Hello,

today I have fired up the RCA 9-T-246 for which I asked for the schematics. Steve Kissinger sent me a copy, thank you very much.

After cleaning the set, it was full of asbestos, I reformed the electrolytics and checked the chassis and the tubes for faults. Nothing significant was visible.

When I switched it on with a variac, I could hear no wistle from the line output unit. I checked input signal of the line output tube 6BG6 at the junction R183 and C160 with the scope. The sawtooth should be 40 Vpp, but I only get 30 Vpp. At the grid, there should be -110V, the reading was -100V.

With signal and a readjustment of the ion trap, I got the first light on the screen (see photo). Like I measured before, horizontal width is too small. At pin 5 (6SN7-GT) of the line oscillator, there should be 54V, the reading was 38V. All voltages in the oscillator unit seem too low. Does somebody has a suggestion?

- Eckhard

Check your B+ at the 5U4 see if that is low. Perhaps your caps arn't reforming as well as they should. Check the value of the resistors feed the osc stages. Check around the damper for low boost voltage. Try replacing the 5U4 and the damper tube .
Good luck
Terry

That is very encouraging progress for an unrestored TV of that age.

I have had poor success with reforming old electrolytics. Some will reform, but in my experience, they will either perform badly or fail before long.

I would replace the electrolytics to prevent future damage. If you are concerned about authentic appearance, of course you can restuff the original cans with new capacitors.

Until I have replaced electrolytics and performed voltage checks around the set, I don't try to diagnose more specific problems. There are too many possible causes -- including bad paper capacitors, dirty/corroded controls, and so on.

Just my opinion :-)

Phil Nelson

Hi,

the power supply with the 5U4 is working properly. All the B+ voltages are in correct values. Even with 50 Hz, there is only a little hum in it, less than I have expected. I have replaced the booster capacitor, but without success. The difference of the cathode voltage related to the grid voltage of the 6BG6 is only 8v. It should be 20v.

In the attachment you find the schematics with the recent readings and a screenshot. Any suggestions?

- Eckhard

Meanwhile I have got full width with two changes:

- added a capacitor 20 nF parallel to C159
- changed R184 to 150 Ohms.

But this is not the final decision. I assume that the 6BG6-G, which I tested well, does not provide enough current. I will try to get a spare tube.

Here is a screenshot. Note that the screen color is blue due to the indoor white balance of the camera.

- Eckhard

If you haven't already, I'd recap all the wax capacitors. Do several as a batch (each cap one at a time, remove and immeduately replace so you don't forget where it goes) and turn the set on to confirm it still works right. Looks like all the hard to find parts, lyback, yoke, CRT, and such are good.

I'm amazed it made it across the big pond intact...Nice score Eckhard !

I'm amazed it made it across the big pond intact...

I have got this set free from a collector who moved into the U.S.A. last year.

If you haven't already, I'd recap all the wax capacitors. Do several as a batch (each cap one at a time, remove and immeduately replace so you don't forget where it goes) and turn the set on to confirm it still works right.

I don't want to use this set as a daily watcher, so it is my philosophy to replace only those caps in such old tv sets which are absolutely necessary. I have replaced two caps in the line output unit, but I will replace them with the original ones due to the fact that they are OK. New plastic caps do not fit in such an old device. They look horrible on the chassis.

On the bottom of the chassis I found some yellow-black caps. Are these caps original or replacements from earlier years?

- Eckhard

And, no matter what you think, that would be all of them. All the symptoms you show would be caused by the faulty capacitors, and, such. And, those black beuty caps are just itching to blow.
I agree with reforming not being a good idea. It won't last. I have tried reforming caps in many sets. Every time they all failed within a short time.If you are not going to do it right, don't even bother. The only right thing to do is a total proper re build..I have been in repair business much of my life, and, made many mistakes. I have definately found the only way to do it is the right way....
See my post on my replacement for the family tv.
The original owner kept it going through the early 70's with one jury rig after another until enough parts failed that the tv just gave up the ghost.
I'm close to having it done, but, only after much very hard work.
I now have hv, a white line, was getting a popping under the chassis, and, reception.
I just found one reason for the popping, and, fixed that.....
When I got the set it had all bad caps, dead electrolytics, burned resistors, open vert. osc. transformer, bad flyback due to them putting in a 10A fuse in hv to try to stop fuse blowing caused by a shorted horizontal output tube.
I have also had to replace the deflection yoke,14 out of 21 tubes, and, their dead replacement picture tube. I tried proper rejuv. of that, but, it was just too far gone. I suspect the bad caps had something to do with that.
They did dammage the tone control.

Now, are you still sure it isn't so important to do a thoruough job??????
Bill Cahill

And, no matter what you think, that would be all of them. All the symptoms you show would be caused by the faulty capacitors, and, such. And, those black beuty caps are just itching to blow.
I agree with reforming not being a good idea. It won't last. ...
See my post on my replacement for the family tv. The original owner kept it going through the early 70's with one jury rig after another until enough parts failed that the tv just gave up the ghost. I'm close to having it done, but, only after much very hard work. ... Now, are you still sure it isn't so important to do a thoruough job??????


Hi Bill, I think, it is a question of the own philosophy. In the past, I have recapped all black beauties and waxies in old tv sets. "Old" here means sets of the 1950's. Tv sets from the 1940's do not exist in Germany. But a recapped chassis is an ugly look. Who wants a tv set with a recapped chassis? I believe, if you have the choice to select between two same tv sets, one in non-working condition and an untouched chassis, and another one with a recapped chassis in working condition: which one would you prefer?

If there is a necessary for recapping, I would prefer here a procedure like Steve McVoy suggested in his restoration philosophy for prewar sets:

http://www.earlytelevision.org/working_condition.html

My aim is to keep the original look as far as possible.

Some thoughts, why: I believe that none of these sets might be operable in 100 or 200 years. Lack, plastic and isolation materials might dry out, become leaky and lose their properties. Tubes lose their vacuum. Flybacks become porous. We can see (here in Germany) that caps which were reliable in the 1970s and 1980s now become bad one for another.

What would you think when you imagine that many vintage tv sets survived in 200 years, but none of them in original shape? So, with every historical tv set, you have to made a decision: should I repair it or not? Sometimes, it is of more value to keep an old set unfixed as it is than to bring it back to operational condition.

I know that old caps are a risk. I desolder one end of the usual suspects and test them with high voltage (500v or 1,000v), so I can see whether they fail or not. If they test good, I keep them. Aside from this, most of the caps with a parallel resistor are reliable.

Working condition for me means that I keep old tv sets as original as possible. Repairs are done which are necessary for short operating times (for demonstrations or checks). When I operate such an old set, I do it with a variac. I increase the voltage slowly so the caps were not higher loaded than with full power.

Regarding the RCA 9t-246: according to the schematics for the KCS38-chassis, the horizontal output current should be 110mA. The actual current is maximum 50 to 60mA. The 6BG6 is weak. I will replace it when I get a replacement.

Here are two recent screenshots (no recapping and with weak 6BG6!):

http://bs.cyty.com/menschen/e-etzold/archiv/TV/rca/img/RCA_9T-246_inBetrieb1.jpg

http://bs.cyty.com/menschen/e-etzold/archiv/TV/rca/img/RCA_9T-246_inBetrieb2.jpg

The bluish tint of the screen might depend on the phosphors.

- Eckhard

Hi Bill, I think, it is a question of the own philosophy. In the past, I have recapped all black beauties and waxies in old tv sets. "Old" here means sets of the 1950's. Tv sets from the 1940's do not exist in Germany. But a recapped chassis is an ugly look. Who wants a tv set with a recapped chassis? I believe, if you have the choice to select between two same tv sets, one in non-working condition and an untouched chassis, and another one with a recapped chassis in working condition: which one would you prefer?

If there is a necessary for recapping, I would prefer here a procedure like Steve McVoy suggested in his restoration philosophy for prewar sets:

http://www.earlytelevision.org/working_condition.html

My aim is to keep the original look as far as possible.

Some thoughts, why: I believe that none of these sets might be operable in 100 or 200 years. Lack, plastic and isolation materials might dry out, become leaky and lose their properties. Tubes lose their vacuum. Flybacks become porous. We can see (here in Germany) that caps which were reliable in the 1970s and 1980s now become bad one for another.

What would you think when you imagine that many vintage tv sets survived in 200 years, but none of them in original shape? So, with every historical tv set, you have to made a decision: should I repair it or not? Sometimes, it is of more value to keep an old set unfixed as it is than to bring it back to operational condition.

I know that old caps are a risk. I desolder one end of the usual suspects and test them with high voltage (500v or 1,000v), so I can see whether they fail or not. If they test good, I keep them. Aside from this, most of the caps with a parallel resistor are reliable.

Working condition for me means that I keep old tv sets as original as possible. Repairs are done which are necessary for short operating times (for demonstrations or checks). When I operate such an old set, I do it with a variac. I increase the voltage slowly so the caps were not higher loaded than with full power.

Regarding the RCA 9t-246: according to the schematics for the KCS38-chassis, the horizontal output current should be 110mA. The actual current is maximum 50 to 60mA. The 6BG6 is weak. I will replace it when I get a replacement.

Here are two recent screenshots (no recapping and with weak 6BG6!):

http://bs.cyty.com/menschen/e-etzold/archiv/TV/rca/img/RCA_9T-246_inBetrieb1.jpg

http://bs.cyty.com/menschen/e-etzold/archiv/TV/rca/img/RCA_9T-246_inBetrieb2.jpg

The bluish tint of the screen might depend on the phosphors.

- Eckhard
This site sells restuffed paper caps.
http://tubes_tubes_tubes.tripod.com/id101.html

This site sells restuffed paper caps.
http://tubes_tubes_tubes.tripod.com/id101.html

Thank you for this hint. This is a very interesting offer. I have asked there how they restuff the paper caps and wait for their reply.

- Eckhard

Hi to all.

meanwhile I have got a new 6BG6-G. With it I get full horizontal current and full EHT.

After 10 minutes, the horizontal synchronisation run out of control. And the picture became brighter and brighter.

I had to replace the following caps:

In the oscillator: the leaky caps C155 (22 nF), C157 (220 nF). Where I made replacenemts, I kept the old caps in the set and cut only one end of them. The new caps were inserted, so everyone can easily remove the new ones and restore the chassis to its former condition. R179 (100 K) was out of tolerance. Additional, I have replaced C161 (22 nF) due to its electrical loading.

In the D.C. restoration part of the video circuit: C130 (47 nF).

The set is working now without faults. The 10BP4A is tested with 0.4 mA.

- Eckhard