overall a neat design.... yet even with it's as drawn simplicity... it could loan itself to further experimentation.

cheers,

msl

Experimentation is also good. Any curcuit could loan itself to further experimentation, it is in large part why we're here.

What property or performance parameter were you improving by changing the cathode load from a low Z LED to a hi-Z choke? Also, what would the DCR of this choke be? and a final follow up, how would said parameter change?
cheers,
Douglas

I'm not 100% sure I understand your question. let me give it a shot.

If your asking how difficult would it be to implement say a plate choke on top of the anode of the 5687... answer is (imo) simpler and moreso straightforward than the CCS. Just two wires to hook up. You would need to double check your voltage drop across the plate choke and make sure you get the target plate volts on the anode.

re: output impedances see Damir's response. What you would want to aim toward is a minimum of 100 henries imo.

all very doable and straightforward. Some folks (though not all) favor the sonics of choke loading the plate vis-a-vis a CCS. On paper the CCS is technically a better solution. It offers much, much higher AC impedance than a plate choke. So... it one of those subjective areas... try both and see which sounds better to you.

a high L choke can be substituted for the output resistor.... the claimed advantage here is that the choke offers relatively high AC impedance and less dc resistance than the resistor. Here you want to spec in a very large L for the AC choke. Say a thousand henries min.
Again... by the numbers alone the resistor offers a greater ac impedance (1 meg in this case)... but it also has 1 meg of dc resistance. A 1000 henry AC choke would have approx 125,000 ohms of impedance at 20 hertz... while only having say a thousand to four or five thousand ohms of dc resistance....

again, I think it's another of the instances of you've got to try it for yourself and "hear out" any differences and which sounds better.

all of my suggestions\ideas were offered only as alternate ideas\strategies. the guinevere looks pretty neat as drawn up and is even as drawn up still a doable, practical, rather straightforward line level amp.

cheers,

msl

I do wish to have an answer from the starter of this thread on the output impedance change. Maybe he didn't realize how the CCS works.

I would like to see some good plate load choke circuits. Unfortunately for a reasonable output Z, there is another stage required, or one takes the hit on drive capability.

Also, a more general Question: has anybody actually looked at the actual impedance provided by an anode choke? The capacitances from the winding-winding interaction usually give a self-resonance that is too low for my taste. There is no further increase in realized impedance after self resonance, so the choke does not really behave as an infinite load anymore.

With chokes, I have found that sonics improve with linearizing the inductive response. The easiest way to do this is with a gap in the stack. A non-linear load provided by a choke at LF, where its reactive and nearly round loadline is nearly equal to plate Z just does not make any reasonable sense to me. Yet!

I suspect this is a large part of what bugs me about a lot of SE amps I've heard. Take a 2A3 working into a 2k5 load. Textbook no? Primary L? let's say 10H. Omega*L at 20 cps is 1256 Ohms. That's going to be a squiggly mess at LF. Not to mention being more than a bit down on power delivery ability. It's -3dB point won't even come until 40 cps, where the reflected impedance equals the reactive one, and then we'll still be presenting the 2A3 with a load of 1k2( two 2k5 in parallel ). This sort of thing isn't going to start looking OK( let alone good ) until a few more octaves have passed under the bridge.

Absolutely room for some experimentation with inductive loads I always say. Just realize how they are working and figure a way to keep the less-than-ideal perfomance from becoming visible. But that's how we work anyway, no?

If there was such a thing as my hypothetical SE2A3 OpTx, I'd really like to know how to keep its shortcommings out of sight....
cheers,
Douglas

he covers a lot of it pretty well.
cheers,
Douglas

• inductive load line