Motorola 9T1 Restoration

[Jon F]

Hey all, I've got a Motorola 9T1 I'm getting ready to restore. I have some questions I'll list below-

Electrical:

-I audited the paper and electrolytic caps with help from the photofact and ordered a cap kit online. I also ordered 1N4007 diodes to replace the silicon rectifiers. Are these directional? Anything special I should know?

-I ordered parts to make a replacement ballast per the attached schematic I found on antiqueradio.org. It was for a Moto VT-73 TS-4J chassis. Will this work with my TS-18 chassis or do I need to swap pins around or change something?

Cosmetic:

-Can I restore the speaker fabric shown in my picture? It is wavy and the color dulled.

-What is the best way to clean and shine the bakelite? I was thinking of trying a magic eraser to clean the years of crud off the surface but not sure it will ruin the finish.

Thanks!!

[Electronic M]

Welcome aboard!

Diodes are ABSOLUTELY 'directional' (the correct term is polarized). The plumbing equivalent to a diode would be a one way valve, and if you connect them backwards your electrolytic capacitors will explode and other rarer parts could be damaged, as soon as you apply power. Electrolytic capacitors are polarized too and will also explode if they themselves are connected backwards.

As per your ballast compare the pin-out of the balast on the TS-4J schematic to the one in the schematic of your set, and IF they are the same AND the two sets have the same tube heater wiring scheme then it should work. If not just use power resistors of the same value listed for the ballast sections in the schematic and it will work fine.

As per the speaker fabric please define what you mean by 'restore'. If it comes off the board easily you can soak it in water to get the dust out, and stretch it taught over the speaker board to make it look nicer. There also may be reproduction cloth available.... Though from the picture it looks fine to me as is.

As per the bakelite that depends on condition. Light dirt and scuffs can generally be dealt with using windex and novus polish. Heavy scratches and fading/stains/sun bleaching can be dealt with by sanding them off, and then sanding with progressively finer grits of sandpaper until the remaining haze can be polished away....Banderson is the expert on that and had a great post about it a few years back.

EDIT: Bakelite is a rather amazing plastic in that it is impervious to heat, and most chemicals, and aside from being a tad brittle (don't drop that cabinet off a table and expect it to land in one piece) it is essentially indestructible.

Welcome!

If you're talking about the Mr. Clean Magic Eraser pads, I think it should be ok to try. They're mild enough that I use them on painted walls and wallpaper.

I use a product called Brasso on bakelite and it works great. However, I understand they changed the formula and it ain't worth a darn anymore (I'm still using a couple of old cans). You could also go to an auto parts store and get rubbing compound. It's used similar to car wax and comes in different grits.

[Zenith26kc20]

You have to add resistors in series with the 1N4007 diodes to make them operate at a slight loss as the original seleniums. If you just use them in place of the seleniums, the voltage will be too high and the electrolytics can be stressed. Also, the set may show problems that are not parts related. My TS-4 had sync problems until I put 33 ohm (hope I remember that right) 5 watt resistors in series with the diodes. By the way, these sets are my favorites! I have one as a daily driver!

[earlyfilm]

Originally Posted by Jon F

Hey all, I've got a Motorola 9T1 I'm getting ready to restore. I have some questions I'll list below-

-I audited the paper and electrolytic caps with help from the photofact and ordered a cap kit online. I also ordered 1N4007 diodes to replace the silicon rectifiers. Are these directional? Anything special I should know?

Yes, they are directional. They are marked, but if you get confused by the markings, measure the resistance both ways and the diodes should be inserted so the low resistance is the same direction in the diodes as it was in the seleniums.

Originally Posted by Jon F

-I ordered parts to make a replacement ballast per the attached schematic I found on antiqueradio.org. It was for a Moto VT-73 TS-4J chassis. Will this work with my TS-18 chassis or do I need to swap pins around or change something?

If you don't yet have the correct schematic for this set go to
http://earlytelevision.org/tv_schematic_diagrams.html
and download one. Usually I prefer the manufacturer's service book.

From this you will see that your ballast drawing is incorrect for this set.

On the ballast tube, pin 6 is a common tie point, a 105 ohm goes from there to pin 7 and a second 105 ohm goes from pin 6 to pin 2. Originally a 37 ohm went from pin 3 to pin 1, but since you are replacing seleniums with diodes, I'd suggest raising this value to 50 ohms to limit the start up current and lower the B + voltage. The final resistor in ballast is a 200 ohm between pins 3 & 4.

>>> Edit: Jon, I made an error here. Bob Anderson is correct and he made a good catch on Motorola's math error! I did not realize that you were using the large capacitor to replace the 105 ohm resistors, in the circuit described by Phil Nelson. That should work, and be more gentle to the tube filament, especially the CRT, in this set. This is the same ballast. However, if it were me, I'd first get the set working with the resistor equivalent ballast while testing, before switching to the cooler capacitor current limiting circuit Phil described, just in case it caused an unexpected prolem. <<<

Originally Posted by Jon F

-Can I restore the speaker fabric shown in my picture? It is wavy and the color dulled.

I tried to soak my cloth off to restretch and it completely came apart. If you try it, I wish you better luck.

Originally Posted by Jon F

-What is the best way to clean and shine the Bakelite? I was thinking of trying a magic eraser to clean the years of crud off the surface but not sure it will ruin the finish.

The simplest way is to use Windex and clean soft rags. Once the cabinet is clean, give it a good coat of paste floor wax (preferred, but auto wax can be substituted.)

One possible issue you may find is the adjustment for the gimmick on the 1B3/8016 is slightly different from the illustration since modern 1B3/1G3 has a different cathode-to-plate spacing. If you have to replace the tube, or if someone has moved the spring, you will have to do a little playing to find the sweet spot.

I owned one of these sets and used it as my daily driver from 1956 to 1964. I still regret selling it.

Today a good 8BP4 is almost impossible to find. I've seen the smaller and much more common 7JP4 substituted in these sets.

James.

[bandersen]

I have to disagree - the ballast drawing is correct for this set. It does show pin 6 as the common tie point and capacitors are used in place of resistors to eliminate the waste heat.

The original 105s are too small if you add up all the tube filament voltages (75.4 and 81.7) you get around 140 and 120 for the resistors. I imagine Motorola was stuck using the same ballast as earlier models with different tube line ups. When I crunched the numbers though I found that 8.2uF is a better choice than 10uF. Here's the original discussion thread: http://videokarma.org/showthread.php?t=249434

Also, I've actually reduced the 33 ohm resistor to boost the B+ in some sets to make them run better.

The grille cloth is woven plastic and can be cleaned with a mild detergent and a sponge or cloth. I haven't bothered trying to flatten one out. Possibly pressure and heat would work but I don't think it's worth the risk.

I've been using Novus #2 follow by Meguiars Cleaner or Tech wax lately with good results. Only wet sand as an absolutely last ditch effort.


Good luck!

[Jon F]

Thanks for the wealth of information. I dug into the set and replaced all of the paper capacitors which I got in the mail recently.

As far as the e-caps, can someone help with what pins they go to under the chassis? I figured out C1 pretty easily using the schematic, but C2 & C3 I am not sure about.

Still waiting on the diodes and resistors so hopefully can do the silicon rectifiers and ballast next week.

Pics attached, cleaned up chassis, before and after paper caps.

[bandersen]

Looking good. There are symbols (triangle, square, half-moon) next to the lugs on the capacitors. There should be a legend printed on the capacitor indicating which symbol is which cap.

[Jon F]

I never noticed the symbols before. Are the inside leads always the negative and the outside the positive (or vice versa)? How can I tell what leads correspond with each other since the symbols are only on the inside leads?

Thanks!

[bandersen]

The can is common negative for all the capacitor sections. So all the outside leads are connected together. Be careful not to connect the new capacitor negative leads to the chassis. It's floating and not connected to the circuit ground.

[Jon F]

Makes sense. Got the diodes today, they are very small comparatively. Should I wire the resistor before or after the diode?

[bandersen]

It doesn't matter

[Jon F]

I assembled the replacement ballast today, not the prettiest but if it works I don't really care so much. I ended up putting 2 100ohm resistors in series for the 200ohm shown on the schematic, and also a 27ohm instead of the 30ohm, just due to what I had.

[Jon F]

Got a little bit of time today to look at the chassis. I built a bulb tester per the attached to try to power the set before I replace the rectifiers and electrolytics.

Well, I put a 10hm 10watt resistor on pins 1 and 14 of the CRT socket and flipped the switch and the 15 watt light bulb immediately turned on bright. So I switched is off right away, I guess I have a short somewhere. I don't see anything by eye, where do you guys think I should start checking?

Or just replace the Ecaps and silicon rectifiers and try again?

[old_coot88]

Try a few progressively-higher wattage bulbs.
If a say, 75 watt bulb lights up as bright as the 15 watt one, that would indicate excessive current draw.