Billfort:
Living in Canada, as you do, should hopefully provide you the ability to find a Stark 9-66 in good condition at a reasonable price
. Since I already own a Stark I am curious where you found info on the Stark you mentioned. I'm always looking for more info that I don't have already - unless it is from the boatanchor web site I previously mentioned in this thread. FYI: the Stark info at the boatanchor site is dated 1958 and does not cover tubes after 1958 so many popular tubes have no data (like 7591, 7868, etc.). Also, since the Stark is a Hickok design it may share some quirks the Hickok testers found in the US have. Namely, various anomalies in the circuitry requiring the use of ferrite beads attached to the wiring to correct so test readings are accurate and consistent. My understanding is that where to attach these beads and how many beads to attach in any one area is as much of an art as a science. I have not had any problems with my Stark, but I'm not a repair tech using my tester frequently which would reveal any anomalies.
As to this AK project, I would like to point out that the Tone Lounge site Billfort provided a link to is probably the best place online to read info on tube testers, other vintage repair gear, guitar amp repairs (which has a lot of relevance to audio since push/pull guitar amps are similar in construction/repair), etc.
Tube matching is a more invloved process than many realize. Although mutual or transconductance testers can be used to roughly measure a tube for matching purposes, the vast majority of these testers do not drive a tube to anything close to operating voltages. Most mutual conductance testers test at 150 volts or less (less is more comon, like 100 volts) - far below the typical operating volts of 250-400. Also, measuring/matching microhmos on a mutual conductance tester will not result in a matched tube or tubes as the case may be. Plate current measurement is the only way to truely match tubes and that requires uncommon equipment like a Tektronix Curve tracer, or a George Kay small tube tester (modern design that can be bought new for $$$$ - at least the last time I looked they were still made), etc. Plate current relates to the gain of the tube and matched gain is the key for tube matching. Even if a tube or tubes have equal readings in microhmos shown by a mutual conductance tester, the gain must be equal (or nearly so) for the tube or tubes to be truely matched. And, a tube or tubes with matched gain (or nearly so) are matched for audio purposes even if the micorohmos readings are not matched.
As I wrote before in this thread, a tube that tests good may not work in the actual circuit - a false positive. This is due to the limitations of most tube testers.
Undestand this, I'm not trying to throw cold water on this project or the AK'ers doing the work, spending the $$$, or donating stuff. I'm only trying to shed a little light on what's going on so that expectations do not run away from reality resulting in some disappointed members. Most tube lovers will be satisfied with the results from a mutual conductance tester for matching tubes, but others . . .
And, a tube may test perfectly, works great in many circuits, but then will not work in another circuit.
A properly operating and calibrated tester can help a lot - along with a bit of experience and keeping records of test procedures and results. I cannot stress enough keeping a record for both results and test procedures (like: warm-up time before beginning to test a tube because a cold tube may/will test differently compared to a tube that is at operating temperature, or the Life test where I count seconds to make sure I am testing tubes under equal conditions, etc., etc.) - consistency helps a lot.
'Nuff said, I'm gettin' off my soapbox, and I'm sure a few are saying about damn time
Good Luck :thmbsp:
