ruffrecords
Well-known member
I am not sure the output stage bias circuit will work unless the transformer primary has some significant dcr. The grid needs to be negative wrt the cathode.
Cheers
Ian
Cheers
Ian
Cheers
Ian
Cheers
Ian
Solid state current sources or gyrators for the cascode and the follower then?I'm a little concerned with so much iron in the signal path, though.
Agreed. I've always considered parafeed an economically-challenged solution.A lundahl trafo is cheaper than a big ass choke and cap + parafeed trafo.
Is it really an issue? The cathode will swing negative due to magnetic storage.With the E81L biased for 20mA that's only 7V on the cathode. Your 200H chokes, albeit you don't need 200H here, have a much higher dcr which puts the cathode at a nice 50V or so.
Yes.Solid state current sources or gyrators for the cascode and the follower then?
No input xfmr either; use a THAT 1510. Arrff!No output transformer.
Indeed. 7V is probably not enough. Adding a cathode resistor (by-passed or not) may solve the issue. Or find a way to apply fixed negative bias.I am not sure the output stage bias circuit will work unless the transformer primary has some significant dcr. The grid needs to be negative wrt the cathode.
I'm not neglecting the advantages of parafeed, but I think a SE xfmr can be made for a lesser cost than a choke+xfmr combo for equivalent results.
Of course, I can be completely wrong, since I have ceased using valves and xfmrs long since...
Indeed. 7V is probably not enough. Adding a cathode resistor (by-passed or not) may solve the issue. Or find a way to apply fixed negative bias.
I looked at the E81L datasheet. For 20mA at 200V, Rk is only 120ohms. For 15mA, 180 ohms.Yep, total primary dcr of that transformer, with all windings in series, is only 352R
With the E81L biased for 20mA that's only 7V on the cathode.
Chokes, even the audio ones, used RF winding techniques (honeycomb, fractioned...)If you're going parafeed, I think you need to commit and buy a proper anode choke.
Apart from a few MHz for FM, aircraft and DAB, almost everything below 0.5GHz has been given over to amateur radio. They probably make their ownChokes, even the audio ones, used RF winding techniques (honeycomb, fractioned...)
Is there anybody left doing them?
I looked at the E81L datasheet. For 20mA at 200V, Rk is only 120ohms. For 15mA, 180 ohms.
With 7V, it is nearly at cut-off.
I believe with 350 ohms, it would idle at about 11mA.
Correct me if I'm wrong.
Chokes, even the audio ones, used RF winding techniques (honeycomb, fractioned...)
Is there anybody left doing them?
Why? You don't need voltage across a xfmr for it to work. You need current. In what is it different than putting the same xfmr in the anode?the output transformer doesn't really have enough DCR to work into.
That's my feeling too...Apart from a few MHz for FM, aircraft and DAB, almost everything below 0.5GHz has been given over to amateur radio. They probably make their own
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