1948 (TS-4H) Motorola VT71 restored!

[Adam]

I'm surprised the picture is that clear with just a short wire off the modulator. What antenna is the moto using, is it still hooked to that "astro dog," or are you using something larger. And the 2nd doctor is my favorite, it's too bad they lost so many of his stories. I've got 4 of these motorolas sitting in the attic awaiting restoration.

[bandersen]

Originally Posted by Adam

I'm surprised the picture is that clear with just a short wire off the modulator. What antenna is the moto using, is it still hooked to that "astro dog," or are you using something larger. And the 2nd doctor is my favorite, it's too bad they lost so many of his stories. I've got 4 of these motorolas sitting in the attic awaiting restoration.

I switched to a proper set of rabbit ears. The astro dog is actually a pretty lousy antenna. I used a vertical wire about 12 inches long on the modulator.

Troughton is my fav too. I've been watching the whole series (recons included) from the very beginning. I'm up to Moonbase

[Gohan]

Good job! Looks very nice!

Gohan

[M3-SRT8]

That's good work, Banderson.

Your Troubleshooting Skills are better than mine...

LJB

[Sandy G]

I wish I knew how to work on TVs like that, but I'm too damn stupid to figure it out...I'm serious. I NEVER COULD make head nor tail out of basic electronic theory, & I've studied it, had people try to "splain" it to me, watched instructional videos...The whole 9 yards...It's like there's a 10' high wall there that can't be breached...Its like its worse than Chinese Algebra or some damn thing...I am in utter AWE over you wahoos who CAN & DO work on 'em, & can make 'em "shine" like that..My hat's off to you..But I'm still not 100% convinced that electronic theory, watts, volts, amps, capacitance, resistance, diodes, triodes, etc, all that stuff is a bunch of made-up hooey to keep us peasants in utter thrall, that Electronics really IS actually magic, & all youse byrds are really wizards 'n' warlocks, practising your arcane & black arts...

[bandersen]

Originally Posted by Sandy G

I wish I knew how to work on TVs like that, but I'm too damn stupid to figure it out...I'm serious. I NEVER COULD make head nor tail out of basic electronic theory, & I've studied it, had people try to "splain" it to me, watched instructional videos...The whole 9 yards...It's like there's a 10' high wall there that can't be breached...Its like its worse than Chinese Algebra or some damn thing...I am in utter AWE over you wahoos who CAN & DO work on 'em, & can make 'em "shine" like that..My hat's off to you..But I'm still not 100% convinced that electronic theory, watts, volts, amps, capacitance, resistance, diodes, triodes, etc, all that stuff is a bunch of made-up hooey to keep us peasants in utter thrall, that Electronics really IS actually magic, & all youse byrds are really wizards 'n' warlocks, practising your arcane & black arts...

I dunno about all that Although I do have a BSEE, I got all my practical knowledge from hanging around hamfests, forums like this and a whole lot of tinkering.

I think it just takes time to sink in. Hopefully, it will all make sense to you soon.

[zenithfan1]

I looked for modulators and found a few. Thanks, your post reminded me to keep looking for them. The last time I checked the bay a few months ago I found none and forgot about it.

[bandersen]

I had been using the crappy JFD metal ballast tube that came with this set, but no more!

I just scored some Amperite ballast tubes



These are glass enclosed balllast/regulator tubes filled with an inert gas. They really soak up the juice when the sets turned on and protect all those series wired tubes.

Technically, this tube is designed for the TS-18 chassis which specifies a 111 and 132 ohm element while this TS-4H calls for 105 ohm elements.

However, I've done the math and here's what I come up with. Yes, the 7JP4 draws 600ma and is in both strings.

    Series Filament #1                 Series Filament #2         
Tube    Type      V      A          Tube    Type     V      A
V-13    25L6      25    0.3         V-12    25L6     25    0.3
V-8     6SL7     6.3    0.3         V-6     6AU6    6.3    0.3
V-10    12SN7   12.6    0.3         V-12    6AG5    6.3    0.3
V-11    12SN7   12.6    0.3         V-17    12AT7   6.3    0.3
V-18    12SN7   12.6    0.3         V-2     6AG5    6.3    0.3
V-15    7JP4     6.3    0.3         V-3     6AG5    6.3    0.3
                75.4                V-4     6AG5    6.3    0.3
                                    V-5     6AU6    6.3    0.3
                                    V-16    6AL5    6.3    0.3
                                    V-15    7JP4    6.3    0.3
                                                   81.7

Assuming 117 VAC at the outlet, here's what I get which is not far off the TS-18 values.

(117 - 75.4) / 0.3 ~ 140 ohm
(117 - 81.7) / 0.3 ~ 120 ohm

That just leaves one issue - the pinout differs by one pin. I just needed to move the AC line from pin 5 to 6. No biggie.



Here it is in the set ready for testing.



Here's a crappy little video show it in action. One of these days I'll hook up my good digital video camera.

http://www.youtube.com/watch?v=HC86eiGhw_o

So, if you can find one, you shouldn't have any trouble using them in a VT71 set.

[zenithfan1]

Looking good! I can't wait until mine come! I hate the crappy metal ones.

[compucat]

I just ordered two of the glass ballasts from Ebay. When looking for these, search for amperite ballast tube. I still may make a resistive replacement as these are hard to find.

[bandersen]

Originally Posted by compucat

I just ordered two of the glass ballasts from Ebay. When looking for these, search for amperite ballast tube. I still may make a resistive replacement as these are hard to find.

They sure are hard to find and I have four sets that need one! I'd been researching technique to make resistive ones for weeks before coming across these and even ordered some resistors. So I make make up one or two as well.

[jeyurkon]

Weren't the original ones that you need the amperite 17A470303? Vacuumtubesinc has two of them.

John

[bandersen]

Originally Posted by jeyurkon

Weren't the original ones that you need the amperite 17A470303? Vacuumtubesinc has two of them.

John

Ah yes, so they do and almost twice what I paid for these

That's why I did the math to see if the '459 was a good substitute. According to my calculations (which have been confirmed by others), this tube is actually better. The two filament strings in the TS-4* chassis are not equal and 105 ohms is a bit too low when using modern line voltages anyway. I'd also noticed that my filaments were running a little hotter than they should.

Now, there a nice even glow with this ballast tube

That being said, I imagine the '303 Amperite glass tube is superior to the '303 JFD metal ballast tube. I'm curious if someone has used the '303 and has any thoughts on it?

[zenithfan1]

One of mine arrived with a broken element I hope I can get a replacement.

[bandersen]

Originally Posted by zenithfan1

One of mine arrived with a broken element I hope I can get a replacement.

Damn, that blows

Looks like he has a few left. I hope you can exchange it for a good one.

Bob