Do I have this CCS configured correctly? Tube preamp..

[G]

Hi Guys,

While I'm waiting for parts to build a Zen V4 I thought that I would throw together a preamp circuit to drive it. I believe that I have all of the calculations correct. Any opinions or advice are appreciated.

G

[HDTVman]

Gavin

Not even close.

1. As drawn you need a PNP transistor and reverse the Emitter/collector connection and use only one stage (one transistor, LED, resistor).

2. I would connect the bias resistor to the plate/collector connection. (Lowers the wattage requirement).

The way the stage is drawn the transistors are reverse biased. With the stages stacked the way they are the bias for the transistor connected to the tube plate will keep it turned off.

I think you should go take a look at the current sources used in the Pass amplifers again.
Later
Bruce

[Joel]

Gavin,

I'm new to solid state design - what is the purpose of all the circuitry in the plate circuit of the 6SN7?
Also, where is the gain control? I didn't see one.

joel

[Brett]

G,

Learn from a <a href="http://home.pacifier.com/~gpimm/">master</a>. Especially take note of <a href="http://home.pacifier.com/~gpimm/45_all_active.gif">this one</a> as it's similar to what you're trying to do.

Gary's BBMCCS will be the load for the driver stage in my 813PP monster.

Joel,

The purpose of the CCS is to replace the normal anode loads of resistor, choke or IT primary with the highest possible impedance broadband load. It maximises the linearity of the tube (if well implemented) and usually gives the circuit a bit more gain (gain=u). It also stabilises the operating point of the tube. The loadline will be near horizontal.

[G]

Hi Brett,

If you look at the gain stage of the diagram that you posted I've done the same thing as Gary did. The only difference being that I biased the LED's separately and added the bypass caps. It's merely a fancier C4S.

G

[Joel]

Thanks for the reply Brett!

I thought the "linearity" of the tube (Transfer Characteristic) was inherent to the tube regardless of load/type of load/etc?... if not, how are they are able to draw plate curves?
Also, doesn't a fixed bias supply set, and hold, the operating point - regardless of external conditions? Hence the term "fixed"?

Sorry if I'm pestering! Just trying to figure this circuit out.

joel

[steve jones]

Originally posted by G
Hi Brett,

It's merely a fancier C4S.

G

The BBMCCS that Brett referenced (but not linked) is not a C4S variant. Take at a look at:

http://home.pacifier.com/~gpimm/Battery_biased_ccs.htm

I've been around Gary since his push-pull tube days. He originally started using a C4S as a CCS plate load on line level tube circuits. He got the itch to size it up for the SE 45 amp linked above. Later, he used a pentode as a HV ballast and isolated the SS current sensing portion of the curcuit. He's since come up with a number of versions (note: 2 connection CCSes), the battery bias mosfet constant current source (BBMCCS) being the latest.

The original C4s has around a -40dB noise figure. The BBMCCS measures better than -115dB to 1kHz. As Linda Richman would say: "It sounds like butter".

FWIW, Gary is an engineer at Tektronix and IMHO, a freaking brainiac.

Try the BBMCCS, G. It'll do you good.

Steve

[G]

Thanks very much Steve. Minus 115 dB sound very nice.

G

[G]

How does Gary keep the batteries Charged? Replacing them everytime they go dead will be a pain. Or are they used merely for potential at the gates with little if no current flow?

G

[fdegrove]

Hi Gavin,

Or are they used merely for potential at the gates with little if no current flow?

Correct,there's hardly any current drain.

Cheers,