Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bruno on December 07, 2010, 11:44:09 am
-
Like this...
http://www.tubecad.com/may2000/
I might try this out, not sure if it'll add anything useful though.
-
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.
-
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).
-
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.
-
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
-
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