American Circuits

[Nowhere-Man]

I don't like the way that US scheamtics are drawn.

One point which you have hinted at is that the power supplies have negligible impedance. If everything is ideal the anode is at the same SIGNAL potential as the ground or 0V rail. The DC potential is different, that's called HT Or B+ in US speak.

I had another look at it last night. I'm so used to seeing the signal between grid and cathode that the cathode follower had me a bit puzzled.

The way I begin to understand it now is there is mostly one electrode on a tube that forms part of the input and the output as well. I know this will be understood already by most but I'm putting it into my own lingo, so to speak (just to help me clarify my following post). So, with regard to the cathode follower the signal still is directed to the grid but the grid shares this signal with the anode. And the anode also is included in the AF output along with the cathode. Every writer says the anode is "common" to the circuit but that always confused me a bit.

I take the point about 0 reference as I have a couple of car radios that use the chassis as positive ground.

Here is something interesting, though: In cases where a resistor is between cathode and chassis, there is a DC voltage drop. Someone already just explained that correctly. And, yes, one part of the GB resistor is more positive and the chassis part can be used for grid bias. When an AC signal is in series with this resistor it can flow through the DC part of the circuit and create negative feedback. So, the usual 0.1 mF capacitor can be shunted across that same resistor and prevents any AC drop at that part of the circuit. There are one or two diagrams that compare negative feedback circuits with filtered circuits where the AC isn't allowed to influence the resistor drop.

In closing, I note there is a schematic for a Simplex Super X receiver. This had me baffled but I note a few people online have built one. What throws me is the tubes are shown exploded so, for example, the mixer is shown in two halves, upper and lower. The L.O. part of the tube is lower down with all the HT voltages. I really prefer complete diagrams but maybe I can work it all out one rainy day.

It would be fun to build one of these one day.

Tonight I'll have a look at why cathode followers are used and what advantages they offer.