Useful article, thanks for posting.
I liked this part:
Degassing
Tubes that may have gassed up can be partially degassed by putting them in the equipment and running them for several hours with filament voltage only applied. After the initial filament only degassing; operation for an hour or so at reduced plate and screen voltages is desirable. This allows the getter to soak up and hold any residual gasses. In directly heated filamentary tubes, the getters are generally zirconium bearing materials, which depend on heat to activate the gettering action.
But apply only filament tension is impossible in most these stupid current tube amps now adays as they delivery grid and HV B+ just afew seconds after the power on, there is no switch for manually activate the HV.
As result short tube life will occour, what keep tubes manufacturers happy...
I liked this part:
Degassing
Tubes that may have gassed up can be partially degassed by putting them in the equipment and running them for several hours with filament voltage only applied. After the initial filament only degassing; operation for an hour or so at reduced plate and screen voltages is desirable. This allows the getter to soak up and hold any residual gasses. In directly heated filamentary tubes, the getters are generally zirconium bearing materials, which depend on heat to activate the gettering action.
But apply only filament tension is impossible in most these stupid current tube amps now adays as they delivery grid and HV B+ just afew seconds after the power on, there is no switch for manually activate the HV.
As result short tube life will occour, what keep tubes manufacturers happy...
Healthy valves don't suffer from having all voltages applied simultaneously. Valves which may suffer (such as high power transmitter valves) should either have automatic sequencing or qualified/trained operators. Manual sequencing by the average audiophile/musician is more likely to do harm than good.
Hard to believe it, I have see many famous amps using Pentodes which tube life is only 2 to 3K hours for 6550/kt88.
I again will mention the michael Boelle 6C33 datasheet:
Minimum warmup time is 120 seconds, regular warmup to steady state is 600 seconds, this is in military use, in hi-fi use it must be much more longer.
On page 1:
http://www.jogis-roehrenbude.de/Russian/6C33C/6C33C-B-6S33S-VExtendedDatasheetMB.pdf
I unknow other tube that mention it, every tube had a minimum warmup time, cold start is not recomended if you wish long tube life.
Of course tube manufacturer and vendors will disagree.
That datasheet does not say, as you appear to think, that the valve has to be warmed up for 120s/600s before it is safe to use it. It actually says that it needs to warm up for these times before it reaches 90%/full emission.
The stated lifetime (>750hours) is conditional on satisfying the plate current and voltage conditions, not the warm-up conditions. For longer life (2000-3000 hours) it specifies low envelope temperature and low vibration, not long warm-up.
For normal power valves operating within their specifications 2000-3000 hours can be regarded as expected operation time. If you need longer life then you either have to significantly derate them or use special quality versions. Even SQ versions rarely guarantee more than 10k hours.
The stated lifetime (>750hours) is conditional on satisfying the plate current and voltage conditions, not the warm-up conditions. For longer life (2000-3000 hours) it specifies low envelope temperature and low vibration, not long warm-up.
For normal power valves operating within their specifications 2000-3000 hours can be regarded as expected operation time. If you need longer life then you either have to significantly derate them or use special quality versions. Even SQ versions rarely guarantee more than 10k hours.
That datasheet does not say, as you appear to think, that the valve has to be warmed up for 120s/600s before it is safe to use it. It actually says that it needs to warm up for these times before it reaches 90%/full emission.
It need warmup in a military use, in hi-fi use the times must be longer, but some 6C33 amps use 10 seconds delay only for this tube.
It is easy to figure warmup is very important in a tube, this times are for military use with service warranty of 1000 hours.
Any help for a tube life is welcome, slow and long warmup is not neglegibe.
A cold start is so stressing some tubes even produce noises when it receive the HV in a cold start.
Joule Electra claim his amps sports 5 to 10K hours for the 6C33, but it use a slow manually start with a Variac.
I mean say 3000 is short life for a Pentode.
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Old thread but helpful and figured I'd share my results. I recently acquired a couple dozen nos 2A3 RCA tubes. Unfortunately they spent the last 30 years in a outdoor storage shed in less than perfect conditions. After cleaning corrosion from the pins I started testing the tubes. Hickok tester showed that all but 1 of the later date grey plate tubes were good. Sadly test results showed that 7 out of 8 early tubes with black plates and spring tops were bad. All bad tubes had weak to no glow from the heaters. I baked all bad tubes in the oven @265 degrees for 3 hours then turned off the oven and let them cool slowly before taking them out. I then rechecked the 7 black plate tubes I had baked in the oven and 4 of them tested perfect, the 1 oven baked grey plate tube still checked bad. I was still a bit skeptical so I plugged a pair of baked tubes in the amp and listening test proved they worked great.
I can't say why baking the tubes in the oven helped, all I know is it was 50% successful at saving some nos tubes from being thrown in the trash.
Side note -none of the tubes I baked had any signs of heat damage to the bases.
I can't say why baking the tubes in the oven helped, all I know is it was 50% successful at saving some nos tubes from being thrown in the trash.
Side note -none of the tubes I baked had any signs of heat damage to the bases.
It is plausible that heating the getter material on the glass may assist in reducing the stray molecule concentration (that may have accumulated slowly over decades from out-gassing or very light leakage), and may do that better if the glass temp is raised somewhat higher than for normal operation, but that is a balance due to increased outgassing from the glass (more glass is hotter than during normal operation) - the plate and other internals are not raised to the same temperature as during operation, so increased outgassing should not be an issue from those parts. It is also plausible that getter material that has got to the end of its service life may 'have a little more performance in it' if raised to a temp a bit more than in normal operation.
None of that goes directly to the lack of emission issue. Perhaps more testing of those valves before baking would have help awareness - eg. was the filament resistance the same before/after.
PS. re-read the thread, especially comments from Merlin.
None of that goes directly to the lack of emission issue. Perhaps more testing of those valves before baking would have help awareness - eg. was the filament resistance the same before/after.
PS. re-read the thread, especially comments from Merlin.
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I had some weak/gassy WE 429a pentodes and baking them didn't make any difference. Went as far as using my coffee roaster pid controller to keep the toaster oven temperature stable. Those tubes had a 20v heater and one had really low emissions until you cranked the voltage up to 24. Tested normal at that point.
Ahh well, bprewit may be a scientist 
265C is probably about right for an 20-35W dissipation output stage valve. 265F is probably right for a preamp noval type valve. That's based on those temps being ball-park max temp in hottest glass region, which is significantly hotter than glass with getter on it.
265C is probably about right for an 20-35W dissipation output stage valve. 265F is probably right for a preamp noval type valve. That's based on those temps being ball-park max temp in hottest glass region, which is significantly hotter than glass with getter on it.
The highest temperature in most commercial ovens in the US is only available when you activate the oven self-cleaning feature. It locks the door during the heating time through the cool down time.
Try that on your octal tubes, and see if it melts the bakelite or other material.
Or, drive over to Bakersfield, California, and put your glass enveloped tubes out in the sun for 1 week. I hear that the UV radiation really helps those tubes.
LOL.
Oh, in 1960, the US Government declared that the US was going to go Metric.
I am still waiting.
Oh, I have parts in inches and metric, so I have both sets of wrenches.
. . . Still converting in the US.
"There will be no changes, until further notice"
Try that on your octal tubes, and see if it melts the bakelite or other material.
Or, drive over to Bakersfield, California, and put your glass enveloped tubes out in the sun for 1 week. I hear that the UV radiation really helps those tubes.
LOL.
Oh, in 1960, the US Government declared that the US was going to go Metric.
I am still waiting.
Oh, I have parts in inches and metric, so I have both sets of wrenches.
. . . Still converting in the US.
"There will be no changes, until further notice"
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My regular domestic GE goes to 550f. At least once a week to bake me some home made pizza.
Cutting the latch off the lock and putting it in clean mode is another trick of home pizza chefs, and maybe tube bakers as well. Then you can get to about 900f.
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