Most accurate way of matching triodes ?

[Fanuc]

Hello,

I was wondering if anyone could give me some guidance on how best to match triodes both small and power types.

Is a good curve tracer required ?

Would people here (perfectionists shall we say🙂 ) rely on suppliers matching valves for you. Solid state is different I guess.

Any articles on this would be appreciated. I guess matching HV triodes like 845/211's etc would be particularly difficult because of the voltages involved.

Best Regards

 

[danFrank]

Basically the best way to match tubes is by transconductance AND by bias points.
This is rather tedious to do without a curve tracer but it can be done with 3 power supplies and a couple of multi-meters. Basically you want to use these to get the negative grid voltage points at every 5ma increment of plate current per tube. Then you match up the tubes that are closest ALL along the curve that is made with the data points that you get. Pretty easy to match tubes if you have large amounts of a tube type (20-26+ at least).
Suppliers typically will match for transconductance OR a certain bias point, but not both. Groove Tubes is the only supplier that I know of that matches BOTH bias points and transconductance. They have a computer that does this. They charge a major premium for this.
Curve tracers do what I have described, but I do not know of any that will handle the voltages of the large transmitting types like the 845/211. Luckily though, NOS types of these tubes are quite closely matched per manufacturer because of their manufacturing tolerances. I don't know about the Chinese versions and how tight the tolerances are on them.
Daniel

 

[Fanuc]

Hello Daniel,

Thanks for your reply and also my previous question about the 5687 driving 4 813's etc. I have decided to go for a GM70 triodes and am reading a lot about parafeed connections (principally _only_ because it avoids the air gap in the transformer - high permativity is then lost).

I have a suspicion Kondo audionote (japan) in there top end valve amps do not use this for some reason. Could be lack of bass. (the dcr of the plate choke perhaps ?) Or there core matieral allows high permativity with an airgap. Anyway that's what DIY is all about - experimenting.

I am going to have a look at some tektronic curve tracers and see if I can get some fairly high voltage ones secondhand that is!.

If not I may be back picking your brains 🙂

All the best.

 

[Miniwatt]

types like the 845/211. Luckily though, NOS types of these tubes are quite closely matched per manufacturer because of their manufacturing tolerances

That's what I heard from a guy who sold me two GE 211's, he'd been testing quite a lot of them, and he said they were more or less all the same🙂

 

[Dave Cigna]

If you want to match tubes to go in a particular amp, then you might as well use the amp itself to perform the measurments. You don't have to build anything! First match up sets with the same idle current, then sort them according to gain in-circuit.

What the hell...