1950s RCA B & W TV

[Captainclock]

Hello everyone today I've been tasked with repairing a 1950s vintage 14" B & W TV for a neighbor and it works perfectly except for the vertical stage, the bottom of the screen is not all the way to the bottom of the screen, and the top of the screen is stretched so that people's heads look like they're larger they they really are. Any ideas as to what would be causing that issue? it has seperate vertical amp and output tubes, which I'm thinking one of them might be bad possibly, but not sure. Its a cold chassis set, with VHF Only. I have some pictures I'll post of the set.

[dieseljeep]

Originally Posted by Captainclock

Hello everyone today I've been tasked with repairing a 1950s vintage 14" B & W TV for a neighbor and it works perfectly except for the vertical stage, the bottom of the screen is not all the way to the bottom of the screen, and the top of the screen is stretched so that people's heads look like they're larger they they really are. Any ideas as to what would be causing that issue? it has seperate vertical amp and output tubes, which I'm thinking one of them might be bad possibly, but not sure. Its a cold chassis set, with VHF Only. I have some pictures I'll post of the set.

You might get lucky and the tubes might make it a little better, but problems like that in an RCA are generally a capacitor problem. They're on the side mounted PC board.

[Captainclock]

Originally Posted by dieseljeep

You might get lucky and the tubes might make it a little better, but problems like that in an RCA are generally a capacitor problem. They're on the side mounted PC board.

I noticed that it has only 7 paper caps on the PC Board and the rest are mylar type capacitors, and then on the back on the chassis (the metal part) theres several paper capacitors.

[Eric H]

Even on their best day these RCA's don't have the best vertical, bad capacitors, drifted resistors and probably a rotted yoke cover just make it all the worse.

[Electronic M]

Vertical recap including/especially the output cathode lytic seems necessary. When I fix an RCA of that era for someone I don't let it leave my bench without a full recap (cause I know I'll get a call back when a vintage cap soon lets go).

[jr_tech]

I had a similar looking, but series string version of the set, and it did not use a cap in the cathode circuit of the 6AQ5 vertical output tube (cath was grounded). The problem cap was a .022 uf cap connected to the grid of the vertical output... I went ahead and changed all of the caps in the vertical circuit anyway. Somewhat difficult to get the pc board out, IIRC, think I "j hooked" the caps.

jr

[Captainclock]

Alright I'll see what I can do. it doesn't help matters that some of the capacitors on the PC Board are of the "Bumblebee" Variety which means I'm gonna have to figure out what the stripe patterns mean on each of the capacitors. The rest of the capacitors have the value written on the case so I'll have no problems there.

[Electronic M]

Ever see a modern replacement cap with a 3 digit value referenced to pF? For instance a 332k cap is 3300pF=.0033uF or a 104k cap is .1uF=10,000pF. Bumblebees use that same modern notation only the numbers are encoded in resistor color code (there are also usually extra bands for tolerance and voltage)....IMHO if you are using modern caps with that notation and know color code, bees are easier to change than other styles since you can read the number off the color code and then grab that number out of the replacement parts bin.

[jr_tech]

This might help:

https://imgv2-2-f.scribdassets.com/i...471/1455831005

jr

[Captainclock]

Originally Posted by Electronic M

Ever see a modern replacement cap with a 3 digit value referenced to pF? For instance a 332k cap is 3300pF=.0033uF or a 104k cap is .1uF=10,000pF. Bumblebees use that same modern notation only the numbers are encoded in resistor color code (there are also usually extra bands for tolerance and voltage)....IMHO if you are using modern caps with that notation and know color code, bees are easier to change than other styles since you can read the number off the color code and then grab that number out of the replacement parts bin.

Now what's interesting about these Bumblebee caps is that they are of the radial leaded type that sit upright on the board as opposed to the axial leaded type that you normally see.

[Captainclock]

Originally Posted by jr_tech

This might help:

https://imgv2-2-f.scribdassets.com/i...471/1455831005

jr

Thanks for the link, that was very helpful.

[Electronic M]

Originally Posted by Captainclock

Now what's interesting about these Bumblebee caps is that they are of the radial leaded type that sit upright on the board as opposed to the axial leaded type that you normally see.

I've seen and replaced both. They both have the same color coding scheme.

[Captainclock]

Originally Posted by Electronic M

I've seen and replaced both. They both have the same color coding scheme.

OK, well that's good to know because this is the first time I've ever come across a radial leaded Bumblebee capacitor, I've seen the axial leaded ones plenty of times before in old radios but never a radial leaded one.

[Eric H]

You can still use the axial caps to replace them, just bend one lead over so they both stick out the same end and stick it on the board.

You have to remove the metal shield from the bottom of the board to do the soldering, it's not all that hard, five or six screws around the edge, possibly a trimmer cap soldered to the shield and the shield soldered to the board in three or four places, a lot of stuff but not hard to get to. It's actually a bit more difficult to figure out how to maneuver the shield out around the wires.

As I mentioned, the vertical on these is pretty fussy so check all the resistors in the vertical circuit and replace any that are more than 10% off. Use care with the soldering iron, the traces on the board are flimsy and will peel off easily if they get to hot (or even if they don't).

I just finished up a similar set but series string and 17" tube, I never did get the vertical perfect, just good enough that you don't notice any imperfections unless you have a test pattern on.

[Captainclock]

Originally Posted by Eric H

You can still use the axial caps to replace them, just bend one lead over so they both stick out the same end and stick it on the board.

You have to remove the metal shield from the bottom of the board to do the soldering, it's not all that hard, five or six screws around the edge, possibly a trimmer cap soldered to the shield and the shield soldered to the board in three or four places, a lot of stuff but not hard to get to. It's actually a bit more difficult to figure out how to maneuver the shield out around the wires.

As I mentioned, the vertical on these is pretty fussy so check all the resistors in the vertical circuit and replace any that are more than 10% off. Use care with the soldering iron, the traces on the board are flimsy and will peel off easily if they get to hot (or even if they don't).

I just finished up a similar set but series string and 17" tube, I never did get the vertical perfect, just good enough that you don't notice any imperfections unless you have a test pattern on.

Yeah, I kind of figured as much about the circuit traces being easily lifted, as it was the same way with my 1957 GE 9" TV, when I went to replace the capacitors on the PC Board on that TV a couple of the Circuit traces lifted at the holes where the capacitors go through and attach to the board, thankfully they stayed attached to the board well enough to keep the circuit intact, I'm guessing that since this TV uses a seperate tube for the Vertical amplifer stage vs. the Vertical output stage, that means that the vertical circuit capacitors are going to be in two different areas of the board?