#1
|
||||
|
||||
Substitute 12KP4 for a 12LP4
I recently picked up this 12KP4. It tests very good on my Sencore CR70 - plenty of emission and grid control. However, when I popped it into a worked set in place of it's 12LP4, I'm getting nothing
The specs look nearly identical on paper. The filament is glowing and I have ~10 KV at the anode. Maybe it's the lack of the DAG coating ? The previous owner removed it all to put the CRT on display. This set does have a doorknob cap on the HV so I figure it shouldn't make much difference. Also, the 12KP4 takes slightly more focus current, but that shouldn't matter much - should it ? Here are the specs: 12LP4 12KP4 Last edited by bandersen; 08-04-2010 at 07:59 PM. |
#2
|
||||
|
||||
As far as I can tell, a 12KP4 does not require an ion trap... might try it both ways however, as we have seen several tubes rebuilt with different guns than orig.
jr |
#3
|
||||
|
||||
It should work fine, the 12Kp4 is shorter and aluminum so it shouldn't need a trap.
The focus coil could be pulling the beam off center if it's too far out of adjustment but I would suspect the lack of Dag in this case, I had a set that wouldn't operate with an uncoated tube. |
#4
|
||||
|
||||
Quote:
|
#5
|
||||
|
||||
I thought it would be shorter too, but it's about the same length I covered about half the bell with some aluminum foil, made sure it was grounded and fired it up. No difference. Then I took a closer look at the gun. It sure looks like it's at an angle. I'll dig up a single and dual magnet and give it a try.
I don't see any signs of a rebuild. I also don't see any part#. I'm just going my the seller's word that it's really a 12KP4. All it says on the base is "CBS Palomar". On the other hand it is an aluminized 12" CRT. Last edited by bandersen; 08-04-2010 at 11:03 PM. |
Audiokarma |
#6
|
||||
|
||||
That did it Of course it needs adjusting, but it's not destined to be used in this chassis. I tried both a single and dual ion trap. The results were pretty much the same.
Does that mean that I should go with just a single I have plenty to choose from Last edited by bandersen; 08-05-2010 at 01:41 AM. |
#7
|
||||
|
||||
#8
|
|||
|
|||
It could easily be a 12lp4. CBS Palomar was their rebuilt tube line in the late 50's and early 60's. I wouldn't be surprised if it took a single magnet ion trap. Sellers seem to think that if the tube is aluminized that it automatically is a 12kp4. It probably came with an instruction sheet to use a single magnet ion trap.
|
#9
|
||||
|
||||
Thanks for the info guys. Yep, it's a rebuild. I pulled the CRT, felt along the neck and found a seam about 5" from the base. They did a good job - you can just barley see the seam.
|
|
|