What is the 75ohm "dotted" connection to ground at the input?

That means that the circuit is designed for a 75 ohm input 1 volt video source (standard).

Thinking of a transistor as a tube* is a really conceptually poor design approach. A BJT is completely different in behavior/operation from a tube. A tube is a voltage amplifier and a transistor is a current amplifier. Assuming DC biases are correct and can be ignored and AC analysis of a transistor looks like a relatively low resistance resistor that measures input current and controls a current source based on the current through the resistor. A tube looks like a near infinite resistance the voltage across which controls a variable voltage source.

*Except for FET transistors which are functionally and behaviorally identical to triode tubes.

Ok.... so it's not an actual part, just a way of noting (in dummy terms) "video is supposed to go there" :thmbsp:

You probably want to actually install the 75 ohm resistor, so that your DVD player or other source is seeing the proper load impedance.

The exception would be if multiple inputs are "daisy chained" from a single video source. Then you install the 75 ohm terminator across the last input in the chain.

Transmission line theory 101 terminate your line with it's characteristic impedance to prevent reflections, ringing, reduced signal at terminals etc...Might be a good idea to brush up on (or look up the basics of) transmission line theory. If you are ever running a wired signal more than a few feet (especially if it is more than a tiny fraction of wavelength), or transmitting, T-line theory is crucial.

Question.
 

What is the polarity at the CRT? Are you looking at the schematic or a scope?
The CRT should be positive. Which means the driver tube input should be negative.
The output of the detector is usually negative, because it is transmitted that way. (Sync is peak power.)
Some of those detector circuits produce 5V of video.

There is no fixed polarity that MUST be sent to a CRT. The polarity of video you feed a CRT depends on whether it is cathode injected video or grid injected video....Both injection schemes were used back in the day*, and those 2 schemes want the opposite polarity of each other.

*In fact color sets used both at once to effectively mix the color difference and monochrome signals into RGB in the electron gun to save a few signal tubes in the design.

The output of the detector is positive on this set. The video is amplified once and then fed to the grid of the kinescope.

Progress! I've got output with the correct polarity using that circuit. I'll have to do some tweaking, but it's a victory for now. One question, is there a way to adjust gain in that circuit?

1) Please tell me you are not using the circuit with the emitter tied directly to ground instead of through a resistor.
2)Are you using the collector output (which is inverted)? In that case, the gain is equal to the ratio of the collector resistor divided by the emitter resistor. Without the emitter resistor, the gain is very non-linear and depends on the amount of current in the transistor, which varies the effective emitter impedance. So, to get the gain you want, divide the collector resistor by the gain needed and use that value for the emitter resistor.
3) a fine point to add: if the following circuit (connected to the collector) has a high impedance (like a tube grid), all is well, but if it has a lower impedance, closer to the collector resistor, it will reduce the gain because it reduces the total effective resistance at the collector.

Well to tell you the truth, I built a number of projects back in the day (late 50s to early 60s) using the common emitter configuration with no resistor in the emitter-to-ground leg. They worked fine with no nonlinearity problems etc. But these were all done with germanium transistors. Apparently that does not transfer well to later practice with silicon transistors. So I was 'waay behind the curve and gave crappy advice and should be duly reprimanded. :bash:

So by all means sub some resistances in the emitter leg per the more experienced advice given.

(In the early days of transistors the "triode" analogy was indeed used as a visualization aid for newcomers. For the purpose at hand, it disregarded the input-impedance disparity. Then when FETs finally came along, the input impedance truly mimicked a vacuum triode.)

A common deliberate use for the variable emitter impedance is in an IF stage with Automatic Gain Control (AGC). Even then, an emitter resistor is generally used, but the emitter also has an AC bypass capacitor directly to ground. The AGC feedback voltage is applied to the base of the transistor to vary the current in the transistor. This works fine as long as the IF signal is small compared to the DC bias, so the signal itself doesn't cause a variation in gain (which results in distortion). So, you may see AGC applied to the early IF stages and not to the last stage.

Because the video you want to amplify (1 volt) is large compared to the base-emitter drop (0.7 volts) it definitely could cause distortion; but when applied to the combination of the base-emitter junction and the emitter resistor, the emitter resistor keeps things linear.

Yeah, the emitter resistor all makes perfect sense now. The stuff I built decades ago was all small-signal devices, and low supply voltage (like 3 to 6 V). I was locked into the 'no emitter resistor' pavlovian habit. Moral of story: Dont be stoompid

I was using the circuit with the emitter tied directly to ground. I will experiment with an emitter resistor next.

By the way I have to say this is really fun to experiment with transistors. I've never done anything with them before...They're a lot smaller than tubes :yes:.