My Motorola VT-73 Arrived! - Page 2 - Videokarma.org TV - Video

zenith2134 · #16 10-10-2009, 11:44 AM

Congrats on a very neat set.

These type of tv's are kind of exotic for me, I don't think I've ever seen one like it. Would be quite the adventure to restore one.

bandersen · #17 10-10-2009, 05:40 PM

Kudos on getting it running and sorry it was short lived

Those old metal ballast tubes are prone to burn out. Did you get a glass ballast tube? They are much more reliable and provide a regulation effect when the set powers up.

7"estatdef · #18 10-10-2009, 05:47 PM

I put a pair 1N5408's with no resistors in mine and had no problems with the HV. But it has developed a slow vertical roll after 10 or 15 minutes. Very annoying!
Terry

bandersen · #19 10-10-2009, 06:09 PM

I used 1N4007 in 3 of my sets without resistors. All of them work fine and B+/B++ are right on.

That being said, it is generally a good idea to use a dropping resistor and will cut the current through the ballast a bit.

leadlike · #20 10-10-2009, 06:31 PM

I used 1n4006 diodes. I was all out of the '07s, but I should think the ones I used are close enough.

The ballast I have is one of the crummy old metal cage ones. I opened it up, and the wire is strung over mica sheets, where it is periodically tacked down to the mica with blobs of ceramic cement. Well, age and transport have knocked those glued down portions free, so the wire was just getting shaken quite a bit, which probably also weakened things.

leadlike · #21 10-10-2009, 07:35 PM

Some screen shots. Sorry about the lack of focus, that combined with the wrong shutter speed really doesn't do the 7GP4 justice.

[ATTACH]100_1834.jpg[/ATTACH]

bandersen · #22 10-10-2009, 07:46 PM

Nice

MST3K with Joel

leadlike · #23 10-11-2009, 05:46 AM

Okay, I have it running again! I built ballast with Dale 25W resistors per Phil Nelson's site, and that did the trick. I'll probably get a more stock-looking glass ballast at some point.

I started replacing resistors in the vertical section, and while the shrinking problem has disappeared, the vertical hold is still very touchy. I hope to have this corrected before calling it a day with this one.

It is running so well that I even brought it into work to show off (it's the weekend, so we really haven't anything else to do) and it ran like crap of course. Between the server racks and the fluorescent lights, you could just make out the picture in a hail of static and herringbone. The set ran like it had a sound misalignment, too. I get it home and it runs fine as ever. I'm sure everyone at my job just thinks I'm more insane than ever, but what else is new?

Phil Nelson · #24 10-11-2009, 11:16 AM

Quote:

Originally Posted by leadlike

hail of static and herringbone

I imagine many 1940s TVs would have the same response there. They were designed to be sensitive enough to receive weak stations. The RF environment they lived in was a lot cleaner than many places you'll find today.

Re the old ballast going poof, it's not unusual for marginal components to give up the ghost when they get the right voltage for the first time in decades. If you try the set regularly while you're replacing things, you can notice gradual improvements -- and sometimes new problems. The problems were there all along, you just didn't notice them while distracted by bigger issues.

These Motorolas are lots of fun. Enjoy!

Phil

7"estatdef · #25 10-11-2009, 01:10 PM

I have thought of for the fun of it hooking a 5 or 10H choke in place of that resistor in the ballast tube. Would probably jack-up the B+ a bit and make it a little cleaner. Seems pretty clean to start with (not much hum at all) Has any one got a copy of this? http://cgi.ebay.com/ORIGINAL-Motorol...item53dd4ae608
Looks Kewl? Nice table too!
Terry

leadlike · #26 10-13-2009, 02:33 PM

I've got the set pretty well dialed in now-I just have these interference lines scrolling across the screen. Can anyone speculate as to their source? This is a screenshot from a DVD player feeding the tv through an RF modulator. But even without the modulator signal, the set still has these lines:

100_1836.jpg

I'v worked through the resistors, and replaced about a dozen marginal ones, mostly in the vertical circuit. I've had it running for about two hours now, and it has not needed many adjustments, just a little fiddling with the vertical hold during warmup, and that was pretty much it. If this continues, I'll be pretty satisfied. Does anyone have a recommendation for a gasket replacement? I know there is a company that produces them, but they are sold out. I am more concerned with stabilizing the crt rather than aesthetics.

bandersen · #27 10-13-2009, 03:49 PM

Do you have the metal flyback, CRT and tube shields in place?

leadlike · #28 10-13-2009, 04:38 PM

All shields appear to be in place, in addition to the crt and flyback shields, I have these tubes shielded:

12sn7 clipper, AFC
6ag5 RF amp
6ag5 1st IF

I noticed that I can use the fine tuning to somewhat eliminate these lines, but that's all I've tried thus far.

old_coot88 · #29 10-13-2009, 05:34 PM

Quote:

Originally Posted by leadlike

I've got the set pretty well dialed in now-I just have these interference lines scrolling across the screen. Can anyone speculate as to their source? This is a screenshot from a DVD player feeding the tv through an RF modulator. But even without the modulator signal, the set still has these lines:

Attachment 165155
Well, there's two sets of lines showing. Do you mean the white diagonal lines? That looks like vertical retrace. Do they go away if you turn down the brighness? Then there's dark bars slanting in the opposite direction. That looks like RF (from a computer power supply maybe?). Bill(oc)

leadlike · #30 10-13-2009, 07:03 PM

The white lines are vertical retraces, I don't think these suitcase sets have vertical blanking, so they are pretty apparent.