DC heater schematic

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Hembrook,
It looks to me like your interest on the subject is more academic than practical. If it's a scientific proof that you're after (since there's none you can find), why not embark on a set of experiments to test your hypothesis? Get some cheap Russian tubes to run on DC and AC and wait around to see which one dies first. My guess is that many of us would have long passed away before that happens.

I think one of the reasons why there's a lot of voodoo on the subject is that such a test to comprehensively say one way or the other would be difficult to conduct, let alone, design, given the complexity of variables such as brand types, manufacturing practices, designs, material used, the length of experiments, the quantity of tubes tested, etc. It would be any statistician's nightmare. This is probably why we tend to draw conclusion from non-scientifc (by that I mean non-controlled and not statistically significant) observations made by many hobbyists.

I guess the point that I am trying to make is, it really doesn't matter whether tubes run on DC or AC. Being a hobbyist, I just do whatever is convenient and sounds good. I really don't mind changing tubes when they go bad, whatever the reason. It's a part of the hobby. Sorry, I am not being very scientific here, but neither is the amount of money I pump into the hobby so far. -Min

[77seriesIII]

Eric,

That is an interesting bit of history and possible explanation on why DC on certain tubes or across all tubes started. I worked in Army aviation as both pilot and maintenance test pilot (MTP). MTP sounds sexy but we were just the stupid bastards who flew the broken aircraft out of where ever it broke or the first person to fly the supposedly fixed aircraft on its maiden flight. I can tell you volumes of information about how to actually fix the aircraft that is not in any manual and is easily classified as "folklore" by those not in the know. Also, having dealt with Military test programs where so much is tested/gone through/tested again/validated and then subsequently lost with only those being privy to the testing or had the knowledge dump transferred verbally actually know what works/doesnt work. Documentation, that is for stupid peopel who cant remember stuff is still commonly understood as a given. I had notebooks, small dark green ones, full of people's contact info, problems and fixes, HUGE database of knowledge. What did I do with it when I left service? Threw it out because no one wanted it.

Fully believe the history, background and everything about it. Do I wish it were formally documented, HELL YES, will it be documented outside of your telling it here? NOPE. To be honest this is probably the most definitive reason I have seen to date on the AC v DC debate. Prior to this as shown by Hembrook, no one can show a piece of paper saying DC is bad for these tubes. What one can find is AC is good on this tube but DC is not shown. this leaves the debate open because if DC is not shown it is bad (argument 1) or is it DC is not shown because it was not tested? (argument 2). Dunno. I do know this, I am using two 7193's (specs out as 2c22 as well) as a pre driver for a single 300B and the RCA sheet on this tube from late 40's or early 50's (dont fire me on date time if wrong...:-) )DOES state on the specs for the heater that the tube can use AC or DC. I used Frank's tube data to get this.

Good stuff thanks for all of the information.

the other erick

[hembrook]

Hembrook,
It looks to me like your interest on the subject is more academic than practical.

Min:

I think I would disagree there. It is not purely theoretical, its just that my life experience has been in a lot of worlds were voodoo is taken for granted, and tales pass around. That is why some folks spend $1000 on a power cable for their amp, and others will clip magnets to their fuel line to "save gas". Someone told them it was better, and they believed.

I think one of the reasons why there's a lot of voodoo on the subject is that such a test to comprehensively say one way or the other would be difficult to conduct, let alone, design, given the complexity of variables such as brand types, manufacturing practices, designs, material used, the length of experiments, the quantity of tubes tested, etc. It would be any statistician's nightmare. This is probably why we tend to draw conclusion from non-scientifc (by that I mean non-controlled and not statistically significant) observations made by many hobbyists.

That is why I figured if anyone would/could do it, it would be the tube companies. They didn't. Still, I see time and again, as if it were gospel passed down from on high that "DC is bad for tubes." Neo evidence, and lots of people are like Orwell's sheep and keep bleating "DC BAD! AC Good!" I am not a sheep, I guess. Maybe more of a Don Quixote.

I guess the point that I am trying to make is, it really doesn't matter whether tubes run on DC or AC. Being a hobbyist, I just do whatever is convenient and sounds good. I really don't mind changing tubes when they go bad, whatever the reason. It's a part of the hobby. Sorry, I am not being very scientific here, but neither is the amount of money I pump into the hobby so far. -Min

Exactly my stance. Even at $42 a tube, compared to the joy I get out them 6A5Gs are relatively cheap and sound great. If they die, I plug in another set of tubes. When the planet runs out og 6A5Gs, I will reire for 2A3s, etc. No worries.