WOW! I need tube help.

Nightfall

So I finally decided to try out the Raytheon 6V6GT/G and Holland Amperex 12AX7's I have. I was already using the same 12AX7 tubes I just wanted to test these out. I took all the tubes out and dusted off the preamp chassis and tube tops. I then put all the tubes back in using the new ones. I turned on the preamp and then POP! out of the speakers, this happened maybe two seconds after I fired it up. Startled the shiitake mushroom out of me. I VERY quickly turned the preamp off. I noticed that the Ratheon 6V6GT/G slowly lit up after I turned on the preamp up until the bang where it got brighter much quicker. What's the deal with this? The Raytheon tested better than NOS on Snows tester. I put the RCA 6V6GT back in and all is well, the preamp is fine and all eight tweeters are fine. Are 6V6, 6V6GT, and 6V6GT/G not interchangeable? The Raytheon has an extra pin that the RCA does NOT have.

I took this picture zoomed in too far to be holding the camera, I can't stay still enough for a crisp picture at this much zoom. The RCA is on the right, Raytheon on the left.



One last question: Is it a bad sign that a tube that is supposed to flash on startup stops flashing?

mhardy6647

I 100% don't know (sorry), but sometimes tubes have an "extra" pin -- and sometimes it can cause a problem IF a component manufacture happened to use that pin's location on the socket as a "tie point" for other circuit components. It's an admonition one will see sometimes in the tube manuals.

You do have a smatteing of receiving tube manuals, yes?

If not -- you do now:
http://www.tubebooks.org/tube_data.htm

Since I know there are folks here who know tube ephemera down to the individual tube*, I am sure you'll get a definitive answer 30 seconds after I post this drivel!

---

* to wit:

Yeah, that black plate triple mica halo getter pentode with the little smudge of a slpatted gnat just at the upper right corner of the screen grid was made by ol' Jimbo on Line 3 on a sultry Tuesday morning in August of 1953. Those things are sweet, man!

mhardy6647

FWIW, the 6V6GT/G designation is unknown to me -- probably top, top secret, Skunkworks stuff of its day

At any rate, here's what I was babbling about re: extra pins. The 6V6 might have an extra pin, per RCA manual RC-23. As shown, pin 1 is not connected to the internal structure of the tube (nor, apparently, was it connected to the metal envelope in the original, unsuffixed version of the 6V6).



Not sure a truly 'not connected' pin would be a problem, though.

EDIT: I cannot quite tell, on both tubes, where the base indexing pin is -- the RCA has six pins (which is "all" that is needed for this tube type) and the Raytheon has 7. I can't tell if the extra pin is at position 1 or not?

Basing convention is looking at the base (i.e., from below) -- at least, I think that's right!

heiney9

I can't say either since I've never had an issue. But what mhardy brings up is a good point. I use 6V6's at home in an integrated amp, and I don't remember seeing that extra pin in any of my old RCA gray glass tubes.

All 6V6's *should* be compatible (except the tall glass(coke bottle)which have a lower voltage limit than the GT or GT*), but with today's gear I'm sure there's bound to be an exception. Perhaps yours is the exception when using the tubes w/the extra PIN.

I'll go out on a limb and say those aren't compatible, but you might want to communicate with the gear manufacturer to find out specifics.

Again, rare instance, but it seems totally plausible in this case. Why Raytheon uses a 7 pin configuration is anyone's guess. Check over at Tube Asylum and see if someone has brought this up before.

H9

heiney9

As a side note you may have damaged the tube. Might have been some sort of short created by the extra PIN being tied to something in the pre-amp's circuit.

H9

heiney9

As far as the flashing Euro signal tubes, can't say on that either as I've never paid enough attention to notice the intensity or repeat ability of the flash on my tubes that exhibit a flash upon start-up.

If it stills sounds like it did when it was flashing, I wouldn't worry about it.

H9

mhardy6647

I just used the "Agree" button. Twice.



(the three posts above hit, I suspect, the various nails on their metaphorical heads)

mhardy6647

oh -- Nightfall -- how many 6V6s do you need, and do you need matched pairs or quads? I have scads of "old stock" (mostly not NOS) 6V6s of various flavors & I'd be happy to send some for you to play with if'n you want. Not sure anything I have'd be better than what you are using already... but I could see what's lurking in the basement if'n you want.

Nightfall

I emailed Dared. I do have physical schematics that Neil got from Dared when he upgraded the capacitors, if that would help. I posted it for Mr. Hardy in another thread one time because he was curious what a 6V6 was used for in a preamp in the first place. They're complete jibberish to me but I could post them again if that would help.

My preamp uses one 6V6, I have a clear glass RCA and a smoked glass RCA so I'm good on tubes. I got this Raytheon because Snow was doing a half off sale and it tested so good, thought it would be a good tube to have on hand. What can/should I do with it now?

I'm just thankful that the preamp or any tweeters weren't damaged.

Nightfall

This is what a poster on the Steve Hoffman forum thinks

They are the same tube and can be interchanged. The additional pins are not connected internally in the tube itself. I do not know what caused the pop. I would not attempt to use the Raytheon tube. It may be good, or something may have happened to it in transit. The problem may be an oxidized socket.

Just a guess what happened.. The pin connection to the filament may have been resistive. Resistance from oxidation, less current drawn may be the reason why the filament glowed less than normal.. there was a slight arc in the socket, and then full current passed to the filament causing it to glow more brightly just after the "pop".The arc in the socket is what probably caused RF noise to transmit into the signal path. (although RF noise should sound more like static)

I suggest to send it back to the seller... explain that you trust the seller, but the tube needs to be tested/ retested. Your amp is not the way to retest it.
Check your sockets. Clean them with a pipe cleaner and a little 3M finesse it, or automotive rubbing compound. Remove all traces of compound with ispropyl alcohol. Dry silicone lube is optional, which will help keep the socket free of oxidation. There's nothing like clean contacts for making your sound magical. (don't use deoxit, I do not recommend)

heiney9

Isn't the 6V6 used for the phono part of the pre? I forget on the MC-7P.

I hope you get an answer from Dared. I have tried in vain to get a hold of Bill O'Connell at Eastern Electric and I can't get him to answer an email. I still see he lists a few products on Audiogon so I know he's around.

Maybe it's just that tube.

Nightfall

I think it's used for voltage regulation? Don't quote me on that. The phono preamp uses the two right hand 12AX7's.

mhardy6647

Oh, yeah! I do remember that! It is probably used as a regulator indeed... but I'd have to go back & look at that other thread. As such (and I know statements like this are heresy around here!) all a tube in that application should have to do is work (i.e., I really, truly cannot rationalize 'rolling' regulators)... but that's just me

Nightfall

mhardy6647 wrote: »

As such (and I know statements like this are heresy around here!) all a tube in that application should have to do is work (i.e., I really, truly cannot rationalize 'rolling' regulators)... but that's just me

That was my understanding too, including the 5U4G rectifier, I was really just getting the Raytheon to have a very good long life backup on hand.

mhardy6647

ahh

6V6s are -- you know -- a dime a dozen.
I can probably send you a dozen if you want, in fact!

lightman1

mhardy6647 wrote: »

ahh

6V6s are -- you know -- a dime a dozen.
I can probably send you a dozen if you want, in fact!

On your dime of course, Doc.....
The lad has an affliction that puts swift demise on his purse and unsettled accounts.

heiney9

Rolling rectifiers certainly makes a difference. Never seen a tube regulator however.

Nightfall

mhardy6647

:-)

PM me if you want a couple-three 6V6 family member plinkers to try/keep as spares. Looks like it just uses one in the P/S, then?

Nightfall

It would seem Dared has no interest and/or time in getting back to me.

mhardy6647

Is mojo a factor of transconductance, or perhaps of the Miller capacitance?
I believe that the the top-end Hickok testers can measure mojo, but I am not absolutely certain of that. I believe that the mojo-enabled testers were US military classified during the Cold War era.

doctor r

The Hickok USMC-118 Cardmatic military cardmatic has a little door that has the the switch for mojo testing hidden beneath

mhardy6647

Well, if that's playing the Mojo Cardmatic, then we're playing the Mojo Cardmatic!

Nightfall

I spoke too soon, e-mail from Dared:

I guess not. It could be the bad tube though.

Which leaves me in the same spot. Guess not? What does that even mean?! Is that someone with a Chinese native language with bad English or a bad translation or are they literally guessing?

mhardy6647

Probably someone being honest (i.e., they don't know) -- sounds like an engineer.
Not, e.g., an MD. You know the MD's motto, yes?

Sometimes in error, never in doubt

(and I say that without a trace of rancor; sometimes the best thing to do is just make a decision & get on with it -- especially when a life hangs in the balance)

heiney9

Just throwing it out there, a bad tube can still measure fine on a tube tester. Depends on what you are testing for and where the tube is failing. I say "can" and not "always" or "never".

It is possible the tube is bad, but it wasn't caught when testing. These little glass bottles are 50-60 years old.

H9