Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: dude on August 26, 2010, 12:29:18 pm
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Brand new Raytheon NOS 6V6
Plugged it in, pull half of it out.
I could lengthen the legs a bit but which leg goes where...?
Pitch it...?
al
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I'd pitch it, BUT if you want to do it, just follow the legs up inside the tube, one of the connections to plate, screens, cathode or heaters will be obvious. From there use the data sheet.
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Really odd. Never saw that before, even on WW2 aged tubes.
The other day, I was stripping parts from a piece of surplus junk.
(http://i172.photobucket.com/albums/w32/ttm4/3x.jpg)
Pair of nice heatsinks, 8 qty power transistors on a board. Clearly, these were flow soldered when built.
On one of the boards, each and every solder connection to the pins of the transistors was cold soldered. After I removed the two mounting screws for the transistors, I applied very slight "away" tension to the heat sink. ALL FOUR of the transistors simply fell off the board. Although the soldered connections to their pins certainly appeared to be sound, the solder had simply encased the pins and was making no nominal connection whatsoever. Never saw that before either.
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You should be able to get continuity between pins 7 & 2 = filament. Knowing those pins will allow you identify all the others.
Try to move/disturb those wires coming out of the glass envelope as little as possible thought it MIGHT behoove you to scrape them gently with a knife blade and tin them before trying to reinsert them into the tube base. Also, get ALL the solder out of the tube pins before trying to reinsert the wires pin-by-pin. Here's where a soldersucker is a fantastic tool.
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Those ends with the insulation, would they be the plate and a screen grid..?
I'd like to save the tube, it's from a matched set. I guess one would have to know what's a plate look like inside a tube, I sure don't, just a schematic.
I've search around but can't find a site that shows what's what inside a tube. Anyone know of one?
Thanks as always.
al
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I doubt they crossed wires inside of the base. I suspect there are 4 wires, a space, 2 wire, and a space to complete the circle. Pins 2 & 7 = filaments and they will ohm out to each other. (From the outside in) The plate is the only visible (mostly anyway) element of the tube. It's the big outside metal part. Next is the supressor grid (G3), then the screen grid (G2), then the control Grid (G1), then the cathode, and right down the middle is the filament. Here's a diagram.
(http://www.r-type.org/static/ef91diag.jpg)
Clean all the cold solder out of the base. Carefully clean the leads. They probably have enamel insulation so an exacto blade may be in order. Slide it together. With a wet iron tip, heat the pins and flow solder in through the holes in the ends of the pins. After it cools, you may need to dremel grind a little excess solder off the pins. If you glue the base to the bottle, use something rated for high temps. Test the tube before you use it.
I wouldn't rely on this tube whereas it's already failed once. It'd be a good little fixer upper project. If it does work, keep it around as a "beater" test tube (pun intended).
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With modest effort, you'll be able to reason or trace or see out the paths of the wires out of the envelope into the base.
The biggest challenge, as I see it, is to glue the glass envelope to the plastic base effectively. I don't know of an appropriate adhesive, offhand.
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Thanks, the diagram looks easy enough but no sure thing.
One more thing, if I screw up and probably a stupid question, now I'm giving away my lack of electronics education, no chance of the glass breaking when I pop it in the tester? I think the specs in the tester use 45v for grid and 55v for the plate.
As far as the base, I've had good luck with super glue on loose bases. I don't know the temp rating but it sure flows down inside a loose base and tightens the base nicely. I have done this several times and never had one come loose even after months of heat.
Since I'm a USA tube freak, I've learned to to pull the tubes out by their bases and not the glass. :grin:
I'll give it a shot.
al
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Mmmm, on a hot tube like a 6V6 I would have to be concerned that the heat would soften the super glue and you might have a stinky situation, if it gets hot enough. Super glue effectively turns into low-temp plexiglass when it hardens correctly, doesn't it? Check the specs of the hardened glue. Yes, It'll flow real darn good!
You might be better off using some higher temp-spec rated epoxy.
I don't think there's much chance of the glass breaking putting it into the tester, but if it were me, I'd wear a glove rather than risk jamming broken glass into my thumb.
I just do not know how durable a S-glue joint would be under heat-cool-heat-cool. Just don't know.
As I said, I don't quite know WHAT type of glue is proper for the circumstances.