Assuming the heater amperage is the same I wonder if you could change some of those tubes for the higher voltage versions?
6CB6
6U8
6DT6
6J6
25DQ6 I think there was one of these?

Yes, there was 25DQ6. Good idea, but, unfortunately, those are all 300mA.

The hot chassis fix here is to rewire the switch to switch the power supply instead of the chassis. I have the fix in more detail on my website. You want the chassis wired directly to the interlock, and the switch to the power supply. Polarize the plug so the wide blade is to the chassis.

Because never, ever, is any AC outlet ever miswired....

No, pretty sure that is an aftermarket item.

Just checked, my Green one has a couple holes where an antenna may have been mounted, it also has some factory untapped holes that may have been for a factory antenna.

Thanks for the info. The anodized green set is really cool :yes:

Here's the original schematic and my proposed modifications to replace the seleniums and eliminate that 20W filament dropping resistor.

http://www.bobandersen.com/images/Ad...102/sch-01.jpg


I figure I can replace the 10 ohm fusistor with a plain fuse and 100-200 ohms to drop the voltage down when the seleniums are replaced with silicon.
Seems easier than using two separate resistors - one for each diode.

My hope is that the CL-90 will provide a soft start but not restrict the current too much. I have a CL80 and CL-130 I can experiment with too.
Perhaps I should use a diode that can handle more current ? The surge might be too much for a 1A 1N4007.
http://www.bobandersen.com/images/Ad...102/mod-01.jpg

The 1N4007 will be fine. Silicon diodes can take a brief surge higher than their average current rating. You'll have to look at the brightness of the heaters in the tubes to see if they look to be the right level, as a voltmeter won't give a meaningful number (though a true RMS meter might).

As for the hot chassis fix, relocate the switch to the filament circuit and your low voltage fuse. Connect the now empty lug on the interlock to the chassis. Polarize that side of the line cord, and hope your outlets are wired correctly. As noted earlier, these sets were notorious for hot cabinets.

I finished recapping the set over the weekend. I unmounted and restuffed all the eletrolytics and replaced all the paper caps with some nice Cornell Dubilier, Mallory and Orange Drops.

I uncrimped the ends on the two electroytics cans that are exposed.
The rest I just cut open because the seam will be covered by a cardboard tube.
http://farm6.static.flickr.com/5258/...9ffc5eeb_z.jpg http://farm6.static.flickr.com/5219/...b0571849_z.jpg http://farm6.static.flickr.com/5211/...34e2dffb_z.jpg

New caps installled
http://farm6.static.flickr.com/5252/...ed5e5874_b.jpg

I also cleaned things up a bit while I had it all exposed.
http://farm6.static.flickr.com/5096/...56d40506_b.jpg

I left the big 20W dropper and seleniums in place. I'll tackle those next.

The picture seems a litle crisper and the sound is much better :)
The horizontal hold is still very touchy though.

Perhaps I should replace the dual selenium AFC rectifier ? It's the green thingy on the circuit board in the picture above.
What type of modern diode would be appropriate ?

http://farm6.static.flickr.com/5057/...71177926_b.jpg

I tacked in a 1N4007 and CL-90. I also disconnected the CRT and stuck a 5 ohm resistor in it's place just in case I got something wrong.
I turned the set on and the filaments slowly lit up to the normal brightness :)
I reconnected the CRT and it works just fine. The CL-90 getts a little hot - maybe 2-3 watts. Certainly better than 20W :yes:

I also tried a CL-80 (slightly lower 'ON' resistance) but didn't notice much difference.

Now, on to the selenium rectifiers. I checked B+ with them still in the set and it's only 213 volts :no: It should be 255!
I'm really curious to see what effect getting B+ up to the proper level will have.

http://farm6.static.flickr.com/5055/...eda11499_z.jpg

Here are the final modifications I went with. I rewired the power switch as Big Dave suggested.
It runs cooler now and B+ is dead on.
http://farm6.static.flickr.com/5060/...94242629_b.jpg

I mounted the new components on a terminal strip near the AC interlock.
http://farm6.static.flickr.com/5218/...8eff2b09_b.jpg

Do you mean that the set as a whole runs cooler? Also, what do you think was keeping the B+ below specs and did bringing it up provide any noticable performance improvement?:scratch2:

Well at least one corner of it is cooler. That's where I've replaced the 20W filament dropper with a diode.

The old seleniums were keeping the voltage down. They got noticeably warm during operation. I suspect their resistance has increased over time.

As for performance - it's a mixed bag. I can get a brighter picture now, but the contrast isn't as good. Also the vertical retrace lines are more visible. The horizontal sync is still flaky like it has been since I first powered up the set. I suspect I need to replace the dual selenium AFC rectifier. The important thing is that i can stop worrying about the seleniums go up in smoke while I continue tweaking the set. I've had it happen once before and don't ever want to experience that again :yuck:

I'm also checking the resistors more thoroughly than I did first time around. I'm considering replacing the germanium video detector diode while I have the set open too.

I take it that the diode has a similar forward resistance as the old wire-wound resistor had in order to maintain the proper voltage. I am sort of new to the whole concept of replacing one component with a totally different, more modern component. I have read up a bit on eliminating 5U4s or other tube diodes used in a rectifier configuration, and replacing them with silicon diodes and a resistor to drop the same voltage as the tube filament. I have seen a few sets with the selenium rectifier disconnected and some older (germanium?) solid state diode(s) wired in its place. I thought that selenium rectifiers tended to run a bit hot, hence the cooling fins. I KNOW that they smell terrible when the finally do burn up, but the few that I have seen burn up were caused by bad electrolytics.

The silicon diodes have a lower resistance than the seleniums. That's why I have to increase the 10 ohm resistor to 22 ohms. I actually used a 32 and 75 in parallel each rated at something like 25 watts because that's all I had on hand. Really I think a 5-10 W would be fine.

As for using a diode in the filament string, that's a new concept to me as well. I first heard about it a while back as a potential replacement for the nasty VT71 ballast. I didn't actually try it until a few weeks ago in a Philco 37-611 radio. So cool that one little bitty device can replace a big 20W resistor and generate virtually no heat.

There is nothing wrong with the huge, original resistor and I could have left it alone. However, this little set uses around 130 watts and I figure any heat savings are a good idea.