My DuMont RA-113 has a Sylvania 17BP4B in place of the original-issue 17AP4. Anyone know offhand if that CRT is aluminized?

Phil Nelson

My GE tube manual says that it is, and also shows that it uses a single magnet ion trap.
jr

Huh, I found a couple data sheets for that tube number online and the B version is aluminized. Both refer to the positioning of an ion trap, also. I'm not sure, but I had heard that you often didn't need an ion trap on an aluminized tube.

Thanks! Single magnet ion trap is what it has. I may try going bareback just to see what happens, but we're a long way from powering up at this stage.

Regards,

Phil Nelson

I may try going bareback just to see what happens, but we're a long way from powering up at this stage.


I dont think that you'd get any electrons on the screen if you go bareback. As the magnet will bend the electron beam to avoid the trap target. The ions are way more massive, and the magnet has little effect on them, and thus they hit the side wall of the electron gun. Or did they aim the ions at the getter patch on the neck glass?

Look at the CRT gun. If it is bent, or at an angle, it needs an ion trap. If it is straight, it does not use one. It will not work at all without it if it is needed.

Look at the CRT gun..... It will not work at all without it if it is needed.

You can believe it!

Does your RA-113 still have the back? If so, how does the 17BP4 fit? I have the original 17AP4 in my Tarrytown but the base had been knocked off and one of the wires broke off at the glass. I fixed it but I'm not sure how long it will hold up and have a 17BP4 to use as a spare. I think the 'BP4 is a little longer than the 'AP4.

My RA-113 with the 17BP4A, and original set back, comes out even to the back of the set, almost. I believe there is less than an inch clearance between the socket and the set back when it is buttoned up.

Mine has a big ion trap with DuMont part number on it.

The serviceman who replaced this tube cut a small hole in the back cover for the CRT socket. Otherwise, the back would have bumped the socket.

I started writing a little article about this set, although so far I've done nothing but take it apart.

http://antiqueradio.org/DuMontRA-113Television.htm

Phil

I like what you have written about your set. I was going to ask you about CRT removal, but you basically tell me what I need to know in your writings.

My set is the Burlingame in mahogany. My set doesent have all the heat markings all up the chassis from the HV cage like yours does. Hopefully, your filter electrolytics didnt short, and kill the 5U4, and burn up the power transformer, like mine did.

Take it easy around that skinny neck if you remove the CRT.

The HV cage looks ugly, but I think that's just corrosion from sitting unused in Seattle for decades. It's completely black on the bottom, where moisture would naturally collect. No sign of fireworks inside the cage or elsewhere. The rest of the chassis only has typical grime. The 5U4GB tested fine, as did all but one of the other tubes.

Jury's still out on the CRT. My tester says zero emission, but the filament has continuity, so I'm leaving it to cook on the tester overnight. I've seen one wake up after a slow cook, and if it's truly dead, there's nothing to lose.

I really shouldn't be spending time on this. Perhaps I'll make a capacitor order list and then put it aside. I need caps for the Westinghouse, too.

Phil Nelson

Jury's still out on the CRT. My tester says zero emission, but the filament has continuity, so I'm leaving it to cook on the tester overnight.
Should I see a filament glow? Nothing visibly lights up. I test 1.5 ohms between the filament pins.

Phil

http://antiqueradio.org/art/temp/CRT17BP4BNeck.jpg

1.5 ohms sounds correct... you should be seeing light, can you measure current from the heater supply? Does the neck feel warm? If the tube is very gassy the heater could be very dim, but it would likely burn out quickly.

jr

Forehead slap. In the course of reconnecting everything to measure current draw, I noticed that one of the tester control settings was incorrect.

Now there's a nice filament glow. Emission started at zero, but it's slowly creeping up after a few minutes. Maybe there's hope for this old girl, after all.

Thanks.

Phil

After sitting on the tester for a couple of days, the emission needle crept halfway up the scale, midway between Bad and Good.

I tried the Auto Restore function on my Sencore CR70 and now the emission tests well into the Good zone -- a definite improvement.

I hadn't tried that function before. Pretty fun. This CRT may be nearing the end of its days; it looks pretty weak on the Life test. It may be good enough to use during restoration, anyhow.

Phil