Motorola 9VT1

[cameronflyer]

Great night guys,
I finally got my capacitor ballast built for my 9VT1 and powered her up for the first time with a resistor substitute for the CRT. Once she warmed up I got some noise from the speaker (mostly hum from the florescent lights in the TV shop) but some static. After checking a few voltages and not finding to much out of place I worked up the courage to try an untested 7JP4 from my Admiral 19A1 I didn't want to risk my 8BP4 just yet. After a few seconds she lit up, I could see a raster with the lights in the shop off. I then installed my 8BP4 and crossed all my fingers and toes and turned her on. I am happy to say it looks like I have a good 8inch CRT!!!! A bit brighter than the 7JP4. Now time to finish recapping her and see what else pops up in her restoration.
I do have a question though. I used 20watt resistors on the rectifier side of the ballast and they are running warmer than I expected. Not to warm for a 20watt but warmer than I thought it should be. I should ad that I used a CL90 from the ACline to the ballast and she is drawing .8 amps roughly at 115v AC on the line through my sencore variac. My question is is this normal? Thanks in advance.

[cameronflyer]

One more thing to add. I replaced the selenium rectifiers with modern silicon ones.

[earlyfilm]

Originally Posted by cameronflyer

I finally got my capacitor ballast built . . . . .

I do have a question though. I used 20watt resistors on the rectifier side of the ballast and they are running warmer than I expected. Not to warm for a 20watt but warmer than I thought it should be. I should ad that I used a CL90 from the ACline to the ballast and she is drawing .8 amps roughly at 115v AC on the line

Congratulations! Most 8BP4's went gassy and developed a brown center spot.

Sam's 83-6 says "RATING: .9 Amp at 117 Volts AC" so you are quite close. I'd have estimated a little bigger draw if you have not yet replaced all the small capacitors, especially the plate to grid ones.

Re: Heat from B+ current limiting resistor.

Well, remember the wires in a normal ballast glow red hot and that was the reason for the little square of asbestos that was in side the cabinet over the ballast.

I'd sure keep that resistor above chassis in an old ballast shell and the filament capacitors safely under the chassis away from the hot resistor(s).

Jas.

[bandersen]

I'm not sure which resistors you are referring to ? Are these ones you added in series with the silicon diodes ? What value did you use ? I usually leave them out altogether. it really doesn't effect the B+ that much and the sets run cooler. The service info states 0.9 amps @ 117 so your resistors might be too large.

[bandersen]

I just read earlyfilm's post and am a little confused. What are you using for a ballast ? One you made yourself with capacitors and resistors or an original one ?

[cameronflyer]

Hi Bob,
I used 2, 10uf AC caps and 2, 33ohm resistors 1 each for the filament strings. I also used a 37ohm before C1 and a 200 after the rectifier M1 both @ 20watts.

[bandersen]

You used 33 ohm resistors in series with the 10uF caps ? That really isn't necessary.

So it's the 37 ohm and 200 ohm resistors that are getting hot ? They do normally get pretty toasty.

[cwmoser]

I also acquired a Motorola 9VT1 a month ago.
Its in the pipeline to be restored.
Your 9VT1, mine, and a 9T1 (similar circuitry) are being
represented here. Have not tested my 8BP4 CRT yet.

Carl

[cameronflyer]

Great to hear that we a restoring at the same time Carl.
I got most of my caps changed last night should finish up tonight accept for a couple of electrolytic s that haven't arrived yet. Hopefully I don't have any mica cap troubles. Mine is the strait TS-18 Chassis, there are a couple of minor production changes that are not reflected in the schematic that are driving me a bit crazy but not to much. C5 off of pin 7 in V4 of the second IF isn't there looks like it never was , and C26 on pin 6 of V3 the 1st IF is a .1 instead of a .5 as shown on the Sams . If anyone knows why please let me know. The .1 looks like it came from the factory, and the set does run with it that way so who knows. So far all the resistors I have checked are within tolerance keeping my fingers crossed on the rest.
Quick question to BAndersen. I know you have restored a few of these Bob. are there any smoking guns I should look out for? I would also appreciate any input on my Cap conundrum.

[bandersen]

I've seen some production variations in the IF circuits too. If it looks like it's original, I'd just go with that value and see how it plays. I'm surprised you haven't found any out of tolerance resistors though. I've had to replace a bunch in every set I've worked on. Especially the low valued ones ( < 1000 ohms) in the IF circuits. As for smoking guns there's the ballast, selenium, electrolytics stuff you've already been working on. Also you may have some issues with linearity and height that swapping the 6SL7 can cure.

[cameronflyer]

Thanks Bob,
I did have linearity problems swamped the tube tonight and cured it thanks for the hint. The good news is I have a picture and sound tonight after replacing the remainder or the paper caps. I do have some horizontal tearing until she warms up and a hum bar in the picture. I have 2 electrolitics that haven't been replaced yet that I'm sure are causing that problem. So far I've been very fortunate , the 8bp4 CRT looks like new. I'm a happy camper so far thanks so much for all the help. At this point im sure this is a low time set, although she has no origanal tubes in her she only had one or 2 caps replaced. I will post pictures soon.

[Jon F]

Hi, what value resistor did you use to replace the crt for testing, and what pin #s should be connected?

[earlyfilm]

Originally Posted by cameronflyer

C5 off of pin 7 in V4 of the second IF isn't there looks like it never was , and C26 on pin 6 of V3 the 1st IF is a .1 instead of a .5 as shown on the Sams . If anyone knows why please let me know. The .1 looks like it came from the factory, and the set does run with it that way so who knows.

If you check the factory schematic also on the ETF website, you will notice the electrolytic called C-5 by Sams is not present and there are some other changes in the 1st & 2nd IF circuit.

Remember when using two sources, that the component C, R and V numbers probably won't be the same and they are not the same here.

James.

[Electronic M]

Moto had so many production changes on their electrostatic sets that finding a matched TV set/schematic pair can be a challenge. If it looks original underneath use the schematic as more of a conceptual tool for how it works / signal flow, and replace parts based on what is actually installed in the chassis.

[cameronflyer]

Jon f , if I remember correctly I used a 10 ohm resistor on pins 1 and 14.