Hi,

a few weeks ago, the issue of output valve matching was raised by NG regular Trevor Wilson in a post relating to the Peavey Classic 60.

In a subsequent post he mentioned the AVO VCM163 - the last and possibly best valve tester made by that famous brand.

Intrigued by the unique method employed by the AVO, I experimented with various circuit lash ups on my bench and after a few stages of evolution and using a couple of bright ideas of my own wound up with a very handy output valve tester capable of doing bias matching and far, far more.

My prototype tester is now pictured & fully described on the ESP web site by my good mate Rod Elliot as "Project 165".

http://sound.westhost.com/project165.htm

My example was built using a small plastic box and other bits lying around the workshop and employs externally a standard 240:240 isolation transformer, a Variac, a couple of DC bench supplies for heaters and negative grid bias 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 monitoring.

Please take note of the SAFETY WARNINGS - this is NOT a project for beginners or clever folk who like to take short cuts.

Questions and comments welcome ....


..... Phil