Early RCA Horizontal Circuitry...Help!

[Chris K]

I guess what I'm looking for is some education regarding the horizontal circuitry in the KCS 47 and what all these things do and how they do it. In this one circuit there's a horizontal frequency, horizontal drive, horizontal waveform, horizontal linearity and width adjustments plus the horizontal hold control not shown here. So the 6SN7 puts out the oscillating frequency that's tuned to 15.75 Kc by the adjustable coil for horizontal frequency. That's a sawtooth shaped wave right? It's modified to a double peaked wave where the waveform adjustment lets you tune that shape to where those two peaks are of equal amplitude correct? I guess I'll stop there and try to figure out how this all happens and why. I know only very, very basic vacuum tube operating theory. The tube produces the oscillating waveform that comes out as a sawtooth. The oscillation comes out of the plate, goes through the coil and back to the screen to do what, set the on/off timing of the screen gating the electrons from the cathode to the plate? What is the 180pF capacitor doing for this? I guess what I'm asking is how does this loop produce the 15.75Kc oscillating frequency and keep it stable???

Really admitting my ignorance here but, believe it or not, I am a scientist/biologist professor and I need to know how things work at the most basic origins. Electricity absolutely baffles me. It took a lot of explaining to get me to understand how AC works when there's no net movement of electrons in the wire!!!!!

[Kevin Kuehn]

Oh boy. Short answer is any oscillator is a tuned circuit and requires feedback. The 180pf provides some feedback from the tubes plate circuit to the grid circuit. The adjustments are, for the most part, self evident as they are named, they do as implied.

As far as theory of operation you may be best off reading a service text from the period of the set you're working on. I agree it's really difficult to understand these circuits without building from a very basic and fundamental understanding of circuit concepts. To jump in feet first trying to understand TV circuits, is about impossible. For TV specifics I'll recommend Grob Basic Television 1st or 2nd edition, and Milton Kiver Television and FM receiver servicing 1st-4th editions should be fine. But if for instance you don't have a firm grasp of Ohms law and how voltage division happens in both DC and AC circuits, even these basic TV books will be difficult to understand. Honestly you need to be seriously interested, dedicated, and self driven to learn any electrons theory.

[Chris K]

I actually have those texts among others from the era. I do understand Ohms law and DC circuitry to an extent. What do you mean by voltage division? That sounds simple enough but I'm sure there's more to it than that! DC circuitry is easier for me because it's directional and flowing. What is the oscillating frequency coming out of the oscillator?

[Kevin Kuehn]

By voltage division, I mean how the various electrical and electronic components react to both AC and DC current, and how voltage influences current flow. A starting point is to understand how to calculate DC voltage drops across both series and parallel resistances. Once you can do that you can at least follow how the power supplies divide voltage and distribute power to the various circuits.

[Chris K]

Originally Posted by Kevin Kuehn

By voltage division, I mean how the various electrical and electronic components react to both AC and DC current, and how voltage influences current flow. A starting point is to understand how to calculate DC voltage drops across both series and parallel resistances. Once you can do that you can at least follow how the power supplies divide voltage and distribute power to the various circuits.

Do you mean the additive effect of resistors in series vs the overall resistance in a parallel circuit being a value between the hi and low resistor values? I think I understand that however getting parallel resistance right when you're trying to get a resistance value for a resistor you don't have is a bit harder. I use the online calculators and an educated guess then go by some trial and error to get close enough. Is this what you mean Kevin?

[Kevin Kuehn]

Originally Posted by Chris K

Do you mean the additive effect of resistors in series vs the overall resistance in a parallel circuit being a value between the hi and low resistor values? I think I understand that however getting parallel resistance right when you're trying to get a resistance value for a resistor you don't have is a bit harder. I use the online calculators and an educated guess then go by some trial and error to get close enough. Is this what you mean Kevin?

Yes but also how the voltage across, and current through, is calculated. But you have the first part.

[Chris K]

I'll stop this soon because VK is no place for electrical theory. I get the hydraulic analogy where V=Pressure, I=Current (amps) and R=resistance or constriction in flow. So if voltage is overall pressure on one side of the divider and coming out of a rectifier tube at 300V DC at 2.0 amps and it encounters parallel resistors one at 1K and the second at 500 ohms, obviously more current will flow through the 500 ohm than the 1K. But I don't see how you calculate the voltage in the 2 circuits after the resistors unless I'm thinking about the mathematics of this all wrong.

[Kevin Kuehn]

As you say, across two parallel resistors the current divides between them, but the voltage drop across any parallel combination is the same. In your analogy you could define the voltage from the rectifier as a constant, and the current draw from the supply is subject to change dependent on the total resistance load. When you combine multiple parallel loads in series they each form their own voltage drop according.

[Chris K]

OK got that. Back to my horizontal circuit, specifically the width control and how it influences the horizontal deflection. The yoke is a big electromagnet that bends the electron beam scan using the horizontal windings to deflect the electrons side to side. The vertical yoke when electrified and magnetized determines where the scan starts positionally at the top of the phosphor screen and where it finishes on the bottom. Does the width control, as a variable resistor, potentiate the voltage to the horizontal yoke windings and is deflection left to right dependent on the strength of the voltage induced magnetic strength? It doesn't look to me like it's directly connected (I'll post a better picture tonight) to anything going to the yoke. I understand the role of the permanent magnets, ion traps and electromagnetic focus coils in other TVs providing additional nudges to the beam.

[Kevin Kuehn]

The forum has been so flaky I can hardly get a post in today.

That width control appears to be varying the screen voltage of the Horizontal output tube, and probably determines how long it conducts for the right portion of the scan.

[Chris K]

Same here....Service Unavailable

[Kevin Kuehn]

It also adjusts the B+ going the the horizontal hold control. It's not a conventional circuit because of the direct drive yoke configuration.

On my KCS40 chassis they actually do have the resistive width control in series with the horizontal yoke winding. Same basic direct drive circuit, but more than one way to skin a cat!

[Chris K]

Originally Posted by Kevin Kuehn

It also adjusts the B+ going the the horizontal hold control. It's not a conventional circuit because of the direct drive yoke configuration.

On my KCS40 chassis they actually do have the resistive width control in series with the horizontal yoke winding. Same basic direct drive circuit, but more than one way to skin a cat!

Direct drive yoke?

This site is very unstable today like you said. I hope we're not on the verge of another crash.

[kf4rca]

More on the synchroguide circuit here:
http://rca.vobj.org/RCA%20Engineer/R...ignHistory.pdf

[Kevin Kuehn]

Originally Posted by Chris K

Direct drive yoke?

The horizontal yoke winding is directly driven by the plate circuit of the horizontal output using that odd looking air core auto-transformer. Conventional flyback transformers up to that point used a isolated secondary winding.