In my opinion, "Old School" design of tube equipment is testament to good reliable operation and longevity of the tubes.
Bleed-down resistors used across B+ capacitors are not a bad idea either.
Not knowing the particulars of the specific circuit discussed, I would tend to think that perhaps adding a high value (megohms?) bleed-down resistor after the B+ cutoff switch might be a sensible idea.
Bleed-down resistors used across B+ capacitors are not a bad idea either.
Not knowing the particulars of the specific circuit discussed, I would tend to think that perhaps adding a high value (megohms?) bleed-down resistor after the B+ cutoff switch might be a sensible idea.
Tubes can be powered up for years at high plate voltages and no heater power without damage, since no current flows. It's the short period at turn on and turn off where the damage happens.
Turn off is usually worse case since all the current tries to flow through less and less of the cathode as it unevenly cools off. As I said before I saw sparks fly inside al old 6L6 type at turnoff. The old ham radio guy that I learned from as a kid told me that this kills tubes, turn the B+ off first.
The wise old one should remember the days of fixing old AA5 radios. When the radio got sick and needed a new tube, which one was it most of the time? It was usually not the 50C5 or 50L6 audio output tube that ran at or over 100% of it's plate dissipation spec. It usually was the 35W4 or 35Z5 rectifier tube that makes the B+ for the whole radio, but dissipates less than a watt under normal duty.
The old TV picture tube rejuvenators ran the heater at about 9 to 12 volts depending on the setting, but the zap button that blasted the interface discharged a cap between the cathode and all other elements in the tube wired in parallel. The cap was a small electrolytic, but I can not remember the details now.....it was over 50 years ago.
Turn off is usually worse case since all the current tries to flow through less and less of the cathode as it unevenly cools off. As I said before I saw sparks fly inside al old 6L6 type at turnoff. The old ham radio guy that I learned from as a kid told me that this kills tubes, turn the B+ off first.
The wise old one should remember the days of fixing old AA5 radios. When the radio got sick and needed a new tube, which one was it most of the time? It was usually not the 50C5 or 50L6 audio output tube that ran at or over 100% of it's plate dissipation spec. It usually was the 35W4 or 35Z5 rectifier tube that makes the B+ for the whole radio, but dissipates less than a watt under normal duty.
The old TV picture tube rejuvenators ran the heater at about 9 to 12 volts depending on the setting, but the zap button that blasted the interface discharged a cap between the cathode and all other elements in the tube wired in parallel. The cap was a small electrolytic, but I can not remember the details now.....it was over 50 years ago.
Ya that's not a bad idea. Right now, It relies on the tubes being hot enough to conduct all the current out of the cap - the main bleed resistor being before the relay. Megohms would be too high IMHO, but 100k will do.
I just checked - there is still 110V on the tubes from using it yesterday. At least the caps aren't leaky 🙂
I just checked - there is still 110V on the tubes from using it yesterday. At least the caps aren't leaky 🙂
I would agree, but these tubes are just small receiving tubes.
Perhaps they are just hot enough from sitting on a 65 degree chassis to flow a small current which leads to some kind ion bombardement or something - I have no idea just taking a guess.
6N1P's datasheet lifespan is 500-1000 hours (depending on what datasheet you're reading).
6 months is 4000+ hours.
The tube might be dead as well even with the heaters on 😛
True, but I've used 6N1P tubes continuously for more than 2 years in other set ups 🙂 It's usually rare a signal tube wears out unless you're running it hard.
I do usually undervolt the heaters though. I find it makes for a longer lasting tube. 5.9V-6V for a 6.3V tube for instance. Still within spec of course.
I do usually undervolt the heaters though. I find it makes for a longer lasting tube. 5.9V-6V for a 6.3V tube for instance. Still within spec of course.
That's easy. Preheating a tube rectifier means that when you switch on the high-voltage from the secondary, the tube rectifier is looking into a near short (the discharged electrolytics), which surely will make it fail prematurely.
This is a fundamentally different case as for the amplifier tubes.
Jan
The getter requires heat to remove gas. A cold getter may even release some of the trapped molecules over long periods of time. Maybe the getter they used in your 6n1p is particularly prone to that. Anyway, a tiny amount of gas might just sustain a very faint glow discharge while plate voltage is on. Not visible but detrimental to the cathode coating.
It will be very interesting to see whether these tubes come back to life when they are run hot for a couple of hours ...
It will be very interesting to see whether these tubes come back to life when they are run hot for a couple of hours ...
This might be a clue to the effect. If so, i do not expect this tube to recover as
the slow gas-discharge will create ions that will hammer the cathode.
The phenomena reported is new to me, and i have not seen it in literature.
Isnt the debate about damage by HT rising at switch on, or conversely, remaining elevated at switch off (when heaters are switched at the same time), largely irrelevant?
If PSU caps have a bleeder resistor, and capacitors are ordered correctly then the HT ramps up, or down, at a slow enough, or quick enough rate, to prevent the high anode voltage without sufficient cathode heat situation being a problem?
What am I missing? For once, I agree with Wise Old Tech, it seems like over complicating, or being "clever" with switch on routines, is the culprit.
FWIW, I do actually turn off unused electrical outlets on my home, despite the UK 3 pin outlet being the safest outlet worldwide, and I abhor leaving items on 'standby' 😀
If not, then the life expectancy issue of the 6N1P/quality of manufacture seems to be the likely culprit.
What decade where these 6N1P?
I try to buy my soviet tubes from the 50s, 60s or 70s at the youngest.
All my 6N2P, 6N3P, 6N5P, 6P6S, 6P3S are all at least 70s, if not way older, before the breakup of the USSR.
I've read multiple times that post 70s reliability/quality is garbage.
Also, as a final aside, some stock from some military storage locations is likely compromised, and I would guess that would include many from UKR (Chernobyl)
I speak from experienced acquiring many Soviet neons, which were damaged by radiation - browned glass - the result being weakened, embrittled glass, prone to microfractures
It could just be bad luck.
Just my 2 pennies worth.
If PSU caps have a bleeder resistor, and capacitors are ordered correctly then the HT ramps up, or down, at a slow enough, or quick enough rate, to prevent the high anode voltage without sufficient cathode heat situation being a problem?
What am I missing? For once, I agree with Wise Old Tech, it seems like over complicating, or being "clever" with switch on routines, is the culprit.
FWIW, I do actually turn off unused electrical outlets on my home, despite the UK 3 pin outlet being the safest outlet worldwide, and I abhor leaving items on 'standby' 😀
If not, then the life expectancy issue of the 6N1P/quality of manufacture seems to be the likely culprit.
What decade where these 6N1P?
I try to buy my soviet tubes from the 50s, 60s or 70s at the youngest.
All my 6N2P, 6N3P, 6N5P, 6P6S, 6P3S are all at least 70s, if not way older, before the breakup of the USSR.
I've read multiple times that post 70s reliability/quality is garbage.
Also, as a final aside, some stock from some military storage locations is likely compromised, and I would guess that would include many from UKR (Chernobyl)
I speak from experienced acquiring many Soviet neons, which were damaged by radiation - browned glass - the result being weakened, embrittled glass, prone to microfractures
It could just be bad luck.
Just my 2 pennies worth.
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Cathode coating poisoned by ion bombardment, imperfect vacuum. Built this one in 1968 & included a switch to shut down the mag preamp 12AX7 heater since it would seldom be used. But it always works when I hook it up to a phono.
The 12AX7 is from a previous generation when quality was at its best.
That other thing is an HP71B BASIC HPIL from 1984, more powerful than a locomotive!🙂
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It's not complicated. Rather than running the phono stage all the time, I only run it when the selector is set to phono. I thought just switching the heaters would be good enough to use as a switch. It wasn't. Now B+ and heat are both switched in and out when selecting phono.
The tubes were 6N1P-EV from the 80's I think. I've replaced them with 6N1P (not EV) from 70's. 6N3P tubes I have are largely from the 90's but they work fine.
The tubes were 6N1P-EV from the 80's I think. I've replaced them with 6N1P (not EV) from 70's. 6N3P tubes I have are largely from the 90's but they work fine.
Perhaps, then just bad luck and a bad/not actually NOS tube?
I'd agree that I have some 80s and 90s tubes that work fine, but their characteristics spread over at least +/- 50% when tested at a standard operating point.
This was particularly true for the wire ended 6P30B-R, where of 20, I managed perhaps 3 that tested within 10%, and a pair where emission was so low as to be almost useless, and another pair where idle current was suspiciously high, more than 3 times the lowest measured. I admit to not measuring grid currents, but no matter what I did those suckers just ran away - so I suspect gas.
I have also bought some 6N1P from the 80s which looked perfect, except for blued pins. Deoxit or contact cleaner would not shift the tarnish, which I put down to heat - meaning that they weren't NOS but good looking equipment pulls.
I'd guess it could be either, or none, of those scenarios.
I'd agree that I have some 80s and 90s tubes that work fine, but their characteristics spread over at least +/- 50% when tested at a standard operating point.
This was particularly true for the wire ended 6P30B-R, where of 20, I managed perhaps 3 that tested within 10%, and a pair where emission was so low as to be almost useless, and another pair where idle current was suspiciously high, more than 3 times the lowest measured. I admit to not measuring grid currents, but no matter what I did those suckers just ran away - so I suspect gas.
I have also bought some 6N1P from the 80s which looked perfect, except for blued pins. Deoxit or contact cleaner would not shift the tarnish, which I put down to heat - meaning that they weren't NOS but good looking equipment pulls.
I'd guess it could be either, or none, of those scenarios.
Blued pins is a result of thin film interference coming from iron oxide and is probably a result of the production process.
Perhaps these Sovjets need some hours run-in before measurement?
Perhaps these Sovjets need some hours run-in before measurement?
Not heat then?
I'm fairly sure the pins are not iron, but tinned copper.
Where would this iron oxide come from?
(No Iron oxide (I, II, III) I know of is blue)
Would be interesting to see of rust renovater removes it...
All the 6P30BR were run for probably 50hrs, and measured at various points. They did change, but not much, the worst just ran away no matter what operating point
I'm fairly sure the pins are not iron, but tinned copper.
Where would this iron oxide come from?
(No Iron oxide (I, II, III) I know of is blue)
Would be interesting to see of rust renovater removes it...
All the 6P30BR were run for probably 50hrs, and measured at various points. They did change, but not much, the worst just ran away no matter what operating point
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Be serious 😛 , the tube pins are not from copper , but kovar , an nickel–cobalt ferrous alloy with thermal expansion similar to glass . Otherwise the thermal stress would crack the glass .
Usually if an 6n1p is used for some time you would see some blackening on the glass , as it runs pretty hot ( 600mA filament )
Usually if an 6n1p is used for some time you would see some blackening on the glass , as it runs pretty hot ( 600mA filament )
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I know it is an alloy, but not what its constituent elements are.
Nickel is not ferrous....(Ni not Fe)
Kovar is an alloy with ferrous content (which I didnt know, ty)
But be serious.... if you're going to correct me, that's cool, thanks for the education, but be correct with the terminology.
Super Alloy KOVAR (UNS K94610)
Funnily though, the 6N1P are the only soviet tubes I have with ANY oxidation on the pins, no matter the origin, or explanation. I find that a little odd.
Nickel is not ferrous....(Ni not Fe)
Kovar is an alloy with ferrous content (which I didnt know, ty)
But be serious.... if you're going to correct me, that's cool, thanks for the education, but be correct with the terminology.
Super Alloy KOVAR (UNS K94610)
Funnily though, the 6N1P are the only soviet tubes I have with ANY oxidation on the pins, no matter the origin, or explanation. I find that a little odd.
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Simple to see that they are NOT the same, by any means.
A rectifier tube starts with a shorted load: the uncharged capacitor, and if preheated when AC HV is applied, it will pass A LOT of current, way more than it will ever pass in normal operations, until it gets charged.
A Power tube, unless preheated with no bias (which is crazy) and then slammed with HV, will only pass idle current , not even maximum current in operation.
2 completely different situations.
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Ummmm, normal use wears tubes, by definitio0n.
No need for high voltage cold tube stripping or any fancy explanation for a normal issue.
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So does a cathode-biased power tube with a cathode bypass capacitor. Sure the inrush is less, but that's a matter of degree, not category.