More information on my 6T74 RCA Victor television

[Bill Cahill]

While taking time off from repairs on the set, and, working on a phonograph for a forum friend on ARF, I have been gathering up parts chassis' for my tv.
The latest one, KCS 49A, badly rusted, No cabinet, had a prommissing looking tuner.
I removed it, did a thorough cleaning, cleaned the contacts with a new contact cleaner I bought at the hardware store, and, lubricated the mechanical end of the tuner.
This tuner seems to have alot of primmisse. I see very little to no wear on the contacts, and, it is not scraping.
I plan on installing this tuner in my set.
I'll be back on it in a couple of weeks.
Bill Cahill

[Tube TV]

HI bill ,
I've been gone for a while , is that the RCA that you were having lots of different problems with a few months back ?

[Bill Cahill]

Originally Posted by Tube TV

HI bill ,
I've been gone for a while , is that the RCA that you were having lots of different problems with a few months back ?

Yep. It's been on resurection respirator for over a year, now.
I have to take some time off for a few days to ordr parts for that phonograph, so, I put the tv back up. I'll be replacing the tuner.I had a picture, no sound on one channel here for a couple of days. then, that channel cut out, then, I lost hv again, and, set was making a popping sound, again.........
Bill Cahill

[Tube TV]

You sure have alot of patients .

Is the popping coming from the flyback transformer ? But didn't you already put a NOS flyback in ?
Can you see any sparks when it is popping ?


I know what your going through , I still haven't corrected the troubles that im having with the 56 GE ultravision .
It has some horiziontal oscillator problem , it wont stay on any set frequency .
I question that it was the flyback due to the fact that it had been sitting in a shed with no heat for 20 + years , and thought that moisure could be fouling things up , but the B&K operated the horizontal output and HV fine so I would assume that the probem it in the horizontal osc . or perhaps in the sync ...
I tested the flyback on both the Eico flyback checker , and also had it connected to the B&K television analyst , and had the plate drive in it generating the high voltage .

Done a recap on it and still no success .
No improvement from the first time I plugged it in .
It's to a point of testing each and every resistor in the set , and marking it once it test OK .
I'll have to get in touch with just old radios , they have the schematics for it .

Sounds like your making headway with you RCA , that's great to hear .
Best of luck with it .

[Bill Cahill]

Replace the micas in both the sync, and, horiz. osc. circuits.
They tend to get leaky... Flyback wouldn't cause that problem.
Also, check resistors in same two circuits.
A leaky horiz. osc. tube could also cause that.

Yah. Too many patients on bench.
But, most recently finnished one is my Symphonic stereo.
It plays great.
No, pooping is somewhere in chassis.
I have a new old stock flyback in set. Original failed. Openned up.
I'm also going to try another tuner in set.
The one in it is known bad.
So was original. It worked at first, then, after shipping, only one channel worked, then, it quit.
Until this tuner find, all my tuners have been worn out.
This one I'm putting in is in much better condition....

I'm beginning to wonder if the tuner was causing my sound problem. Does this tuner use a seperate carrier for the sound??
Some tuners do.
Sound I F takes it's initial signal from second video I F, but, the diodes of the 6AV6 is also connected in with the tuner.
If tuner does have a seperate sound carrier, that could very well be my audio problem......
Bill Cahill

[Tube TV]

while it's good to hear that you got a good tuner for it .
You might be right about the tuner causing the your sound problem , seeing as it feeds back into the tuner ..
I had a TV , a philco , if I recall , and before I cleaned the tuner I had to wiggle it back and fourth to get the sound to come in . it was a mid 1960's portable .
Thanks for the advice on those mica's in the sync and horizontal circuits on the GE .
I got to dig into it one of these days .

Im just looking at a schematic for a 1953 RCA 21-D346 .
And I see what you mean by the diodes on th 6AV6 feeding into the tuner .
Do you have a KRK-22A tuner , with a 6X8 oscillator , and a 6BQ7A RF amp ?
On my schmatic , which is for a 1953 , this is for the AGC .
If you need it , I have all the RCA info for the KRK-22A tuner .

[Bill Cahill]

Nope. Yours is much later. Mine is a KRK-8 tuner.
KCS 47-A chassis. 1950
AGC on mine another tube is the rctifier. 6AL5 video Det. doubles as AGC rectifier. That is derriving its' signal from pin 3 of the tuner. The 6AV6 diodes are somehow also getting their negative bias from the same source. Hmm. Only one wire is going to the tuner physically, so, connection must physically be made somewhere else. I want to check that out.
On the cheaper sets the first audio, 6AV6 doubles as AGC rect. On mine, they didn't do it that way.
Don't look in Sam's for it. Look in either Riders' television mannuals, or, the RCA red book. 1950.
Remember, mineis one of the deluxe sets with differences, and, improvements. For instance, on the cheap chassis, they used a simple 6J5 for vert. osc., 12AU7 was sync seperator. No sync amp.
On mine, they used a 6SN7 for vert. oscilator, and, sync amplifier.
On mine, they also had improvements on the video output stage. That's the other 12AU7. It's a slightly different video frequency. They added a capacitor accross a resistor, and, put a small capacitor betwwen center tap, and, high end of contrast control. Gives the set better contrast.
I now know why the family set seemed to have such a nice picture for years. Better circuitry!!!
Well, today, I'll be back on tuner.
Bill Cahill