I don't think I'm getting you, sorry poor english.... I was meaning that I was sure I was measuring DC, but good hint, anyway!
Oh, that crapola. Canceling inductance in noninductive resistors.
Don't skip the grid stoppers. Carbon will work fine for that (the issues you raised are true but unimportant in that position), but metal film will also be fine. The critical thing is getting the bodies close to the grid pins, the material is pretty unimportant.
Yes. The inductance of a spiral cut resistor is irrelevant - the worst it will do is lower the frequency of any parasitic oscillation. The resistance is what does the job. A potential VHF oscillator is not too fussy about exactly what substance is used by those pesky audio fans to add resistive damping and kill it. UHF, maybe, but I doubt if a KT88 can amplify enough at UHF to become an oscillator.SY said:
Funny thing was that even if they were highly inductive, there is no way to guarantee uniformity across sectional cuts between individual resistors. I mean, while manufacturing them there's no guarantee that ink printings on the outter side correlate to inside spiral orientation in each piece.Oh, that crapola. Canceling inductance in noninductive resistors.
But! Even if you can guarantee that, it ain't a scientifical approach to what canceling inductances is, meaning that way you won't never ever cancel anything.
Sorry for the offtopic, now gentlements we can go ahead and fix that crazy couple of tubes.
It is extremely likely that all resistors from the same production line (and perhaps all resistors using the same technology) have exactly the same helix orientation. There is absolutely no reason why a maker would want a mix of right-hand and left-hand threads as that would simply raise his production costs by having two types of machine or controlling software. Given that, to get the opposite helix you would need to step through a mirror - wiring the resistor back-to-front does not achieve helix reversal.regiregi22 said:
What I was meaning is that, while asumming what I mark in bold, maybe (note the "maybe", because haven't ever been on a mfr. plant) the machine that puts the coating on the resistors randomly pick them up and paint them. But, anyway, doesn't really matter because it will not change an opposite helix, just one the other way around.
This is basically correct. But yes, the helix is not rotated through the fourth dimension.
good question, had problem with standard 0,6W carbon, they are rated max 300V
at 400-500V it became suddenly a xxMohm from 100k..even without sparks
If I'm not wrong, that grid resistor is only going to "see" 65v across it, isn't it?
Not 65VDC across it, in its quiescent state. However, it will also see whatever your maximum signal swing is, but it really isn't about voltage.
The "size" of the resistor needed in Watts will depend on the maximum grid current that is drawn through the resistor.
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The grid stopper shouldn't have any significant signal voltage across it until clipping. And even then, it will be quite limited.
With a little thought, this circuit can be re-arranged slightly to give more power and much better clipping/recovery characteristics. Perhaps that's a better use of brain-power than trying to justify parallel resistors in "opposite directions."
With a little thought, this circuit can be re-arranged slightly to give more power and much better clipping/recovery characteristics. Perhaps that's a better use of brain-power than trying to justify parallel resistors in "opposite directions."
Haven't had the time yet to test it with grid stoppers, but maybe the problem just come to be not having paralleled opposed resistorsI guess RegiRegi22's original problem has been dwarfed by the perils of grid stopper resistors?
I don't think you can make that leap with your argument.
I personally believe that paralleled grid resistors is really a lot to do about almost nothing. That is, it is almost like the search for the Holy Grail of AC cords where any possible gains are so minute as to be unmeasurable.
Meanwhile, the original problem appears to be an oscillation (that should really be confirmed with an oscilloscope if the builder has one), but everyone is now stuck on the minutia of grid resistors and the finer practices thereof.
I kind of see the original problem as the elephant in the room and that needs to be understood (i.e., root cause analysis) and fixed. Then move on to the next problem (if one exists) and fix that.
The grid resistor discussion is probably a distraction for the builder (RegiRegi22) and preventing the timely fix to the original problem (in my opinion).
I have used 10Kohm to get low distortion and good damping factor with low feedback.
This is not a common Push-pull with the KT88 and it is very different to the commercial products.
I get only 25-35w instead of 100w.
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