Super spud-amp?

[JoshK]

I was thinking about Gary Pimm's pentode +CCS driver circuit last night and it occured to me that this could potentially make a super spud, could it not? I think that would be a cool project to learn some things on, specifically how to build the CCS and how to set it all up.

The small Edcors are cheap so the project wouldn't need to be expensive. One could also use the Swenson/Pimm regulator for the B+ and learn how to build that too. Then it would be an uber spud.

If I did my calculations correctly you could use a 2.5K/8 ohm OPT, since the circuit has a Z out of 500, and get 3 1/4 watts rms out. That is 2A3 territory from a spud. Might make for a kick *** compression driver amp for my active speaker project.

What do you guys think? Would it work?

[JoshK]

Oh forgot to add the link

http://www.pacifier.com/~gpimm/drivers.htm

Specifically the driver circuit on the right of the top schematic (using 6BQ5).



I was also thinking that this would mean parafeed is in order.

[dsavitsk]

I don't think I understand the circuit. Isn't that a CCS on top of a CCS? Won't they fight?

[Wavebourn]

Yes, they will fight.

Try this approach:



FET for top transistor will give you higher dynamic resistance.

[rdf]

I'm not seeing it, where is the second CCS? The bottom pentode looks to me a simple R biased gain stage with a resistive plate load to set gain/distortion.

[dsavitsk]

Originally posted by rdf
I'm not seeing it, where is the second CCS? The bottom pentode looks to me a simple R biased gain stage with a resistive plate load to set gain/distortion.

The one on the left, the plate load looks like a resistor to me (and I don't understand the CCS there at all -- maybe I'll go read the article).

But, for the one on the right, I thought the point of a pentode in this configuration is that it is more or less a current sink. Looking at pentode curves, as G1 changes with signal, the current draw should change, and it looks like the voltage is incidental, which will be trouble if the CCS won't allow this to happen. Maybe there are imperfections which lead to huge V swings? Anyway, I really don't understand pentodes very well, so I'm trying to ask a dumb question to see if something will click in my head.

Edit: From the article

Here are the results of some Pentode driver stage experiments done awhile back. The idea was to see what could be done combining Pentodes and CCS's. Generally, you can't load a Pentode with a CCS as you are effectively trying to series couple 2 CCS's. This issue is resolved by having a plate resistor in circuit so there is a defined resistance that the Pentode and CCS can work into.

I didn't notice that resistor to ground on the right

[rdf]

The only reason it stood out are sims I'm currently doing on a DC coupled, plate choke loaded pentode driver config. Stage gain is set by shunting the choke with a series RC sting.

In both circuits my guess is the top CCS provides the bulk of the gain stage static current and allows more leeway in selecting the shunt R & B+. I haven't tried the circuit on the right but the one left never sim'd with acceptable stability. In the sense that both circuits can be seen as a voltage to current gain stage in series with an essentially infinite DC impedance, it has similarities to two series CCSs.

It also looks like in both these circuits the real purpose is making use of the CCS mu function.