12LP4 vs. 12QP4

[Eric H]

Does anyone have the specs on these two tubes or know why the sub book says they wont swap?

I know the LP4 has extra pins on the base.

[Steve K]

Eric:

The physical dimensions of those two tubes are slightly different. They have different anode connections and QP4 uses a single ion trap where the LP4 uses a double ion trap. Also, deflection angle is a bit different as well as some of the grid voltage requirements. I can send you the details of both tubes if you'd like.

Steve

[wiseguy]

12lp4---tube length 18 3/4
12qp4--tube length 17 1/2
12lp4 anode to coating capacitance is 750-3000 uuf
12qp4 has none..(must mean it has no coating)
12lp4 deflection angle is 54 deg
12qp4 deflection angle is 55 deg
electron gun specs are the same except 12qp4 uses single ion trap and 12lp4 uses double ion trap.
you could rewire the socket to get it to work but because of the differences in deflection angles you may not get yoke to fit properly...try it and see how it works..
terry

[Eric H]

THanks guys, sorry I've been slow to respond but I have been in bed with the Flu for the last couple days

well I can't imagine one degree of deflection making any difference, the QP4 did have Dag on it but it has all fallen off. The extra inch & 1/4 might make it stick out the back,

I thought it might have electronic focus or something but the Hoffman I want to use it in has a focus coil around the neck.

I guess I'll have to wait till I have the chassis working and see if I can get it to light.

Eric

[Eric H]

OK, I get the bonehead award for the week

All I had to do was look at the Schematic for the set.

It shows this chassis using a 12QP4, 12LP4 or a 10BP4, with the same base diagram for all.

[wiseguy]

i have 2 books on crt data.. but i never looked at the base wiring myself,but the specs on both electron guns are about the same... it should work..send us pictures!!
terry