EL84 Tube Shoot Out/ Rocket

[RJ Guitars]

I have been wondering about tube testers and curious if a modern approach could be taken to evaluate them. I know I could build myself an amp circuit with four EL-84 output tubes and use a separate 1 ohm bias resistor for each tube, then get the individual bias voltages for each tube. That would give me some useful information toward characterizing each tube and allow me to match them up accordingly.

That seems a bit too simple minded and yet wasteful of a good power amp circuit. What else does it take to evaluate a tube for the purposes of bias matching them... or as the case may be intentionally mismatching them as some have proposed for it's superior sonic contributions?

Thanks,

rj

[Rick]

The Jackson 648 is a dynamic emission tester, quite flexible and fast but far from sufficient for any half decent testing.

I take thats a no, it can't be used for any meaningful kind of matching?

Aside, I have noticed that on some amps, notably 18 watt TMB marshall based amps I think it was, unmatched or at least some pairs of EL84s would create noticeably more hum. Other pairs, presumably better matched, would hum less or comparatively little. I'm guessing that has something to do with common mode hum rejection of push pull circuits and that unbalanced pairs were only minimally rejecting hum?

[Structo]

I have noticed that too, with 6L6 tubes.
If one is biased hotter than the other (Pair) then the hum goes up quite a bit.
One of the reasons I like to have a bias control for each tube.

[FYL]

I have been wondering about tube testers and curious if a modern approach could be taken to evaluate them.

A computer-controlled tube tester/tracer is IMO the best option.

You can build one using available modules, for instance from ADTV2 in France:

Standard, full featured:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0551744281
Compact, basic:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0526580974

These should be used after prequalification for shorts, leaks and gas.

Or you can pay big bux for an Hagerman Vacutrace or mo big bux for an Amplitrex AT1000.

http://www.haglabs.com/vacutrace.html
http://www.amplitrex.com/

What else does it take to evaluate a tube for the purposes of bias matching them... or as the case may be intentionally mismatching them as some have proposed for it's superior sonic contributions?

Measuring current is quite easy. You just need two variable power supplies, one for plate and screen (derived from plate thru a resistor or an active VRM) with say 0 - 500 V, 0 - 250 mA; the other one negative for bias, 0 - 100 V 5 mA. Plus heaters supply of course. Add 1R cathode resistors and the rest of the glue and you're nearly done.

Even simpler: http://priceamp.home.comcast.net/~price ... atcher.htm

[FYL]

I take thats a no, it can't be used for any meaningful kind of matching?

It can be used for prequalification and simple tests but not for matching. I usually keep an Eico 667 for these simple tests, as it's one of the best testers when it comes to measure shorts and leaks and is real fast to reconfigure. The Jackson is very similar.

I'm guessing that has something to do with common mode hum rejection of push pull circuits and that unbalanced pairs were only minimally rejecting hum?

You're correct: the tubes should draw the same or nearly the same current, if not there could be some residual hum and various sound artifacts created by OT core current asymmetries.

Some imbalance can be a Good Thing™ as it leads to more complex tones; too much is a problem.

[RJ Guitars]

FYL,

A kind thank you sir. The tubematcher circuit was exactly what I was thinking of in my own mind but had not really sorted any of it out yet.

I also aprreciate the insight on on balance, bias, and hum.

So as a most crude method of matching tubes, is it reasonable to think that a person could use the amount of hum that a set of tubes produce (in an otherwise quiet amp) as a first cut in matching tubes?

rj

[selloutrr]

AMPLITREX

by far the best tube character curve tester on the market. For basic matching of pairs and quads the maximatcher is nice. Both operate at real operating voltages so your test results are reliable for use in most amplifiers.

The amplitrex also makes it possible to add change or create your own tests. Print test specs, test results, up to a 10 curve trace in color, and labels. As well as test for noise and microphonics. You can also save and recall data later, search the data base for matching sets, and or individual measurements.

I like to warm each tube up for 300 seconds so it has time to stablize before I run tests.

In stand alone mode it runs an automatic test warming the tube for 60 seconds before running threw a basic tube physical and displaying the spec and measurement as well as a percentage of life.

[FYL]

So as a most crude method of matching tubes, is it reasonable to think that a person could use the amount of hum that a set of tubes produce (in an otherwise quiet amp) as a first cut in matching tubes?

Yes.

[selloutrr]

I can test tubes $3 each includes hard copies of test spec, test results, and curve trace. Labels and tube life test or maximatcher matching for an extra $1 per tube to cover time and supplies.

Pm if interested.

[MCK]

I just got in a quad of new EL84M in today thinking they might be like the Russian 6P14P military which have been quite good actually.

The Sovtek EL84M *is* a rebranded 6П14П-EB = 6P14P-EV - same Reflektor factory, same tooling, same templates, same construction, same materials, same everything. Ditto for their EL84 = 6П14П = 6P14P.

Some NS-sourced batches can be quite poor because of sloppy production and lack of real QC. Vintage OTK models - I would say pre-1983 or so - are much better in that respect, they can still be found from Eastern European (r)etailers.

Russian suffixes:

P (Cyrillic) = R (Roman) = special quality
E = E = extended lifetime
B = V = ruggedized
K = K = vibration resistant

Russian equivalents of the EL84:

6П14П; bog standard version, large thick glass = EL84, 6BQ5
6П14П-EB; hardened version, longer lifetime = EL84M, 7189
6П14П-EP; special quality, longer lifetime = E84L, 7320 (quite rare)
6П14П-K; hardened version, vibration resistant = EL84F (very rare)

Excellent information in this post as well as the whole thread. For reference, the Z-Wreck is supplied with 4 Saratovs marked 6П14П;