Absolute beginner (in terms of vacuum tubes/tvs) and I will need many tips…

[Madeline12]

Hello!

Newbie here… my previous experience has been with solid state audio gear. However, for some time now I’ve been interested in taking a shot at tube powered electronics. Recently, I came across a Stewart-Warner 9121a from 1951. It’s beautiful, but it’s got some issues… and I’m very interested in restoring it. Some issues I’ve noticed:

1. Sound is present, but there’s some static occasionally and when rotating the knobs. I imagine the pots just need deoxidizing like solid state gear though.
2. No picture. I saw on another thread that holding your hand close to the screen and checking for static is a good diagnostic test. I did not feel any static. In addition, I saw no faint picture produced over the course of a few minutes in a pitch black room.

I have so, so many questions… too many to list frankly. I’ll try and keep it relatively short in this this thread though:

1. First and foremost: the most important thing for me regarding this project is safety, obviously. My hesitancy up until this point is due to the dangers involved with working with tubes. I’ve spoken to someone who’s worked on and studied tube gear (radios and TV) for years, and my uncle who also has worked with tubes and is an electrician. However, I’d love as many resources as I can get to ensure I can do this as safely as possible.
2. At any point, am I able to touch the chassis? I understand it can hold charge even when it’s been off for some time, but I’m having difficulty seeing a way to access parts and tubes without touching it in the future.
3. I’m happy to share a picture if needed, but weirdly underneath the emblem in the interior there seem to be potentiometers with no knobs. There is also one that doesn’t seem to be a potentiometer… more like a screw with threads. These are not the exterior knobs that control the radio/volume/etc. Anyone know what these may be for off the top of their head?

Again, I am MORE than happy to provide any additional info/pics upon request. I greatly appreciate any help or tips people may offer.

Thanks!

EDIT: thought I’d add a pic of the odd pots/screw that were inside the plaque below the screen.

[old_tv_nut]

1) SAFETY
The retained charge you are worried about is the high voltage - painful but not fatal. You can learn how to discharge the high voltage safely with the set turned off.

MUCH MORE DANGEROUS is the power line voltage. You need to find out if this set has a "hot chasssis" (connected to one side of the power line). Even if it isn't a hot chassis, powering through an isolation transformer is a good idea.

It's a big jump to work on a TV without having done something simpler like a radio, but it is doable with coaching.

Before starting, you need to obtain a schematic diagram and service information.

[Madeline12]

Originally Posted by old_tv_nut

1) SAFETY
The retained charge you are worried about is the high voltage - painful but not fatal. You can learn how to discharge the high voltage safely with the set turned off.

MUCH MORE DANGEROUS is the power line voltage. You need to find out if this set has a "hot chasssis" (connected to one side of the power line). Even if it isn't a hot chassis, powering through an isolation transformer is a good idea.

It's a big jump to work on a TV without having done something simpler like a radio, but it is doable with coaching.

Before starting, you need to obtain a schematic diagram and service information.

Hey, thanks for the reply! I may have the opportunity to be supervised while doing this by a pro, fingers crossed. I do have access to the schematics, and am hoping to procure the service manual soon. It’s available in the print form currently, but I’m searching first for a pdf. But it’ll be a backup.

Thanks for the info, I will be researching this asap!

[Yamamaya42]

First, you should consider yourself lucky that it did not go up in smoke when it was powered on, normally for something like this, it's brought up very slowly via dim bulb or a variac, but if you got sound, it means power is working to some degree, and this is a good start.

This set is not a hot or floating chassis type, so you are safe there, it has 2 LV rectifiers off the main transformer.

Normally the first step would be to replace the electrolytic capacitors in the power supply, and then all the paper capacitors, (there will be a lot of them), and then check for bad resistors.

There is a ¼ watt fuse that protects the flyback transformer, if by chance the horizontal oscillator failed to start, the horizontal output would have overloaded and blown this fuse to protect the flyback.
Take a close look at it

also, is seems this set has a 16KP4, magnetic focus with an ion trap, pay close attention to the position of the items on the neck of the CRT if you take them off, so you can put them back in the same place!

[Madeline12]

Originally Posted by Yamamaya42

First, you should consider yourself lucky that it did not go up in smoke when it was powered on, normally for something like this, it's brought up very slowly via dim bulb or a variac, but if you got sound, it means power is working to some degree, and this is a good start.

This set is not a hot or floating chassis type, so you are safe there, it has 2 LV rectifiers off the main transformer.

Normally the first step would be to replace the electrolytic capacitors in the power supply, and then all the paper capacitors, (there will be a lot of them), and then check for bad resistors.

There is a ¼ watt fuse that protects the flyback transformer, if by chance the horizontal oscillator failed to start, the horizontal output would have overloaded and blown this fuse to protect the flyback.
Take a close look at it

also, is seems this set has a 16KP4, magnetic focus with an ion trap, pay close attention to the position of the items on the neck of the CRT if you take them off, so you can put them back in the same place!

Thanks for the tips! All have been written down and noted for when I feel comfortable proceeding sometime soon. Especially that last paragraph, very valuable to know.

[bandersen]

Here's a copy of the Riders service info: https://drive.google.com/file/d/1_EZ...ew?usp=sharing

I've put together a beginners series on restoring TVs like yours you may find useful.

https://www.youtube.com/watch?v=ShgX...xkxFV3Y20pv6Nb

Here are the controls you asked about.

[Madeline12]

Originally Posted by bandersen

Here's a copy of the Riders service info: https://drive.google.com/file/d/1_EZ...ew?usp=sharing

I've put together a beginners series on restoring TVs like yours you may find useful.

https://www.youtube.com/watch?v=ShgX...xkxFV3Y20pv6Nb

Here are the controls you asked about.

Wow, EXACTLY the stuff I’m looking for! Can’t thank you enough Will be watching this, and thanks for the doc!

[Yamamaya42]

One thing that caught my eye right away about this set as a potential point of failure was the rotary switches used in it for bias, filament power and other signals, if they have corroded / oxidized, it could cause problems.


Has anyone worked on one like this here?

[bandersen]

I've worked on combo sets with similar switches for cutting juice to the TV circuits. Yes, it is hard on the switches and they should be inspected/cleaned.

[Madeline12]

Originally Posted by Yamamaya42

One thing that caught my eye right away about this set as a potential point of failure was the rotary switches used in it for bias, filament power and other signals, if they have corroded / oxidized, it could cause problems.


Has anyone worked on one like this here?

Originally Posted by bandersen

I've worked on combo sets with similar switches for cutting juice to the TV circuits. Yes, it is hard on the switches and they should be inspected/cleaned.

Writing down as we speak much appreciated!

[Yamamaya42]

DeoxIT D5,, it ain't cheap, but it really works well!

[Electronic M]

The service adjustments with the threaded shafts are tuned inductors or tuned transformers...the tuning is magnetic permeability tuning. The screw threads move a small slug of ferrite or copper in and out of the core of the coil. Unless they are physically stuck (and you need to adjust one for some reason) and can't move they don't require or benefit from cleaning. Also if the tuned coil is not in the horizontal circuit DON'T turn it at all....Most tuned coils/transformers are in the tuner and IF circuits. The tuner and IF stages require precise electrical alignment for the set to function...This alignment 97% of the time is still fine as it sits today. If you disturb any tuner or video IF adjustments you will have to buy a lot of very expensive equipment and spend a large amount of time learning the borderline dark art of television alignment.

TV chassis can only have voltage on them if plugged in to the wall, and that usually only goes for hot chassis sets. The capacitors can store voltage, the lytics and CRT are the only ones that can hold it long enough to get you. The lytics typically self discharge within a minute (you can take a clip lead connect one end to chassis and touch the other end to the positive terminals to ensure discharge if you're worried), but the CRT can hold it's charge for days....The good thing about the CRT is it can only store an amount of charge that is close to the worst static charge you can get shuffling feet on carpet and touching a doorknob, but it's still bad enough to trigger reflexes (and what you elbow on reflex can be sharp...ask me how I know) so if you need to poke around in the HV cage or remove the CRT discharging the CRT is strongly recommended. To do so connect an end of a clip lead to chassis, connect the other end to one end of a 1M ohm resistor, connect the other end of the resistor to the metal blade of a well insulated screwdriver, then holding the driver by the insulated plastic handle slide the blade under the HV suction cup connector (some 50s sets don't have a suction cup and just leave the metal connector exposed) on the side of the CRT and hold it to the metal for 30 seconds.
You can do without the resistor and connect the clip lead directly to the screwdriver but that allows a phenomenon in CRTs known as dielectric recovery where a fair portion of the charge magically reappears after a few seconds or minutes.... I've been bit by it and uttered more swear words because of it than I can remember.

[Madeline12]

Originally Posted by Yamamaya42

DeoxIT D5,, it ain't cheap, but it really works well!

I actually do have some for my solid state repairs, so I will be applying that here as well

Originally Posted by Electronic M

The service adjustments with the threaded shafts are tuned inductors or tuned transformers...the tuning is magnetic permeability tuning. The screw threads move a small slug of ferrite or copper in and out of the core of the coil. Unless they are physically stuck (and you need to adjust one for some reason) and can't move they don't require or benefit from cleaning. Also if the tuned coil is not in the horizontal circuit DON'T turn it at all....Most tuned coils/transformers are in the tuner and IF circuits. The tuner and IF stages require precise electrical alignment for the set to function...This alignment 97% of the time is still fine as it sits today. If you disturb any tuner or video IF adjustments you will have to buy a lot of very expensive equipment and spend a large amount of time learning the borderline dark art of television alignment.

TV chassis can only have voltage on them if plugged in to the wall, and that usually only goes for hot chassis sets. The capacitors can store voltage, the lytics and CRT are the only ones that can hold it long enough to get you. The lytics typically self discharge within a minute (you can take a clip lead connect one end to chassis and touch the other end to the positive terminals to ensure discharge if you're worried), but the CRT can hold it's charge for days....The good thing about the CRT is it can only store an amount of charge that is close to the worst static charge you can get shuffling feet on carpet and touching a doorknob, but it's still bad enough to trigger reflexes (and what you elbow on reflex can be sharp...ask me how I know) so if you need to poke around in the HV cage or remove the CRT discharging the CRT is strongly recommended. To do so connect an end of a clip lead to chassis, connect the other end to one end of a 1M ohm resistor, connect the other end of the resistor to the metal blade of a well insulated screwdriver, then holding the driver by the insulated plastic handle slide the blade under the HV suction cup connector (some 50s sets don't have a suction cup and just leave the metal connector exposed) on the side of the CRT and hold it to the metal for 30 seconds.
You can do without the resistor and connect the clip lead directly to the screwdriver but that allows a phenomenon in CRTs known as dielectric recovery where a fair portion of the charge magically reappears after a few seconds or minutes.... I've been bit by it and uttered more swear words because of it than I can remember.

Good to know! I will be watching out for that… rather not drop any more money if I can help it

[Chris K]

I'm a little more advanced but not much! I've managed to get a couple dozen of these postwar sets up and functioning pretty well. I love most the TVs from 1947-1955 with RCA as a favorite brand. All sound advice here. I'll add a couple from a beginner's perspective. Wait until the real experts here chime in and point out any mistakes I've made before you employ my suggestions as technique:

1. All of the warnings regarding hot chassis, high voltage often in the 10Kv range and above are the first and foremost thing that needs to be respected. One thing I've heard is the HV anode can really hurt but the voltages in the flyback can kill you. High capacitance, new and old, electrolytic caps can hold charge for a while, especially ones in the power section. They don't hurt...they just give an uncomfortable buzz.

2. Don't buy cheap, hard to believe how many you can get, electrolytic and film capacitor "sets" from China. When I searched Amazon, I was astounded I could get 100uf electrolytic filter caps at a little more than a dollar per cap, so I bought a ton of them. They caused more issues than they were worth. I could not run down a horizontal instability issue in an 8" RCA PT-8-3034. Turns out it was the main "Uxell" filter cap in the power supply that created all the issues. Don't buy cheap stuff. You can use these to test something...just as a tack in but don't rely on them for service use and if you have a problem, suspect them first.

3. If you buy old analytic equipment, be sure it's working well and you can trust the results you are getting. Again, a lesson I learned in the TV school of hard knocks.

4. Don't replace everything first and then test. Start with the power supply. I have a dim bulb setup and I start running the TV with a 60 watt bulb for about 15-20 minutes and then progress through 100, 150, 200, 250 and 300 watts. REMOVE the lead off the horizontal output tube until you get to the higher wattage bulbs. The horizontal oscillator will not start until it gets a certain voltage and the lack of oscillation can drive excess voltage through the Horiz. Output Tube (HOT) and fry it. If I suspect the main power electrolytic caps are bad and can't be reformed or test shorted, I'll replace them before first power up. A shorted electrolytic in this section can fry the power transformer. Ask me how I know that!

5. Service Power, Sweep and get a raster...then go for a picture. Check the TV function often if you can. Don't get carried away and replace a dozen caps and resistors to find you don't have a working TV. You won't know where to start to run it down. If you test...replace...test etc. it's the easiest way to be sure you don't create issues rather than solve them. Again, ask me how I know that!

6. Find the expert restorers on YouTube and watch their videos. My go to are Bandersentv (he posted in your thread) and Shango66 but there are many others.

7. Test the CRT before you do anything else. A dead and rare CRT is usually a showstopper unless there's a way to modify the circuit and substitute it with another type CRT.

I'll probably think of more from the rookie mistake file I have. The experts here sometimes forget how stupid the novices are! Not their fault. When you talk like you know what you're doing they assume you know what you're doing!

[JohnCT]

Originally Posted by Chris K

7. Test the CRT before you do anything else. A dead and rare CRT is usually a showstopper unless there's a way to modify the circuit and substitute it with another type CRT.

There are three other "hard parts" (auto transmission reference) in a TV that can be showstoppers besides the picture tube - flyback/HV transformer, deflection yoke, and power transformer. The vertical output transformer can also be an itch but those are easier to fudge with a similar but not exact replacement.

Your idea of rebuilding the power supply is a good one (I'd disconnect the chassis and use a dummy load). This will at least eliminate the power trans. Getting the sweep up next is also a good idea. If you can get HV, then fire the parts cannon at it.

John