Rebuilding the VT-71 (TS-4H) - Videokarma.org TV - Video

miniman82 · #1 08-20-2010, 01:10 AM

This is the one I got for $30 at an estate sale a little bit ago. Barring some catastrophic chassis failure, the grand total to go from non-working heap to fully functional restored set shouldn't be more than $200 including purchase price. 30 for the set, 45 for the mask, 20 for the Amperite ballast, 15 for a picture tube socket, and 100 in capacitors. I'll refinish the cabinet with stuff my Dad already has in the basement, so that's a freebee. Budget build, if I do say so myself.

So far I have all the paper caps swapped out, rectifiers replaced, and new ballast installed. Still need to restuff the 'lytics and put the socket on the picture tube, more updates as they become available.

bandersen · #2 08-20-2010, 03:06 PM

Nice job

I see you didn't cut any corners - orange drops throughout. Good luck with the rest.

miniman82 · #3 08-20-2010, 03:12 PM

Orange drops are cheap when you buy them in bulk, I keep a stash of them at all times since I'm always working on tube gear.

mbates14 · #4 08-21-2010, 01:39 PM

Hey, where do you get the ballast tube at? i have a VT-71 from long ago, that is now unusable because of a failed ballast tube.

miniman82 · #5 08-21-2010, 06:58 PM

I got mine from the same guy Banderson did: http://cgi.ebay.com/AMPERITE-BALLAST...Electronics_R2

mbates14 · #6 08-21-2010, 09:19 PM

Thanks. I just bought one, at least now i know they could have been found. hehe.

The old one, the mica was falling apart and one of the resistor wires burned open, i tried twisting it together, but it only made a few tube filaments run hotter and burned out the vert osc tube.

bandersen · #7 08-21-2010, 10:37 PM

I'm glad that seller still has some left. Remember that you guys made need to move one wire on the ballast tube socket if your chassis revision wasn't designed for the 17A485459.

miniman82 · #8 08-21-2010, 10:56 PM

I already moved mine from pin 5 to 6, as per your thread. Thanks for figuring all that out, BTW.

mbates14 · #9 08-22-2010, 10:39 AM

How do you tell which one you have and when to move the pin? The metal shroud that went to my ballast tube is long since gone.

miniman82 · #10 08-22-2010, 12:03 PM

http://www.videokarma.org/showthread.php?p=2908131

miniman82 · #11 08-29-2010, 04:40 AM

Update: IT'S ALIIIIIIVE!!!!

Restuffed the last few caps, finished putting the CRT socket on (I'll never do that again), crossed my fingers and flipped the switch....

.......

Nothing, at first.

Figured HV might be down, so I pulled the cover off. I saw the 1B3 filament glowing dimly, so I knew the oscilator was running. Tried moving around the feedback spring to different positions, but still nothing. Then I tried the brightness control- Bingo! It was just down too far, now I had a scrambled line on the screen.

Vertical was not working at first, which was caused by dirty 12SN7 pins. Cleaned out the socket, and I now had a full raster. Then horizontal wouldn't lock worth a crap, and I discovered a capacitor on the hold control was the wrong value. Put the right one in, and the oscilator started running at the correct frequency. Now I have a decent picture and clear sound on channel 3, coming from the cable box. Can't believe this thing didn't have any dead tubes...even the 7JP4 has pretty good brightness.

Next I need to do the retrace blanking mod to get rid of the lines, and next weekend it's looking like I'm headed to Beloit, so I'll bring the cabinet with me to start the woodwork. All in all, this is turning out to be a fun and cheap TV to get going. Not only that, I think it'll have a superb picture when I'm done with it. I think I'll be putting in a cooling fan though, this chassis puts out a fair amount of heat.

Enjoy the pics!

mbates14 · #12 08-29-2010, 01:42 PM

Awsome!!! I love to see these sets play.

mine works good too, but i have a dark bar at the extreme left of the screen, along with whats believed to be some barkhausen noise.

bandersen · #13 08-29-2010, 03:03 PM

Congrats

That picture looks great

pugs5061 · #14 08-29-2010, 03:34 PM

Congratulations! I'm at almost to the same spot with my 9VT1 but still haven't got a raster

. I'm thinking my 8bp4 is bad but I'm not giving up yet! I also am wondering if my ballast tube could of came with a bad filament (same source as yours). I tried this morning and the horizontal is trying(you can hear the high pitch, and it changes as you turn the adjustment), no sound but I can't find channel 3 thus possibly no input and it may be my fault. Off to keep playing!
My understanding is that both the 7JP4 and 8BP4 are very difficult to test. I haven't attempted with my B&K 400, I don't have the correct tube socket adapter but can the Sencore units like Bandersen has do a decent job testing them? I think a while back he offered to help me test this CRT. Unfortunately finding time to do this is a ways off! Work, Sons Football, Daughters Softball, Wife working, etc., etc. LOL.
Congratulations Again, Its nice to know there at least a few of these old Moto's going within 50 miles of their headquaters!

bandersen · #15 08-29-2010, 04:03 PM

Here's the pinout for that ballast tube. You can test it with an ohmmeter. The Sencore CR70 lists settings for the 7JP4 in the manual so it definitely supports it. You can even see the screen glow a bit while testing it.

Of course, you can also test one by popping it into a working set. That's quite easy to do by disconnecting the CRT socket and flipping it over to connect to the test CRT outside of the cabinet.

Ballast# 17A485459

A = 37 ohms
B = 132 ohms
C = 200 ohms
D = 111 ohms