Hey Lee

Does the radio work well?

Steve

The Radio works quite well, AM and FM. I'm pleased with the performance.

I listen to it in the morning as I get ready for the day.

OK, here's the latest:

I installed the NOS 12QP4. I can only get a good level of brightness with the Focus Coil as far forward as the slots can go. Maybe I can get it brighter, but, the stops won't allow me to go further.

I'm using a single magnet Ion Trap, a Philco. It seems to work ok.

I have the Focus Control all the way clockwise, and I can't get a sharp focus on the screen.

Deflection is ok.

What now?

Try flipping the ion trap over and try again. It will now adjust with the magnet a half a turn from where it worked before. It may be that the magnet on the ion trap is not strong enough. In a case like this it helps to have an assortment of ion traps to try.

Try reversing the polarity on the focus coil (or flip it front to back if possible) that will change the range of focus, usually for the worst but with a different CRT it might be better.

I don't believe I'm getting peak brightness with the Ion Trap (it's the best performing of the bunch I have) because when I attempt to adjust Screen Voltage (R39 Control in Riders) with the Brightness Control (R118) set to 30-35V I can't get any illumination at all out of the CRT.

Still have the Focus problem as well. The Test Pattern squares up nice.

I can't physically flip the focus coil due to wiring constraints. They have to point rearward.

I'm wondering whether there is a way to extend the Focus Control at it's extremes, or whether reversing the wiring at the control would help.

I reversed the wiring at the Focus Control. No go, still have the problem, only it exists, of course, full counter-clockwise.

The Focus Control is 10Kohms, 4 Watts. Would a wider range control work, or can I extend the range with a couple of WW resistors? If I can, what value would I put in?

I'm guessing your focus problem is due to having the coil adjusted so far up the neck, you might be able to give it some more range by changing the resistors but it's possible it is so far off physically that it won't help.
It might also be detrimental to the CRT if the Ion trap isn't in the optimal position.

I know it's not much help, but what you probably really need is a 12KP4 tube, Aluminized, no trap needed (assuming it wasn't rebuilt with a bent gun) and a short neck like the original JP4.

Possibly a 12LP4 might work better also, I believe it has a longer neck than the QP4 so more room for the trap.

Perhaps you could find someone with one to trade for your QP4?

Tacked on a 7500 ohm 10W ww resistor onto the Focus Control to extend it, and I finally got a sharp focus with a little extra range to spare.

I set the Ion Magnet and Picture Tube Screen Control for the 12QP4 to the best setting possible. It looks mucho better than the dying 12JP4 that it came with. Decent brightness and contrast, and no ion burn to stare at, so I'm happy with it. Sounds good, playing thru an old DuMont 5" driver. I just sent the stock 7.5" loudspeaker out to be rebuilt.

I have it playing side by side with the Admiral 24A12, and the Admiral has better brightness and contrast. Of course, it's sporting a 10FP4 with strong emissions.

As far as the Ion Trap Magnet, I'm thinking I might come across one that is narrower so it fits closer to the focus coil and yields more brightness. I think I'm close to optimal right now.

If anybody has a single large magnet Ion Trap that is narrower than normal, I'd be grateful if they PM'd me.

Thanks

An ion trap with a stronger magnet might adjust closer to the base of the CRT giving you the needed extra room. Have you yet tried flipping the ion trap over and then adjusting it half a turn from where you have it now?

Yeah, I've tried all that, Tom. I've been through my small collection of Ion Traps, and I need a stronger single magnet type. I don't like the idea of running the CRT below peak brightness.

Anybody have a strong single magnet Ion Trap? Something that will couple closer to the Focus Coil?

OK. I removed the round black cardboard cap off the rear of the Deflection Coil, which gained me an extra 1/16" of exposed CRT tail. Repositioning the Ion Trap gave me a good gain of brightness. I think I'm in the sweet spot now, or real close to it.

I put some electrical tape around the Focus Coil where the metal contacts the Deflection Coil, just to keep things isolated. Works fine, and all appears factory, aside from the missing cap. I can live with that.

I think this 12QP4 might have been on the short side, or the guns were located a bit forward than specs.

Final Assembly of this set was interesting. After getting the chassis operational I figured F.A. would be anticlimactic. What I didn't realize is that manufacturing tolerances sometimes doesn't allow everything to just fall in place.

Alterations must sometimes be made. It's not like I could just grab another new CRT off the shelf...

I went back into the Andrea again, as it had an intermittant loss of HV due to a loose 5U4 socket. Fixed that, swapped out 5U4s until I got a bump in HV past 9K. It was at 8.5K.

I replaced all the remaining electrolytics, and picture quality improved quite a bit, with a fairly deep picture.

I also just received my rebuilt 7.5" cone speaker, and it sounds marvelous.

Going to keep the chassis playing on the bench for a couple of days before I load it back into the cabinet.

Incidently, what is the output of the HV Anode supposed to be for this set? I can't find a spec for it anywhere...

Hello Lee ,
Man you sure allows do a beautiful job on your Sets Are you Sure you are not related to Steve Jobs he was profectionist also .
I know you put lot time and work into your sets

RE HV IIRC 9KV

Thanks.

Yup. Mine reads 9KV. I thought it should be over 10K because it's feeding a 12" CRT, but i guess not.

I wonder what I can do for a mod to the HV section to boost it past 10K. I think I could get a better picture that way.

Anyways, she's on the bench, running fine. Will keep it there for a few days longer.

OK, She's done. Done done...

I found a large, single magnet Ion Trap that works fine, with the Focus Coil cardboard end cap installed. Picture is as bright and clear as I can make it. Probably pulling about 3.3 megs bandwidth. Not a bad picture.


Curly's back On The Air. Situation Normal.


All back together. I think it's finished.