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!

[TV-collector]

[QUOTE=bandersen;3256220]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



Congrats to YOUR YARDBIRDS-shirt!
I would like to have one, too!
One of the best 60s groups!

Btw., Your ADMIRAL model was part of a Perry Mason episode, in which is was stored inside a garage.
That means that it was taken out of work after about 12-14 years or so.
I own the version with the flat front screen panel.
Just like yours with a 10" CRT and 2 chassis.


Regards,
TV-collector

[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!

[dtvmcdonald]

Originally Posted by Yamamaya42

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

Or Deoxit D100L, which is not a spray like D5. You apply with a small artist's brush. 2 cc of D100 is enough for a large TV.

[Chris K]

Originally Posted by dtvmcdonald

Or Deoxit D100L, which is not a spray like D5. You apply with a small artist's brush. 2 cc of D100 is enough for a large TV.

...and don't use either on wiping resistor potentiometers like most volume and adjustment controls for brightness, horizontal hold etc. Use Deoxit Fader spray. It won't eat the insides like regular DOx will. Ask me how....well, you know.

[Madeline12]

Originally Posted by 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!

As much as it must have sucked, your sharing of past experience is VERY helpful. The CRT was also my first plan of attack… I pray it’s still functional but I have yet to get a good look (been a bit busy with the job sadly 🙄 hopefully this weekend). Anyways, all noted, thanks!

Originally Posted by JohnCT

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

Sounds good, I will be doing so. Rather not waste all this time if I can determine that there’s very little chance of resolving the current issues.

Originally Posted by Electronic M

Some recapping advice: never go lower on voltage rating (you can go higher, although more than double typically isn't recommended), but never lower. There are pre-war and post-war standard capacitance values. Both coexisted in the 50s-70s but the pre-war values are either NLA or stupid expensive. Prewar standard capacitance uF values were 10, 20, 30, 40, 50, 60, 70, 80, post-war values are 10, 22, 33, 39, 47, 56, 68, 82 and various decimal relocations there of. Don't waste your money on pre-war value parts....Get the closest post war capacitance value and you'll be fine (especially on lytics where the original tolerance was shockingly broad). On multi-section electrolytic caps use several single section caps to replace it....There are companies that make replacement multi-section caps but they are generally not worth it unless you are restoring a holy grail model worth 4 figures.
Short leads can make things harder. Just radios and Bob's capacitors both only sell parts with good lead length, but are more expensive and shipping takes a long time. I typically buy from Mouser or digikey. For lytics I favor Panasonic, Nichicon, and Illinois Capacitor, for film caps Panasonic (especially the red ceramic cased film caps), Illinois Capacitor, and WIMA. You have to look at the data sheets and part numbers to make sure you're ordering the long lead film caps.

Don't replace capacitors under 1000pF/uuF which are almost always mica...On the flip side caps 1000pF=.001uF are just about always paper (and should be replaced) even if they're disguised in the same domino cases associated with micas.

Was unaware about the tidbit regarding the paper caps… VERY happy that you shared that. I’ve been hunting down some of the electrolytics stated in already… seems some are pretty tough to find already (10uf 600V… yeesh). Still looking though. Thank you!

Originally Posted by Chris K

...and don't use either on wiping resistor potentiometers like most volume and adjustment controls for brightness, horizontal hold etc. Use Deoxit Fader spray. It won't eat the insides like regular DOx will. Ask me how....well, you know.

Haha yes, I also have F5. I usually use it on sliders, but considering how much older this thing is compared to my usual repairs you may be correct. Thanks!