parafeed - Gyrator vs CCS anode load

[adamus]

Hello all.

I am currently messing around with parafeed headamps.

Does anyone have any comments regarding the difference in sonics between a gyrator and a CCS load?

CCS load is cascode pnp with led Vrefs (morgan jones).

I could knock up a gyrator, i think i have a couple of dn2450 and a variety of film caps. Anyone have a prefered schematic?

Thanks

adam.

[bigwill]

Gyrators are great because you can manually set the quiescent anode voltage, and you set the current with the usual cathode resistor (or LEDs if you're cool). No worrying about adjusting a CCS, the valve will draw what it wants

[Hearinspace]

I don't whether it will fit your needs in this case but Wavebourn's SVCS is a beautiful thing.
It's mentioned a few places on the site. Search SVCS

[adamus]

Thanks for the link. I should add this is fed by a salas shunt supply, so I have a nice clean supply. Could I get by with a single dn2450 or is more sand required. Afraid I am a follower here so advice welcome.

[Wavebourn]

You can probably be fine with a single dn2450; all depends on which tube in which regime do you use, and which load does it drive.

In short, gyrator load on AC is identical to CCS, but on DC is not. Similarly to a choke, but not exactly.

[adamus]

C3g cap coupled to a 10k edcor.I have been playing with operating points and 14 ma , 190v plate seems to sound best.

[Wavebourn]

I can't find data on dn2450...

[adamus]

Ooops.... try dn2540n5 http://www.supertex.com/pdf/datasheets/DN2540.pdf

sorry for the typo

[Wavebourn]

Ok, thanks!

It looks like you need 50V swing. That means, something like about 40V voltage drop on gyrator is fine. Output capacitance will be still low on max swing, and power dissipation about 0.5W that is fine without heatsink. 230-250V B+ will be needed.

I would use it with something like 360 Ohm in source, for 5V voltage drop. That means 5-1=4V between gate and source. If to use 470K trimmer to set anode voltage and 2.2 megaohm between gate and drain, you have plenty of headroom to trim working point for your tube.

Here is the example, but using BSP225 enhancement mode MOSFET that required different values of resistors (C3 should be 4-10 times higher, actually):

http://wavebourn.com/forum/download.php?id=493&f=7

[Bigun]

Nice design Wavebourn.

I'm curious (still learning, as ever), why did you opt for a tube (V2) as buffer to drive output tube if you allow sand in the game you could also use a source follower ? or even use another gyrator for the cathode load for V2 ?