Motorola VT-71
 

I've dug out my TS-4J and started working on it again. Short of a vertical problem I think it's working ok. Going to replace the vertical output tube socket with a ceramic one. I remember reading that it would be a good thing to run the 7JP4 filament off of it's own transformer rather than the string. Is there bad place to mount it 'cause of ac coupling? I thinking was of under the chaiss near the filter caps.
Terry

I picked up one of these TS-4Js a while ago that had been converted entirely to filament transformers. But the wiring of it was a bad mess, which I eventually sorted out, I got it to work with the transformers, but never that well, although I don't recall ac coupling being a problem. Here's a pic of where the transformers were mounted: http://www.audiokarma.org/forums/att...8&d=1134020896

I have since picked up 1 empty suitcase cabinet, and 2 other TS-4Js, both in cabinets that need work, 1 with a good 7JP4 and a complete original chassis, which I plan to restore and put in the suitcase cabinet. And 1 with a bright 7JP4 which arcs in the base, and is missing the flyback, but otherwise has an unmodified chassis, I was going to part out the chassis modified for filament transformers to restore this one, and put it in the already refinished cabinet the modified chassis came in. I also have that 7JP4 that originally came in that modifed set that me and jpdylon rejuvinated yesterday on his beltron, which I'll use in that set, if I can't fix the arcing in the other tube.

I was just planning on replacing the ballast tubes with resistors on both chassis, using that method I saw posted here before mounting them on a piece of metal atop the chassis. I would think you would have to add an extra dropping resistor to replace the 7JP4 in the filament string, have you figured out what value yet? If using a transformer for just the 7JP4 works well, I might try it on my sets when I get to restoring them.

I've got three myself two J's and I think B Only two good 7JP4's The transformer setup is to isolate the 7JP4 heater from heater string and ballast tube. If it burned out and shorted it could take out the crt.The other tubes are pretty common so I don't know if it's worth the work to rewire. As for the resistance I think it's mentioned in the Motorola service manual. It's used to operate/troubleshoot the chaiss without the crt. I'll take a look. I found a mod to fix vertical retrace. I'll post it later. I'll mention be very careful with your 7JP4. The defection plates have a nasty habbit of getting loose. I noticed on my set the picture moves a bit when I turn it up on it's side.

Gosh all we need now the mask!!!!
Terry

VT-71 & 73 Retrace lines fix
 

Found this post on another board and thought it may be helpful here.

http://antiqueradios.com/forums/viewtopic.php?t=12044

Terry

Adam, I bought a NOS rebuilt 7JP4 that arced inside the base (but outside the glass), you could actually see it by looking down through the back of the neck.
I was able to remove the base and repair it, one of the wires got bent over when it was originally installed causing it to arc.
I wouldn't wish the job on my worst enemy though, getting 12 wires back into the pins was a nightmare, terrified the whole time of breaking one off!
Anyway, just wanted to let you know there's hope for it.

A while back I picked up a 3" Heathkit HO-10 monitor scope. After using for a bit it devolped an intermitant and it turned to be the solder connections at the socket. Carefully removed the base and scraped all the copper wires til they were nice and clean. Solder on some long peices of thin wire like #36 to wires coming out of the crt. (3RP1) Used those to guide the base back on to is proper place. Solder it all back and has worked great ever since. The hard part is remembering which ones go where. Getting them in place wasn't bad at all.
Terry

I took a look in the manual for the resistor to subtitute in place of the 7JP4 heater. When serviceing the chaiss they just jumper across pin 1 & 12 (heater). If you want to service without HV they use a 75ohm 10w resister across the 25L6 HV osc heater or remove pins 3 and 4 ( plate and screen) from a spare 25L6.I think I was thinking of the 25L6 instead of the 7JP4.
Terry