Motorola 9T1 Restoration
 

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!!

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.

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!

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.

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. <<<



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

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.

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.
http://farm6.staticflickr.com/5279/7...e45174e1_z.jpg

Good luck!

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.

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.

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!

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.

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

:thmbsp:

It doesn't matter :)

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.

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?

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.

Right, 15 watts is way too small. The 9T1 draws around 100 watts so that 15 watt bulb looks like a dead short in comparison. I'd even go higher than a 75 watt bulb if you can.

Tried a 60 watt bulb, lights up just as bright. I went ahead and swapped in diodes for the rectifiers and no change, bulb still lights.

I'll try to find a 100 watt bulb and see...

Do the tube filaments light up ? They won't be full brightness with that bulb in series, but with the lights out you should see a glow.

Tried a 200 watt bulb and it still lights dimly.

Left on just long enough to check tube filaments. All light up after some re-seating.

That's good. A 200W bulb will still glow with a 100W set.

Indeed, after the set warms up for 30 seconds or so I can get some music from a local radio station(Q877) that is the same freq as CH 6.

Looking promising, I have to replace the remaining ecaps, and then is there anything else to check before I try with the CRT? What is the discharge procedure for this set after I turn it off, as it does not have the typical HV lead to the tube? (I assume the HV is run in the neck connector)

Nothing else to check that I can think of. Right the HV is one of the base leads. The CRT doesn't have an aquadag coating so doesn't buildup a HV charge like it's bigger cousins. Good luck.

The HV should discharge it's self within a couple minutes after being turned off.

Thanks guys, just finished the electrolytics, so far I've replaced all paper caps, all electrolytic caps, & selenium rects are now diodes with 30ohm resistors.

Powered it up with the CRT, got a decent raster but no image. The picture also doesn't get any taller than in the image below. I do have sound. No idea where to go from here. Unfortunately I don't own a tube tester so I have no idea the state of the tubes in the set.

Any ideas before I order some tubes to swap out?

Thanks!

If the video detector crystal diode is bad it could cause there to be no video. You can probably grab a decent sub at radioshack and try subbing the original.

To go along with what Tom has said, I had the same issue with my VT-71. The diode was indeed open. Below is my restoration thread on ARF. It goes on several pages but you can see the progress and solution. Unfortunately, the images have gone away over the years. I only found this thread using a google search.

Hope you are able to get 'er goin' as they say.

http://antiqueradios.com/forums/view...p?f=3&t=144209

BTW, I host my own pictures now so that they won't go away when the forums have upgrades.

Thanks for the tips, per the thread I removed the rectangular can, and checked the diode with my multimeter. It reads a voltage drop of 0.31V which seems normal.

I left the set plugged in for a few minutes (without the light bulb) and after messing with the controls I did get a low contrast image, see attached.

The tubes on the set are getting pretty hot, too hot to touch, is that normal?

Tubes get hot.

Glad to see that picture!

Thanks, I attribute not getting a picture at first due to my ignorance on how to properly adjust the set.

With the brightness all the way down, and the contrast all the way up, I get the best picture. With an RF modulator, the image is still rather noisy, and the sound has an awful buzz, but I'm really glad what results I've gotten so far.

Nice! Something to keep in mind when using OTA channel 6 as a test signal is that the sound carrier is much stronger than the video. I usually get booming sound with just a scrap of wire for an antenna but need a good antenna to get a decent image. I'm a couple miles west of downtown BTW.

Thanks, I'm at thereabouts also, you probably live down the block and I don't even know lol.

Anyway, any tips on how to clean up the picture? Any tubes to replace?

Thanks!

It's hard to say. Could be the way the RF signal is being injected, weak tubes, bad alignment, bad caps/resistors, etc.

Check the easy thing first - the antenna connection. There are three screw terminals on the back. If you have a 75 ohm source, use the top two screws, If it's 300 ohms, use the outer two screws.

As for tubes, there should be several 6AU6 or 6AG5 in the IF sections. You can try swapping those around if you don't have any spares.

Also, since you're local, you could swing by my place and I can check it out for you.

Guess what, I found a small "hidden" paper cap I missed, 0.004mfd @600V. I replaced it an the picture cleared up, and my height is restored.

The H and V holds are now unstable though, very touchy. Also, seeing some retrace lines. I am going to check some resistors near the brightness control for the retrace lines. I am also going to look at replacing some tubes that hopefully will help the hold issue.

So cool to view the restoration of this vintage set.

These sets were kinda unstable when new.

If you have a scope, check to see if the sync separator is working properly. If not check for voltages off spec in that circuit. Try substituting the sync tube.

Oh the retrace issue, remember this set is electrostatically swept and therefore you don't have the usual big voltage signals being generated that normal B&W TVs use to key the blanking. In fact, the high voltage oscillator is not even running on the horizontal sweep frequency in this set! To the best of my knowledge there is no blanking in this set, other than the video itself.

All the Motorola 7's and most other 7 inch electrostatic sets have iffy blanking. If memory serves me correctly the 8BP4 you have uses the same electron gun as the 7JP4 with simply a larger bulb on the other end and the 8's seem to be a bit more critical on retrace than the 7's.

I assume that you have replaced all the 6KV capacitors in the set and the paper capacitors in the video output stage, especially the one going to the cathode of the CRT. Make sure the 100K resistor going from the filament of the 1B3 to the anode (pin 6) of the CRT has not increased in value. Check the value of the 150K resistor between the control grid of the HV Osc. and the ground. (That is High Voltage osc. and not the Horizontal Sweep osc.)

Your next step is to adjust the high voltage. To do this on this set, turn the set off channel and and lower the brightness slightly. Using a plastic stick gently slide the gimmick (the spring around the belly of the 1B3/8016) up and down while adjusting the screen for the maximum brightness. After this, readjust the focus. Now feed a signal into the TV and adjust the brightness and contrast the best you can to get rid of the retrace.

James

For the price it would cost you to order a single compliment of tubes to swap out, most of which you aren't going to need, you can just buy a decent used tube tester. The main thing to think about with a tube tester is what era is going to be the focus of your interests. Reason being, a tester from say the 50s obviously would not have the capabilities to test tubes from equipment made/designed in the 60s or 70s. Inversely, a later tester will not have the capability more than likely to test old "big pin" tubes from 20s-30s radios and such. I keep a couple just for these reasons and finally some test C.R.T.s and others don't, so that's something to think about as well.

Thanks for all of the tips guys, being my first vintage TV resto I am pleased with it so far.

Thanks for the tip on the HV, never knew how to set properly. Once I get all of my tubes squared away I'll also set the voltage.

I am pretty sure one of three 12SN7GT's I have in my chassis is flakey, as depending on how I suffle them around in the chassis I can lose all picture reception.

I have been watching a few tube testers on ebay in the $50 range, I will likely bid on one this week or so.

Also, are replacements of the power switch/volume available? I typically have to jiggle the volume knob in order to get a full sounding audio, or else it is just treble.

:thmbsp:

Be aware that the older the tester, the more restoration it's likely to need, just like any other device of the same vintage. Something like a Sencore Mighty Mite will cover the tubes commonly found in vintage TVs, and it's new enough that you can probably just plug it in and use it.

http://www.antiqueradio.org/art/Phil...40TubeTest.jpg

Some tube functions (notably, oscillation) can't be tested on any tester. In those cases the best test is substitution with a known good tube. In a few such cases, I've had to try as many as half a dozen "tests good" tubes before I found one that oscillated properly in a particular TV.

Regarding the volume, have you already tried cleaning the volume control? See: http://www.antiqueradio.org/FirstStepsInRestoration.htm .

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

I did try spraying cleaner in the control, and then even took it apart to try to bend the contacts tighter but no improvement.