I just want to warn anyone who might be interested in the old metal cased vacuum tubes. I bought some and they work great! Sound isn't an issue. The issue is that after your used to glass tubes and a metal tube is sitting crooked, you go ahead and try to straighten it up. Yeah, it'll give you a nice good very hard shock. So don't touch metal tubes, they're positively charged, alot!
Quote by sickstring11
That's shocking!

Seriously, though, metal tubes? Haven't heard of them.
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They're pretty cool. I think they might be made for military radios for ruggedness. I got them from this guy: http://cgi.ebay.com/6L6-Tube-metal-/230391267198?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item35a463bf7e

Oh, and another thing. I think they might be over heating. You see, they wouldn't sit in the original sockets right because of the springy clip things. So I removed the clips and flipped the amp upside down so they could sit on there and not fall out. But after playing for a while, say 15-30 minutes it goes quiet and buzzing increases. I immediately shut it down when it did that. Let it sit for a bit, turned it on, and it worked for a while more. Do you think it's alright that they're upside down? Or maybe I should take the little covers off the 3 12ax7 pre amp tubes? Fans? I dunno, I need to figure it out by thursday or else the china tubes go back in for jamming.

Oh and the rust on the tubes is pretty badass, no? haha
Last edited by LeviMan_2001 at Jul 7, 2010,
yeah metal tubes were strictly for milspec gear.

see if you can find a datasheet for the metal version of the tubes. it'll tell you the mounting positions you can use. i'd venture to guess that it's the same as the glass bottles.
Well, to quote this data sheet for a metal RCA tube http://frank.pocnet.net/sheets/021/6/6L6.pdf 'The base pins of the 6l6 should fit the standard octal socket which may be installed to hold the tube in any position.' Well I have the chassis flipped upside down so they don't fall off (since I don't have those springy clips on there now). Maybe it's the pre amp tubes that are cooking, should I modify the clips so they will hold the metal tubes and then mount the amp the proper way?
Maybe you just smelled burning finger oil of the flesh? Tubes can do that I guess. How do they sound?
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i was just thinking about the fact that the cases are live. are you sure that's not a bad tube or smt? all the metal tubes I've ever seen had an inner layer of thick glass and none of the leads contacted the casing.

ah well if it works then so what.
Hmm. Well I put it back together in the stock configuration with the tubes up side down and the little grille thing on the back. Now it plays for longer before they go dull and buzz loudly. Perhaps the metal casing is insulating and causing heat to build up? It's too bad because it sounds just beatiful before it does that. Super low noise too.
Those are commonly used tubes are were used for a wide variety of applications, not just military.

They were an older series of tubes, prior to the fancy GC tubes.

TS you sound like you have no idea what your doing. All tubes are keyed, they can not be inserted at random. No active elements should contact the outside, read short. Go to a tech with a tube tester, he can test them and bias them in your amp if any are good.
Last edited by kurtlives91 at Jul 9, 2010,
Well if I wanted to take my shit to a tech I wouldn't be in GB&C. And don't look at me like I'm not like WTF about the active cases! I'll see if I can ohm it out and see which pin is connected to it. And yeah of course they're keyed. I should note, these have an extra pin compared to my regular 6l6's, that might be the case pin. I'll go look.

Edit: Sure enough, it's the pin that doesn't exist on the other tubes. I'll get pics up.
Last edited by LeviMan_2001 at Jul 9, 2010,
Here we are with pics

at least, that's the pin that's connected to the case, and as you can see, missing on the other tube (both china tubes are like that, btw) . And looking at that datasheet I posted up a few posts, it labels that pin as 's' I wonder if that's screen? If so, it says screen voltage is around 250. I guess that's why it hurt more than an outlet

And if you didn't guess, china on the left, ken-rad on the right.
Last edited by LeviMan_2001 at Jul 9, 2010,
The s does not stand for screen, I'm gonna guess that the metal jacket was meant to be used as a shield. If you were to ground it then it would help protect against interference. The glass tube version does not have this obviously.

So now as to why you are being shocked. It is possible that this pin is connected to another since it is not there on a glass tube version. Some boutique makers have a tendency to use some of the "unused" terminals on a tube socket to make building easier, all be it a bad practice. I'm willing to bet it is probably also done with some mass production amps as well. The other thing that is also possible is that your ground is not actually at a potential of 0 volts and that pin is connected to ground.
So do you think I should possibly disconnect whatever is going to it and put a ground on it? Also, if I threw some computer fans in there blowing on the power tubes do you think that'd make 'em run to cool or would it help keep them from overheating? At least, I think they're overheating when they do the go a little quiet and buzz thing.
Alright time for another doubble post! Whoo, I'm sure people hate that. Anyhow, so I popped it apart and it turns out greedy little Dennis Kager used that pin as a junction point for the resistors that attach to the heater (I think?) http://www.blueguitar.org/new/schem/misc_amp/pignose_g40v.gif see those resistors where they split off the 'Vb 406vdc' and roll on over to the 6l6's? Yeah those cross across my case pin! Damn it, so I kicked them out and hooked it up to ground. No real improvement except that it's much safer to operate around small children (and small amp dwelling gnomes). I didn't give it the 'go ahead an touch it' test though.

Now anyhow, all that said we still need to solve the whole overheating problem. I think that's what it is at least. What do you think UG? Are they overheating? Can I just blow a computer fan on it and call it a day?
wouldent a fan create a little noise in the amp though? like if your amp is by the telly or the fridge....
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It could. Also, what about bias. I'm not sure where I should probe to check it. Going off what this guy: http://www.clarkhuckaby.com/AmpMods/Pignose.html did, I think I should be testing Vf to make sure its around -43vdc? How would it be negative? touch the positive to it and the negative to ground and it reads negative on the multimeter?
Quote by LeviMan_2001
It could. Also, what about bias. I'm not sure where I should probe to check it. Going off what this guy: http://www.clarkhuckaby.com/AmpMods/Pignose.html did, I think I should be testing Vf to make sure its around -43vdc? How would it be negative? touch the positive to it and the negative to ground and it reads negative on the multimeter?

Thats what you want to do. You'll want to touch the negative lead to ground, and the positive lead to the top of R2, where it joins with R29 and R28. You can also do the same by checking the voltage just across R2.

Also, that isn't the heater line that the pin was used to junction. It was the High voltage line. The heater line would have probably been much more dangerous.
Your gonna run the tubes pretty hot with them being metal tubes. The metal version of the 6l6 cannot handle as much power as the glass version can. That being said, the pignose is a pretty compact amp so its going to run hotter as it is. If you don't get this issue with the glass tubes I'm willing to bet its because they can handle more power than the metal ones you have.
Well this thread is kinda fail with all the posting on top of myself and the "oh wait, I figured it out"s. But I think I've got it running right. I setup a bias adjustment like the guy did on the site, and it works. first time I hooked it up with the trim pot in a random place it was set right at -43v! haha Awesome. I also played it for about an hour and nothing happened so I think it's good to go. I'll stick a fan in there just for good measure later on but for now it works. And I got hooked up with a full set of baldwin organ 12AX7s for the pre amp stage ooooh yeah. I've yet to be able to crank it though so I can't really say how it sounds. But it's cool, I'm stoked.