Hallicrafters T-506 scored

[bandersen]

I've noticed it mostly on late 40s knobs. It's not really a strong smell. I first noticed it when I opened a small box of knobs that had been sealed for many years.

I've been studying that 505 schematic and it does seem pretty close to my sets other than the 6SH7 tubes. Weird design. Especially the power supply and HV portions.

Here are links to a schematic I scanned from Most Often Needed Television Servicing Information 1948 edition.

http://www.bobandersen.com/images/ha...5%20sch-01.jpg
http://www.bobandersen.com/images/ha...5%20sch-02.jpg

Phil - any concern about the series wired 7JP4 filament?

[Phil Nelson]

Originally Posted by bandersen

concern about the series wired 7JP4 filament?

Some folks install a little filament transformer to supply the CRT and wire a power resistor to take its place in the filament string. I did that for one of my series sets (don't recall which, offhand). I bought a transformer for my Pilot TV-37 but haven't put it in yet. It is a Triad F-13X.

Phil

[bandersen]

Originally Posted by Phil Nelson

Some folks install a little filament transformer to supply the CRT and wire a power resistor to take its place in the filament string. I did that for one of my series sets (don't recall which, offhand). I bought a transformer for my Pilot TV-37 but haven't put it in yet. It is a Triad F-13X.

Phil

Thanks Phil.

Sounds like a good idea - there's plenty of room to add one in.

Can you explain that crazy power supply? A 25Z6, 6X5 and a selenium rectifier!

Did you replace it with silicon? If you did, any change to the18 ohm resister in series with it?

Thanks again
Bob

[Phil Nelson]

Yes, three rectifiers and seven electrolytics if I'm counting right. My National TV-7W has something similar, with a 25Z6 identified as a rectifier/voltage doubler and 6X5GT as a voltage tripler. Maybe something like that is going on here, although I haven't looked closely at either schematic.

A 6X5 rectifier is notorious in radio circles for developing a heater to cathode short. Various remedies are used, from installing a fuse to replacing it entirely. An Internet search may uncover some of those discussions. Perhaps the risk is negligible in a series string set, which has no power transformer to fry.

I'm a fan of the CL-90 ever since I put one in an RCA color set. Cheap and effective, just understand that it may get hot.

When I did my 505, I probably would have replaced the selenium rectifier with a 1N4007 diode and not changed anything else. Some people add more resistance in series with the new diode.

Phil