Well, in the world of caps you obviously are.
Thanks. Will try with the dessicants.
Best.
op.
Let us assume for the moment that you manage to dry out these caps. How long will they stay dry?
^That's what I thought when I read the earlier suggestion to try Silica gel to remove moisture. But it's the best idea, for a mini experiment. Longevity is another thing.
However, the OP wants to use these things so much, I didn't see the point in saying what you pointed out.
However, the OP wants to use these things so much, I didn't see the point in saying what you pointed out.
Throw a fish? What am I/we, a fish-truck?
Given "15Meg" from a 100V-200V plate to a "zero" V grid, and 470k grid-"leak", this is a simple DC analysis or Voltage Divider problem.
But here's a fish-nugget: another 5V on the grid of 6V6 is unlikely to blow it up quick. (EL84 could be more exciting.)
me> Given "15Meg" from a 100V-200V plate to a "zero" V grid, and 470k grid-"leak", this is a simple DC analysis or Voltage Divider problem.
Counting on thumbs (ignoring rounding error):
Say stage 1 plate at 150V, 15Meg leak in C, <1Meg grid resistor. 15Meg:0.470Meg is a 30:1 divider. So before we put tube 2 in, we expect 150V/30 or 5V at 2nd tube grid.
And 150V in 15 Meg is 10uA.
If V2 is a 12AX7, its normal bias is 1V-2V. We normally get this with a "grounded" grid and cathode standing on a 1.5k resistor. "Grounding" the grid is easy because normal grid current is under 0.5uA. In 500K this makes 0.25V, which is not zero, but is much-less than the normal 1V-2V bias, so is tolerable.
Add 10uA from the leaky cap and this node rises to 5V or so.
*IF* 12AX7 could flow large cathode current, we might expect 6V across the 1.5k cathode resistor, or 4mA. A glance at 12AX7 curves shows this can't happen unless we extrapolate above the zero-grid line.
If we do that, the super-low grid current goes way up. The >100Meg grid impedance falls to like 2k. This loads-down stage 1 and gain goes away (approximately literally: stage 1 gain becomes near unity, because Rg2 is similar to Rk1.)
With a reasonable plate resistor on V2 the poor 12AX7 won't burn-up. This will not be true for big tubes with negligible DC load. EL84 can be happy with B+=250V, Ip=50mA, which calls for Vg-k about 7V. Assume fixed-bias (which is stupid here). Adding 5V of cap-leakage to the -7V bias makes 2V bias. Plate current goes from 50mA to about 120mA. Plate dissipation (heat) rises from 12.5 Watts to 31 Watts! EL84 is rated 12W Pdiss, we sometimes find them surviving 16W for hundreds of hours, but 31W is way past that. (It also strains the power supply designed for 60mA-70mA total load.)
In cathode-bias the tube and Rk split the difference, and current may rise "only" to 85mA, 21W Pdiss.
However smoke is often a great teacher. And blowing up a few EL84 is not a global disaster. Blowing up the tube *and* the transformers could be a personal budget dent, but hey, old caps must have "tone"!
As for drying them out: the heat of a chassis "will" do that. While you may burn other parts (and maybe the caps) in the first hundred hours, after that the caps will be dry inside (if they haven't broken-down completely).
Counting on thumbs (ignoring rounding error):
Say stage 1 plate at 150V, 15Meg leak in C, <1Meg grid resistor. 15Meg:0.470Meg is a 30:1 divider. So before we put tube 2 in, we expect 150V/30 or 5V at 2nd tube grid.
And 150V in 15 Meg is 10uA.
If V2 is a 12AX7, its normal bias is 1V-2V. We normally get this with a "grounded" grid and cathode standing on a 1.5k resistor. "Grounding" the grid is easy because normal grid current is under 0.5uA. In 500K this makes 0.25V, which is not zero, but is much-less than the normal 1V-2V bias, so is tolerable.
Add 10uA from the leaky cap and this node rises to 5V or so.
*IF* 12AX7 could flow large cathode current, we might expect 6V across the 1.5k cathode resistor, or 4mA. A glance at 12AX7 curves shows this can't happen unless we extrapolate above the zero-grid line.
If we do that, the super-low grid current goes way up. The >100Meg grid impedance falls to like 2k. This loads-down stage 1 and gain goes away (approximately literally: stage 1 gain becomes near unity, because Rg2 is similar to Rk1.)
With a reasonable plate resistor on V2 the poor 12AX7 won't burn-up. This will not be true for big tubes with negligible DC load. EL84 can be happy with B+=250V, Ip=50mA, which calls for Vg-k about 7V. Assume fixed-bias (which is stupid here). Adding 5V of cap-leakage to the -7V bias makes 2V bias. Plate current goes from 50mA to about 120mA. Plate dissipation (heat) rises from 12.5 Watts to 31 Watts! EL84 is rated 12W Pdiss, we sometimes find them surviving 16W for hundreds of hours, but 31W is way past that. (It also strains the power supply designed for 60mA-70mA total load.)
In cathode-bias the tube and Rk split the difference, and current may rise "only" to 85mA, 21W Pdiss.
However smoke is often a great teacher. And blowing up a few EL84 is not a global disaster. Blowing up the tube *and* the transformers could be a personal budget dent, but hey, old caps must have "tone"!
As for drying them out: the heat of a chassis "will" do that. While you may burn other parts (and maybe the caps) in the first hundred hours, after that the caps will be dry inside (if they haven't broken-down completely).
Great, PRR. But also consider the screen grid of such a EL84, with much less dissipation capability. I believe that G2 will be destroyed sooner than plate, melting their wires and making an entire shorted tube.
Personally, I don't play Russian Roulette with electronics.
Back in tech school, my instructors made that abundently clear, and strict warnings.
So, I don't know a good reason why anybody would want to play around with "iffy crap" in the first place.
And over the decades, I'm sure all of the thousands of my customers would feel the same way.
They came ot me for professional servicing, trusting my experience, and along with that I certainly didn't need to get sued from a liability case because of putzing around with crap parts.
It's only common sense/logic.
Back in tech school, my instructors made that abundently clear, and strict warnings.
So, I don't know a good reason why anybody would want to play around with "iffy crap" in the first place.
And over the decades, I'm sure all of the thousands of my customers would feel the same way.
They came ot me for professional servicing, trusting my experience, and along with that I certainly didn't need to get sued from a liability case because of putzing around with crap parts.
It's only common sense/logic.
G everyone. Thanks for all the feedback. And sorry for being stubborn, but I have learned quite a bit. Still won't change the fact I'm a tone freak.
LoL, I never expected I was gonna kick so many tires when I first started this thread 😀 😱
Special thanks to you, PRR.
Best.
oprtr
LoL, I never expected I was gonna kick so many tires when I first started this thread 😀 😱
Special thanks to you, PRR.
Best.
oprtr