It's alive! Experimental Delco Car TV

[Bobby Dip]

I finally decided it was time to turn off the scope, and try a picture tube. I bought a 5AXP4 test tube on eBay. (To my great surprise, it's labeled "GM Delco" I worked at Delco Radio for 32 years, and never heard of Delco manufacturing any tubes of any sort. Back in the 50's, Delco rebadged a few TVs and sold them through United Motors. BUT, why would GM/Delco bother to rebadge a low volume test CRT ??????)

When I first tried the 5AXP4, there was nothing on the screen, no line, no dot, nothing. The HV, G2, G1, and cathode voltages checked OK. and there was video on the cathode. Then I noticed that the 5AXP4 data sheet said the tube is self focusing (electrostatic). I also noticed there was a magnetic ring on the yoke that was removable. So, I removed it and voila, there was a picture! I guess magnetic focusing and electrostatic focusing don't play together well.

I have yet to try out the 8AP4 that I bought for this set. (This set came out of the company vault with no picture tube, power supply, or documentation.)
Actually, the 8AP4 was just a guess. It will fit physically, but will it work? One thing that bothers me is that the 8AP4 has no G2, but the socket has 300V for the G2 pin. At least I know the set will work with some tube, now!









Bob D.