Minty Motorola 9T1 restoration - Page 2 - Videokarma.org TV - Video

bandersen · #16 10-16-2021, 03:08 PM

That makes sense. I've worked on a lot of the earlier 7" sets and don't recall seeing any Moto branded tubes.

bandersen · #17 10-16-2021, 05:47 PM

Rats! After running about 10 minutes, reception dropped off considerably. I hate chasing down intermitent issues. No tapping or wiggling helps. Only leaving it off for a while helps.

dieseljeep · #18 10-16-2021, 06:28 PM

Quote:

Originally Posted by bandersen

That makes sense. I've worked on a lot of the earlier 7" sets and don't recall seeing any Moto branded tubes.

I bought the 7" portable model complete with the antenna and base. The date stamped on the chassis is January 1949. Most of the tubes are original and branded with the manufacturers name, RCA, Sylvania etc.
One of the tubes that aren't original is the ballast tubes. It's an Amperite glass type.

Tube TV · #19 10-18-2021, 02:26 PM

Quote:

Originally Posted by bandersen

Rats! After running about 10 minutes, reception dropped off considerably. I hate chasing down intermitent issues. No tapping or wiggling helps. Only leaving it off for a while helps.

Wow is that ever a minty little Motorola.
As for intermitents, have you tested these two resistors warm? 6 megs and looks like they toasty.

bandersen · #20 10-18-2021, 05:02 PM

No, but I did measure all the resistors in the HV divider cold. They're within spec, but all have between 600 and 1,000 volts across them. They appear to be 1 watt resistors which have a max spec of 500 volts so I suspect all of them.

bandersen · #21 10-19-2021, 11:05 PM

OK, time to stop screwing around and get out a scope!
I monitored the output of the detector and waited for the image to fade out.

Sure enough after about 10 minutes the video signal dropped to almost nothing.

DC voltages and waveforms in the IF seemed OK so I went after the detector assembly. I took the covered off and hit it with a little compressed computer duster can turned upside down to cool it. Bam! image was restored

Now, I just need to determine if it's one of the resistors or the 1N34 diode. My bet is on the diode. I'm not wild about having to perform microsurgery to replace it, but I'l give it a try if I have to.

bandersen · #22 10-19-2021, 11:07 PM

Also started building up a new ballast using small AC motor run capacitors. Works fine, but need to add bleeder resistors. Got a nice jolt when I pulled it out of the socket!

Electronic M · #23 10-20-2021, 12:27 AM

My bet is on the detector diode too. I've had a bad one in a VT-71 before and I've seen others have it go on that model too.

I'd just snip the leads fish it out then do the soldering to reduce the chance of overheating or physically damaging the other parts there.

The nice part about the video detector is that unless someone decides to open the can it's in for some reason nobody else will ever see the modern replacement.

kvflyer · #24 10-20-2021, 02:51 PM

Quote:

Originally Posted by Electronic M

My bet is on the detector diode too. I've had a bad one in a VT-71 before and I've seen others have it go on that model too.

I'd just snip the leads fish it out then do the soldering to reduce the chance of overheating or physically damaging the other parts there.

The nice part about the video detector is that unless someone decides to open the can it's in for some reason nobody else will ever see the modern replacement.

I have had the same issue with that diode. Remember it is an ancient germanium diode. I replaced mine and the picture was immediately restored.

bandersen · #25 10-20-2021, 06:54 PM

Yes, it was the diode. It measure open in both directions. Replacing it with this germanium diode did the trick.

decojoe67 · #26 10-21-2021, 04:50 AM

Nice example of the 9T1 Bob, and nice work, as always. That's one of my fav early compact TV's. I love how the CRT seems to be bulging out of the set. Interestingly, one can't call this one a '40's set because it came on the market in 1950. One of the last of the 3 year run of small electrostatic sets. The only issues with these 8" models is that the CRT's are often found weak and are very difficult to locate. I had to buy a parts set for mine for the CRT and to complete the knob set with brass inserts. The red knobs are very unstable Tenite that want to shrink and lose their medallions. The other issue is that the plastic-weave grille cloth wants to wrinkle and pull from the speaker board. I fixed mine and then it wrinkled again. It's very comfortable to watch compared to the 7" models. Good luck with the resto!

compucat · #27 10-21-2021, 06:50 AM

I have the wood cabinet version of that set and it is very watchable from across the room. These electrostatic sets are quite reliable once properly restored.

decojoe67 · #28 10-21-2021, 08:46 AM

Quote:

Originally Posted by compucat

I have the wood cabinet version of that set and it is very watchable from across the room. These electrostatic sets are quite reliable once properly restored.

Nice. You can call that one the "top-of-the-line" 8" in '50. The key with these Motorola'a, like you wrote, is a PROPERLY restored chassis. A minimalist resto on these chassis's will often leave you with "pie-crusting", intermittent arcing, and/or jittery picture.
The best early electro chassis's proved to be Sentinel (also often used by Crosley and Silvertone) and Emerson. The worst are the Philco's and Hallicrafters due to HV fade.

compucat · #29 10-21-2021, 11:09 AM

Quote:

Originally Posted by decojoe67

Nice. You can call that one the "top-of-the-line" 8" in '50. The key with these Motorola'a, like you wrote, is a PROPERLY restored chassis. A minimalist resto on these chassis's will often leave you with "pie-crusting", intermittent arcing, and/or jittery picture.
The best early electro chassis's proved to be Sentinel (also often used by Crosley and Silvertone) and Emerson. The worst are the Philco's and Hallicrafters due to HV fade.

When I restored mine in addition to a full recap, I replaced all the resistors in the sweep and high voltage circuits. I wanted to have a set I could use regularly and have on and off over the years. Mine was made in 1949 and had the picture tube replaced in 1954. These Motorolas may have been economy sets but they are well made. I always wanted one of the Bakelite Admirals but the twice I bought one it got smashed in shipping. I’ve accepted the fact that no one knows how to properly ship a Bakelite TV.

decojoe67 · #30 10-21-2021, 11:28 AM

Quote:

Originally Posted by compucat

When I restored mine in addition to a full recap, I replaced all the resistors in the sweep and high voltage circuits. I wanted to have a set I could use regularly and have on and off over the years. Mine was made in 1949 and had the picture tube replaced in 1954. These Motorolas may have been economy sets but they are well made. I always wanted one of the Bakelite Admirals but the twice I bought one it got smashed in shipping. I’ve accepted the fact that no one knows how to properly ship a Bakelite TV.

Don't feel bad, I had 2 7" Philco Bakelite shipped with damage. The only way to do it is to have the chassis and cabinet sent separate. Yes, the 8" Motorola's can be marked as '49's, but you'll see them in ads from 1950.