This is for all those tube amp enthusiasts and hackers out there. I wanted to build a tube stereo amp that I could be proud of. However in the course of wiring it up I found that some 6AU6s just refused to bias where they should.
I have a 1966 copy of the RCA Receiving Tube Manual and having designed electronics of all sorts for about 30 years, I understand that the published data on a device need be taken with a wee grain of salt sometimes. But the tube data published in these books is definitely NO guarantee of behaviour in a real circuit for any one specimen.
I like the little plate curve family charts, as in the picture above, in the book and THAT is what I wanted to see for the tubes I had. Using a tube tester, even a well-calibrated, high quality one will only give you one data point on one plate curve amongst that family. And you don't even know which curve it is. It's not very illuminating. Buying a curve tracer on the market can be expensive and rare (You may find an old TEK 570 on EBAY once a year for $3000 or up) and finding one locally is out.
So I decided to build one.
P.S. I have completed some enhancements to this TCT here: