hagtech wrote:

Note the '63 has much higher gain.  The horizontal spacing is basically "mu".  Interestingly, the 6e6p has lower gain than both of these.  To me, the curves are beautiful.  Spacing is relatively constant, indicating superb linearity.  The tube can also push huge amounts of current.  That is not shown here, as I zoomed in to a 5mA/div scaling.  Previous posts were at 12.5mA/div.  The high slope of the curves means very low output impedance.

Fascinating! The used up tube has lower gain but we do not relay have clew as we do not have the trace of the same tube when it was new. Since it is Russian tube then even the new tubes might up to 30% difference in gain. Anyhow, I agree that the curves look examplenary, although I have no idea how this “perfect” picture would affect sound. Another interesting observation, and I do not know if I am correct in it, is that the new tube and the used tube have practically no difference in a tracer (the same is for 6C33C) beside their gain. So, are we looking back to measure just cathode emissions?

hagtech wrote:

Each tube here appears to be very good.  I see no anomalies.  There will be sonic differences, as a circuit biased for one of these will be sub-optimal for the other two.  This is a pretty large sample-sample difference.

Yes, what would be necessary is to measure a couple dozens of them and to learn where is common denominator among the 5E5P…

hagtech wrote:

Ok, next is my attempt at a 6c33.  Clearly there is not enough grid voltage to sweep this tube.  Again, 50V/div horizontal, but 25mA/div vertical.  The sweep cuts off at 200V plate because there is not enough grid volts.  Lines are at 10V/div.  Starting at 0V.

Actually 200V is enough…

hagtech wrote:

So I zoom in.  This is at 20V/div plate.  So it still gets up to 200V.  Note the distortion characteristics.  One, the curves gradually get closer together with more negative grid voltage.  Two, the slope changes.  The spacing indicates a nonlinear gain when used in circuit.  The slope means output impedance is changing.  Both will affect performance in an amplifier.  Oh yeah, I wired the tube up to do only one half at a time.  This is the 1,2 heater.

Yes, it is know that 6C33C is not as linear at trace as some other tubes. Once again I do not know how it manifest itself sonically.

hagtech wrote:

The older tube has less gain.  But something really funny showed up.  And I am not used to seeing this.  On the 76 side, notice the loop in the curve!  This must be some hysteresis.  The curves are generated by ramping plate voltage up, and then back down.  Generally, the two curves fall on top of each other.  In this case, something split them.  I can sweep slower and faster.  And the loop (I forget already) I think is larger at slow tracing (which is supposed to be more accurate as it gives the grid step more time to settle).  My guess is that the loop might be caused by grid current.  I dunno.  However, we may have stumbled upon some practical indicator.

Jim, it might absolutely everything with 6C33C. It is very low standard tube with huge run off of it’s parameters. I would need a couple days to absurd what I see and to interpret how the seen might affect the way in wish the tubes are being used in my amp.

Well, it is not necessary a fully qualified urban legend as the problem does take please with fixed based 6C33C but..... only under certain conditions. I have written about it a lot on my site but will very briefly recall it again.

Dima might be correct pointing the reasons for anode overhearing but there is one interesting aspect in it. It is irrelevant if the tube is used up and old one or a brand new right from a box. The 6C33C “go red” ONLY if it is insufficiently heated before it begin to care high grid currant. Trust me guys; I burned a lot of 6C33C. Sine 1996 I used BAT VK60, then ML2, then Melquiades… all of them around the 6C33C (Although BAT used automated bias – it is a different story). I always was very liberal with them – $6 per tube you can do any stupid things for them. So the conclusion that I made is that if do not dissipate on full 6C33C more then 50-55W and let it to burn for 45 minutes before loading the tube with a strong string then the 6C33C does not have any temperate instability and any secondary emission. Sure, with low sensitively speakers when people pump a lot of current across the grid and running the tube “cold” (15-20 minutes of heard make the tube still “cold”) do create the avalanche heating effect. Interestingly is that if the tube was “avalanched one than it will have tendency to do it in future….

Jim, it would be very interesting if you do the following test. Take a half of the 6C33C that you did not overhear yet (currant goes up and the plate becomes visibly red). Heat it for a few minutes (most like as you did) and confirm the "hysteresis". Then reset the plate current and kept running the tubes it for another 60 minutes. I presume that the temperature-inspired "hysteresis" will not manifest itself then. If it is will should up then it will be at WAY higher grid currant (close to full power) and at MUSH lower frequency.  In Melquiades, during the testing I forgot to turn my generator off and a well heated 6C33C (60 minutes) did care for half hour 10H at full power with 55W on plate. Actually it could care longer but it burned the 12R loading Miles 12W resistor….

Rgs, Romy

BTW, Jim, when will we see your version of amp with 6E5P driver? :-)

I really do not understand what conclusion you make by shutting the tube down.

OK, let me to recall. We learned that the “hysteresis” (for a lack of better world) manifest itself on used tube only. Also, what I see in the images the one of the half of the used tube has more “hysteresis” then other. I think it leads to the following considerations:

1) Your tester might have some kind of anomalies when it drive used tubes (highly unlikely)
2) This given used tube has the “hysteresis” anomaly because it was overheated by me during its service.
3) This given used tube has the “hysteresis” anomaly because it’s a Russian tune and everything imaginable might happen with it.
4) All used 6C33C has the “hysteresis” anomaly because it is a common behavior of exhausted 6C33C

Among all those cases the last one of the most valuable as it might present an objective testing opportunity about health of 6C33C. I think to confirm it would be necessary to run a few other used up 6C33C and to see of the “hysteresis” will be there. If you do not mind I would propose to send you a few other used 6C33C to see what happen. Interesting, Jim, can you elaborate more about how you think the “hysteresisation” of 6C33C might manifest itself sonically.

BTW, I use the shutting down method sometimes in my tube tester. While I measure cathode emission I drop filament voltage from 6.3v to 4V and I have observed that “fresher” tube has less emission degradation.

... output two independent traces ... at the same time?

Actually I am not preoccupied with the discovery of how the anomaly might sound. My primary interest is to discover if this “mystesises” is avoidable sign of the tube ageing. If so then it would be very good.  I will send you more used tubes…..

Also, if the tracer could do two tubes at once then it make sense to have one selected reference tube and test all candidates against its reference traces, am I right? An alternative would be to have a contemporary digital scope with ability to run one channels from memory and another from input….

do two tubes at once then it make sense to have one selected reference tube

Is this one of those shining moments?