audio-talk

Ok, so first step, pick a valve. Then you need to pick a operating point. Both of the valves you have chosen have suggested op points. But the first thing I would do is take the valve of choice and draw the max power curve on the graph. However the 27 doesn't seem to tell us that. So, it does state ...

Max N wrote:Actually, even the simple cap to ground makes my head hurt now, so I think after all that I may take the really easy way out and go with 5687 for the cathode followers.......

Yep, that works

Maybe not. but you make another point, g2 isn't just a resistive load. I still think the simple cap to gnd stands the less chance of my head exploding

Yes, thats what I was badly saying. There will be current through the cap, the current is used to alter the voltage across the resistor between B+ and g2, so as you say thats the load the cathode is driving into. So you are driving g2 via a high pass filter formed by the cap driving the resistor in ...

Yep, what put me off the true pentode connection was the cathode having to drag both the 211 grid and push charge into and pull it out to keep the cap to g2 going. Can't help thinking a zener may be better as a level shifter. Thats what I did with the 813 g2. http://www.t-linespeakers.org/tubes/trio...

Where shall i go next? What can I do with these newly honed powers of maths and 2 triangles full of SI units? DTB Phono Stage :?: Or maybe a common cathode amplifier stage. Start with valve and B+, pick an op point, decide on a anode resistor, then pick the cathode resistor, calculate the size of b...

Well, I don't know for certain if thats the correct number, but it certainly should be by the maths. It does depend on if the gain is correctly reported. You can estimate that from the curves as well, MJ goes into how to find all three values from the curves, but I will leave looking that up as an e...

Ok, first off, it may be that the curves look less than linear but it sounds great. I have heard 6080 used as a SET and it seemed to sound great, so don;t jump to conclusions. Second. Don't be fooled into thinking that the bit where they are straight is the linear bit. What that means is the ra and ...

Yep, thats good, though the chart would indicate that that point woulr need -24v on the grid, not the -18v mentioned before. But other than that, yep fine. Just found this on xkcd "Warning: this comic occasionally contains strong language (which may be unsuitable for children), unusual humor (w...

Yes, except g2 is connected to 0v through a cap, and the cathode goes to a -ve supply, but other than that just the same.

It might be hard to get a linear class A point from that valve, looks like its designed for class C use.

Whahoo! Your perseverance is paying off:) I had a thought on the way in, these are MAX parameters aren't they? That O.P. also puts us in the bendy curvy zone doesn't it? Could I pick a more linear, I think thats the word, O.P. and then draw a Tangent (get me!) point? Sleepy of Dartford. DTB You can...

Do you mean g2 or g3? g3 is connected to the cathode, and g3 is referenced to the cathode if its a pentode. Its a bit tricky, I connected g3 to the cathode, but the question is what to do with g2. To be a pentode, the voltage between g2 and the cathode should remain constant, but for that to happen ...

Yedp, thats it, I just went until the 500v so at least one part was exact (ish) You can also pick any point for the lower value, just subtract the lower current value from the upper one to find the "distance" in ma in the same way as you are doing with the voltage. This might help http://e...

I thought I'd cracked it for minute and could just use the ohms law triangle 250V/0.025A to give me the ra but it works out as 10K Ohm Just to fill in hy that didn't work. What you have done there is calculate the static resistance, and the reason you get a different number is its going through the...