Has anyone here tried using a SRPP 12ax7 wiring for the first gain stage?

[bruno]

Like this...

http://www.tubecad.com/may2000/

I might try this out, not sure if it'll add anything useful though.

[jojokeo]

At first I thought it was the cascode gain stage of the Firefly. But then saw it's more of a cathode follower w/ high gain and low output Z. Seems like it might work similar to a regular CF stage but maybe w/ more gain? I also kind of like the idea of a CF using a pentode/triode tube if more gain is the objective but haven't tried that one yet.

[HotBluePlates]

I was excited by the thought of trying unusal circuits a number of years ago. And it's still worth trying them out to get some practical experience with them.

What stopped me from pursuing cascode, SRPP, etc, was a simple realization:
Cascode yields roughly the same amount of gain as a pentode, from a pair of triode stages. Rather than use the cascode, I could simply use a pentode. And, either path still provides less gain than 2 triode stages cascaded.

So what I realized was that there are some very particular advantages to the unusual circuits. Often, you will find that those particular advantages are gained at a significant penalty in some other characteristic; the folks who use the unusual circuits generally have something important enough to them to accomplish that they will accept serious handicaps in other areas. For a simple example, research output transformerless amps (OTL amps).

[bruno]

I think I understand what you are saying... I haven't read through all the handicaps of this particular solution. But I believe I don't have any real use for it, it just seemed interesting.

[Fresh_Start]

Bruno - thanks for throwing that one out.  I too thought it was a cascode at first but read and learned.  Every little bit helps!

Cheers,

Chip

[Merlin]

The SRPP is a tiny push-pull power amp, and is almost pointless as a gain stage. It's output impedance is not low and its gain is not high (tending to mu/2 if the load impedance is high).

Furthermore, it's characteristics change wildly depending on the load impedance, and this generally makes for a nasty overdrive sound. 

However! There is hope... if you move the output to the anode of the lower triode then you get a half-mu stage, which doesn't exhibit the awkward overdrive characteristics of the SRPP! See for more: http://valvewizard2.webs.com/SRPP_Blencowe.pdf