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Scoring an NOS (U.S.) Tube Score???

4/26/1999 4:05 PM
Scoring an NOS (U.S.) Tube Score???
Help Mr.Wizard!!!!!!  
(I don' wanna be a TubeHead anymore!!!!>>>>>!!...)  
So, I took the plunge, and there I am in the middle of a warehouse packed with electronics overflow, new and old, and looking at the shelves on shelves of faded-package firebottles, numbers limitlesslike the stars, the firstone I pickup (randomly) if 6V6. "Score!" This must be a sign from the Goddess!!!  
Then reality sank in, and I, green as the spring grass and armed with nothing more than a desire to learn to build tube amps, am faced with the insourmantable task of deciding what to take a chance on buying. I would like to stock up on anything that would come in handy down the road, building a variety of valve-driven gear, Marshall or Fender style amps without attatchment to dogmatic traditions. The price is certainly right ($1 a pop if you dig them out yourself) so I don't mind being a little careless, but I do want to get valves that will be usefull in future audio projects.  
"Tube data" you say, "right here on Ampage?" Well,that, the tubestore listings and the Duncan TDSE charts all just left me more or less confused.  
Isn't there a site which lists all the most common (audio)tubes and the alternative or military-spec numbers which are appropriate substitutions, or is this a vast network of info the still only is accessed by experience?  
And, is this, in fact, how the Duncan pages are set up? Say, for example, the 6AQ5's. (I managed to score a few of those). Are they straight substitutions for the 6V6??? Or do the actual spec sheets give more detail on conversions?  
Why can't I see a listing for a classic rectifier tube like the 5U4 on either of these two resource pages. 7025's for the pre-amp? Surely that's in Duncans archives? I don't see the # on the scoreboard. I've been known to miss things, but i did scour the index.  
How about subtle marking variations? Are they often a good indicator that it is closely related to another tbue, say,like the 12AT6 as opposed to the 12AT7 or the 6BQ6GA(6CU6) to the 6BQ5? What about Tung-Sol and Raytheon, are these reliable tubes in thier time??  
Just in case there's still someone reading and curious, I'm gonna throw out list of some tubes, and if you know any substitutions for common tubes, or cool projects they could work in that don't involve pyrotechnics or popping glass, well, feel free to clue us in. Many generations of tubie-newbies will thank you.
" (PHILCO)  
6CD6/GA (Is GA a relevent marking)  
6AV5 (GE)  
6K6(A4B) (SYLV) (fender reverb tank?)  
6BQ6/6CU6 (TUNG-SOL)  
12AT6 (RCA)  
12SQ7 (RCA)
... We now return control of your Ampage network to you .....  
4/27/1999 11:21 AM

There are a couple tube substitutions handbooks avail from AES etc.  
You can go from US>>Euro>>Mil etc.  
meanwhile, 6AQ5 <> 6V6 ever. SPec sheets do not give conversions. You can read the specs though and determine what will need to be done (or if indeed anything can be done)  
Generally, the code on a tube will go Filament volts, 2 letter code, # internal connections (ex heater) and then a suffix code. Example:  
12 (12 V heater) AX (type code) 7 (7 elements, I guess the heater center tap counts as 1?) so 12AT6 has a different internal structure.. (6 elements).  
12AT7, 12AU7, 12AY7, 12AX7 all have the same heater hookups and # of elements. A good sign, but no guarantee of compatibility. You need to do the grunt work of looking them all up and comparing specs. Another example, the 6EU7 is essentially compatible with the 12AX7, but it has a 6.3V heater and a different pin-out. You can sub one for the other with some work..  
Suffixes: Early power tubes had "M" suffix (metal), then "G" (as in 6V6G) which meant Glass envelope, then GA (the next revision). GB, and sometimes even GC (as in the 6L6GC you see in Fenders). Many of these tubes began life in the mid-late 1930's, so a few improvements along the way were bound to occur. :-) "W" was a "rugged" suffix given to tubes which generally had thicker mica spacers etc for high vibration environments. Many common tubes had mil spec equiv versions, like the 6L6GB had the 5881 as it's mil equiv. Sovtek called their tube the 5881WGT. They were trying to evoke the notion of a ruggedized mil-spec tube. (ie: marketing). Not slagging the tube or them (heck, I use them!!) , just by way of explanation. The suffix "Y" often meant a low loss base was used (for RF apps generally). Pre-amp tubes got sufffixes as well (12AX7A for ex)  
Tung Sol was one of the best mfrs. Tung SOl 5881's were the stock tube in the '59 Bassman, or so legend has it. I have a pair in my 2x10 super, and they are pretty special IMO. Raytheon is also an excellent mfr.
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4/28/1999 11:40 AM
Re Tube Elements
Thanks, Speed  
I can't tell you how much it means tohave the conceptslaid out invery simple form like you have so iften done for the newbies. Believe it or not I do read books, resources and sites on the various subjects, but sometimes the most basic questions still evade a thorough understanding.  
So, to be REALLY basic, when you talk about the number of elements in a tube, does that directly and always correspond to the number of pins?  
Go, Speed, Go!  
4/28/1999 1:14 PM
Reid Kneeland

"So, to be REALLY basic, when you talk about the number of elements in a tube, does that directly and always correspond to the number of pins?"
Nope. The 12A*7 tubes, for example, all have seven elements and nine pins (there are three pins connected to the heater).  
4/27/1999 11:57 AM
Re: Scoring an NOS (U.S.) Tube Score???
"Isn't there a site which lists all the most common (audio)tubes and the alternative or military-spec numbers which are appropriate substitutions,"
Yes, there is. There is such a section in the Tube Amp FAQ under "Substitutions". See the" target="_blank">">the Tube Amp FAQ at GEO.  
It isn't exhaustive, but all the more common ones are there.
4/30/1999 11:07 PM
Ned Carlson

The Duncan site really does give most of the subs, but if you've got the GE tube manual, it lists everything that's got the same pinout.  
I'm not terribly fond of tube substitution books, I've ranted at length on RAT about some  
of the more offensive errors.A good tube manual like the GE lists most of pertinent data so you can usually tell what'll work.  
There's still a few odd ones like 6CZ5 for 6973 that are hard to find because the pinout's just slightly different.  
I don't know if you're typing in something wrong, or if you've got some kinda Netscape or IE bug (that's been known to happen, I think he may be using Javascript) but there's a metric buttload of links to info on 5U4's on Duncan's page.Same for 7025.  
If you just can't make it work, the HB-3 pages on both of these are on our page:  
6AQ5 is supposed to electrically equivalent to 6V6 *within the ratings*. RCA said so, and RCA never lied (gag, snort) ;-) But the socket's different.  
Similar tube numbers can be quite different,  
a 12AU6 has not much to do with 12AU7. As pointed out elsewhere, the first two digits usually are the filament voltage (except for loktal tubes), the last two after the letters are the number of elements...but 12SJ7 ain't nothing like 12AX7 at all! And it doesn't apply to some industrial types, 2C51 doesn't have a 2 volt filament nor 51 elements.  
Four number tubes are worse, changing one digit can change it from a submini mic tube to a 2 million watt monster tube!  
6AU6 gets used in radios and some old guitar amps. A pentode.  
6AL5 gets used in compressors.  
6CD6 can be a nifty output tube, 50 and 100W DuKane amps used them. There's a diagram for one at  
GA means it's got a smaller bulb than the G version.Works the same otherwise.  
6K6..yeah, reverb units.  
12AT6 and 12SQ7 have triode sections that could be used like half a 12AX7.  
5AU4 is like a 5U4 but draws more filament current.  
6BQ6 and 6DQ6 are sweep tubes for b/w TV's, which could be used for output tubes, but I've never tried it.We have the plate caps for these.6AV5 is in a similar vein but no plate cap.
5/1/1999 10:48 AM

>>6AQ5 is supposed to electrically equivalent to 6V6 *within the ratings*. ..But the socket's different. <<  
This is the crux behind why I said they're "not equal".. Between re-socketing the amp in question, and finding a 6V6 guitar amp that is running anywhere near the specs a 6AQ5 would need, I don't see it ever happening. (the Fender musicmaster bass amp not withstanding)  
I tend to think of substitute tubes as ones that don't require rewiring, drilling, punching or a reworking of fundamental amp parameters (like B+). At any rate, I did not mean to mislead or misinform. eg: you put it a lot better than I did. :-)
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