Hi,
a few weeks ago, the issue of output valve matching was raised by NG regula r Trevor Wilson in a post relating to the Peavey Classic 60.
In a subsequent post he mentioned the AVO VCM163 - the last and possibly be st valve tester made by that famous brand.
Intrigued by the unique method employed by the AVO, I experimented with var ious circuit lash ups on my bench and after a few stages of evolution and u sing a couple of bright ideas of my own wound up with a very handy output v alve tester capable of doing bias matching and far, far more.
My prototype tester is now pictured & fully described on the ESP web site b y my good mate Rod Elliot as "Project 165".
My example was built using a small plastic box and other bits lying around the workshop and employs externally a standard 240:240 isolation transforme r, a Variac, a couple of DC bench supplies for heaters and negative grid bi as plus dual trace scope and DMM. It performs equally well using a DSO like the Rigol or a regular analogue job like my ancient BWD821 for waveform mo nitoring.
Please take note of the SAFETY WARNINGS - this is NOT a project for beginne rs or clever folk who like to take short cuts.
Questions and comments welcome ....
.... Phil