A PC + a box make a tube curve tracer

Hi,

During past semester I have been supervising a student project at the University of Technology here in Goteborg. The result: a computerised tube tester, curvetracer and matcher. Interested ? The students are now looking to find some financing to turn this prototype into a product.
Have a look at some photos and screenshots in this thread on a swedish
tube forum (unfortunately the posts are in swedish only).

http://www.gmf.se/forum/topic.asp?TOPIC_ID=80000

The thing collects measurement results in a data base and automatically finds matched pairs/quartets etc.

Any ideas on what fancy things this should be able to do ?

I think that in time it should be possible to offer this as a kit to members of this group

Alex

> some photos and screenshots in this thread on a swedish tube forum (unfortunately the posts are in swedish only).

Many of the signatures are english (or american); and I see the software is all english/swenglish.

> looking to find some financing

Unless Swedish investors throw money at you, it might be time to do a rough description in simple english. english is an awful language, but somehow it has become the most universally read language in technology and money communities.

> Any ideas on what fancy things this should be able to do?

The graph of 12AT7 seems to exceed the 12AT7's plate dissipation rating. Isn't it showing 393V on the plate and ~32mA current? That's 12.5 Watts. Curve-tracers usually do go way past the ratings; but it has to be pulsed. It might be good, especially with "precious" tubes like vintage bottles, to enter a plate dissipation rating before testing, and have the test limited to very-short pulses outside that rating, and an additional fail-safe function to kill power if Pd is 200% of rating for more than 0.1 seconds.

Also: when you test at high power, you should run the curve going up and coming back down again. You will see a difference because the grid and plate heat and expand, the cathode electron cloud is depleted.

Also: in most useful audio circuits, we don't use tubes far outside their ratings. SE Class A sits right at the Pd rating. P-P Class AB sometimes peaks outside the Pd parabola, but actually most circuits don't. Only OTL speaker amps routinely swing far above the Pd parabola. So it might be wise to have a function "never swing beyond Pd rating". It will test large current at low voltage, and low current at high voltage, but not both. (Maybe a mark to indicate "terminated for Pd limit.")

As a very unusual case: for "vari-Mu" limiters, the shape of the curves over a WIDE range of current is interesting. Class A amps don't swing 2:1 of current, Class AB rarely more than 3:1 or 4:1, but a tube limiter will often be swung down more than 10:1 to get a large change of gain. Log scale graphs would be nice to see. (It might of course be easier to export the data into eXceL or other number-plotting program.)

What is the interface? Printer-port? It should probably be USB before it escapes from the lab. Already I can buy PCs with no printer port, XP hates to let applications touch ports directly, and Macs never had IBM-type printer ports.

PRR, thanks for your valuable comments. The Pa(max) limit is one of the items on the "to do " list. We'll see if there'll be a continuation of the project at the University or if it will have to be taken off campus.
I think it could be turned into a DIY project in some form. We'll see what becomes of it.

Alex