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In Reply to: RE: 845 posted by Triode_Kingdom on July 17, 2015 at 19:26:24
It would depend on the goals. An adaptor of some sort for other testers should provide meaningful information. There is no reason why a tester capable of testing 300Bs or the like could provide useful information against published data, even curves. Comparisons to known good tubes would be even easier and very relevant.
Naz
Follow Ups:
"It would depend on the goals."
I thought the goal was to determine whether the tube is good. No?
"An adaptor of some sort for other testers should provide meaningful information."
Yes, but it won't identify all modes of failure. That means (like I already said) it's not a guarantee the tube is good. You *must* apply actual operating voltages and current to know that.
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Buy Chinese. Bury freedom.
What modes of failure would an adaptor (and of course a decent tester) not identify? The only thing we'd be doing is running the tube at lower than normal voltages. Sure a miniscule risk exists that the tube might fail at more usual HT voltage but that's not much of a risk.
Heater voltage and current requirements needs to be dealt with but even that could be supplied externally if the tester has insufficient capability.
Even the higher than normal grid bias voltage requirements would drop significantly with lower HT voltage.
Naz
"a miniscule risk exists that the tube might fail at more usual HT voltage but that's not much of a risk."
You're wrong, it's a significant risk. Lots of things can go wrong at 1KV that won't show up in a tester. Heck, it's not uncommon even for low power tubes to test good on a tester, yet fail in actual service. Anyone who repaired radios and TVs for a living in the '50s and '60s can attest to that.
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Buy Chinese. Bury freedom.
You're wrong, it's a significant risk. Lots of things can go wrong at 1KV that won't show up in a tester.
Care to quantify that statement with some fact?
Heck, it's not uncommon even for low power tubes to test good on a tester, yet fail in actual service. Anyone who repaired radios and TVs for a living in the '50s and '60s can attest to that.
So why bother testing at all? Let's just put all tubes straight into amps for testing? There are no guarantees in life, everything has a degree of risk and we live with calculated risk all of our lives.
The issue here is your position that you cannot get meaningful information about the performance of an 845 at lower voltage than 1KV and that's plain wrong! Besides not all amps are run at 1KV especially in the DIY world.
Naz
"The issue here is your position that you cannot get meaningful information about the performance of an 845 at lower voltage than 1KV"
I didn't say that.
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Buy Chinese. Bury freedom.
Ok, can I politely ask what it is you are saying so we are on the same page? What specifically can't we test for?
Of course the ultimate test is always in the product. But using a tester that does not normally provide for an 845 could be reasonably used by adopting some sort of adaptor. This tester at say half the USUAL operating voltage of the tube and at the same or if possible even higher current but within the ratings of the tube should provide an extremely high degree of confidence that he tube is good and doing what it was designed to do.
In addition, a good tester can provide other performance information such as actual curves etc (some testers at least). But let's face it, often the user is only interested in whether the tube actually works, heaters etc and that the tube has good emission.
My position (in response to the poster's question) is simply that the idea of some form of tube adaptor is very valid and useful. Some testers even provide means of testing tubes that are not fully catered for, clip leads etc.
Naz
"This tester at say half the USUAL operating voltage of the tube and at the same or if possible even higher current but within the ratings of the tube should provide an extremely high degree of confidence"
None of my testers will output 500V/100ma. I think you're changing the parameters to suit an opinion that was incorrect in its original context.
"My position (in response to the poster's question) is simply that the idea of some form of tube adaptor is very valid and useful."
But it won't guarantee that a high power tube will be operational or satisfactory in service.
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Buy Chinese. Bury freedom.
If a tester can test an output tube like a 300B or the like then it's capable of a meaningful test of an 845 with some adaptation. Whether it's 500V or even 300V, 100mA or 40mA it really doesn't matter, just refer to the curves on the data sheet.
You can test any tube at much less current than would be considered "normal". In fact I've seen many designs that run tubes at a tenth of the current with great results but before you go off, no they weren't output tubes.
I'll repeat, is it possible that the tube may fail at higher voltages and current? Possible but absolutely minimal. Your solution is to plug the tube into an amp. What if it has an H/C short, certainly a greater risk.
I keep asking you to tell me the parameters that couldn't be tested but you keep offering the same line with no substance.
Remember that I qualified my original reply with "it depends on your goals". You should have taken note before jumping all over it.
You hold your opinion and I'll hold mine.
Naz
"I keep asking you to tell me the parameters that couldn't be tested but you keep offering the same line with no substance."Everyone in the business has seen tubes that test fine but fail to work properly in live circuits. Are you willing to guarantee that every 211/845/813/811 that tests OK at 500V won't arc at 1KV? What about 6L6s or 6L6GCs? Every example that seems OK at half anode voltage will also be OK at the manufacturer's rating? If you say "yes" to this, it only means your experience is too limited to know better.
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Buy Chinese. Bury freedom.
Edits: 07/23/15
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