl/homepages/f...041/3/3WP1.pdf

In rummaging around the shop, I found a 5BP1. (Don't ask me where I got it -- maybe at a garage sale Free box.) The only data sheet I could find is in French, but it looks like a possibility. It wouldn't fit in the set, but it could lie backward on the bench for testing.

I finished recapping and brought it up on a variac for the first time. No smoke, all tubes light, and there is sound of a sort. No raster, though. Time to start checking resistors and voltages.

Regards,

Phil

[kbmuri]

5BP1 has heater and cathode connected internally. Might be an issue. You would have to connect your Pilot's cathode circuitry to your heater string when it might not be connected (externally). Without a schematic I couldn't advise further.

http://www.bunkerofdoom.com/tubes/sy...s/5BNP16_2.jpg

[kbmuri]

Looks like I was wrong about the 7JP1 working without an adaptor. I saw a Pilot running a 7JP4 once and was told it was plug-n-play. I should'a checked the data sheets first though -- looks like not. Sorry for the misinfo. -k

[Phil Nelson]

Yes, I looked again at data for the 5BP1 and it would not work. Back to the junk box with it!

Phil