Focus Coil circuits?

[Yamamaya42]

Originally Posted by MadMan

...Won't you also have to disable the existing electrostatic focus circuitry?

not necessarily, it does not seem to be that high voltage, and it's going to a pin that is not there, so it is not likely to hurt anything.

[mbates14]

Originally Posted by Kevin Kuehn

Have you tried the tube? Quite possibly it will focus just fine with no focus magnet or focus voltage. If you read the typical operational conditions there's a note C that specifies the preferred condition for best focus.

No I need to restore the set first. I just wanted to secure a CRT before i even tried becuase there would be no point. the original CRT was an open cathode. I tried to weld it but i was tapping too hard on the CRT and necked it.

[mbates14]

Here are some pics of the set I am working on.

[Electronic M]

Originally Posted by mbates14

Here are some pics of the set I am working on.

We're these pictures before you necked it?... because besides the bakelite base being off (a fairly trivial fix I can explain in a paragraph) it looks okay.

[mbates14]

Originally Posted by Electronic M

We're these pictures before you necked it?... because besides the bakelite base being off (a fairly trivial fix I can explain in a paragraph) it looks okay.

Yep. I took the base off on purpose because it was loose, I did this to determine if it was a broken wire causing no emissions.

But it was not. I let it cook for an hour, with no emissions whatsoever, I tried to go through the H-K Short removal/cathode welding process and tap on the neck. I got nothing. I tried different angles of the CRT and eventually i cracked the neck and that was that.

[Yamamaya42]

After looking, and looking... and looking...

This could be the tube that is in that box.
https://frank.pocnet.net/sheets/127/1/17BP4.pdf

This is just a guess on sight alone, no way to know for sure, also it's doubtful that it is NOS at this point, could be used or rebuilt, how does it read on a emissions test?

[mbates14]

Well it is definitely the same brand tube that is in there. The electron gun shows no signs of wear either. No I have not tested it yet but that's actually a good idea...

[Yamamaya42]

The 17BP4 & 17HP4 are identical mechanically and size wise, but differ as is the biasing, as in the 17BP4 is an older version, other than that, no dif, but that SHOULD have been stated on the box that it is a 17B not a 17H...

But it's pretty certain you have a 17BP4 there and it will be a pain to rig a circuit for focus for it.

[Kevin Kuehn]

Originally Posted by Yamamaya42

The 17BP4 & 17HP4 are identical mechanically and size wise, but differ as is the biasing, as in the 17BP4 is an older version, other than that, no dif, but that SHOULD have been stated on the box that it is a 17B not a 17H...

But it's pretty certain you have a 17BP4 there and it will be a pain to rig a circuit for focus for it.

Are you by chance confusing biasing with basing? Both share the same standard 12 pin basing with the exception a 17HP4 normally should have a focus pin in location 6.

[bandersen]

I think every CRT from the 40s through the mid-50s used the same pinout. I might have a spare PM focus assembly if you do end up needing one.

[Yamamaya42]

Originally Posted by Kevin Kuehn

Are you by chance confusing biasing with basing? Both share the same standard 12 pin basing with the exception a 17HP4 normally should have a focus pin in location 6.

yeah, i got the words intermixed, :/

key being that 17HP4 has 12L and 17BP4 (which that tube seems to be) has 12D basing.

and if bandersen has a PM assembly that will work, then that's the best way to go, cause as mentioned, the one I have from the broken 21EP4B is too strong for this tube.