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Russ57's post responding to mine got me wondering... he mentioned using 6CG7s in a 12AU7's socket. I looked it up with the TDSL program (don't know what it stands for) and that tube isn't just not a replacement for a 12AU7 -- it's got a different pin-out, too. How did he/general knowledge stumble across the 6CG7's being a perfectly good substitute for a 12AU7?Is it just a matter of trial and error and best guesses when it comes to preamp tubes, or is there a method to it? If it is, it would be awesome to get one of those cracking huge lots on eBay and start plugging every nine-pin miniature I can find in to see if it works. But I know it can't possibly be that easy, and I really don't want to fry my equipment. I've also got the feeling that 95% of those lots are worthless crap, but whatever.
I'm looking to be right adventurous in all this, but not stupid. Thanks.
Follow Ups:
Get the Tube Substitution Handbook. There is a lot of misinformation
posted on the net.
You have to refer to the GE ESSENTIAL CHARACTERISTICS ELECTRON TUBE DATA BOOK. You have to survey each tube footprint and pin out, transconductance, mu, plate resistance. You have to know what the JAN military equivalents are. There is a website; Frank's Electron Tube Data Sheets;http://frank.pocnet.net/
"I take you as you are
And make of you what I will,
Skunk-bear, carcajou, bloodthirsty
Non-survivor.
Lord, let me die but not die out." THE LAST WOLVERINE by James Dickey
...absolutely sure that it was a safe replacement for my circuit.For a 12au7, there are plenty of direct replacements; in my circuit 5814, 5963, ecc82, 6189, and others. However, some of the subs used by others do not work in my circuit and put components like the transformer at risk.
If you want to sample some 12au7 (ecc82) flavors; I (personally) wouldn't buy one of those '50 untested tubes in a bucket' lots. There's a lot of work involved in testing, matching and culling those lots; although, some find that fun. I've tried a few of those lots and often ended with surprisingly few pairs. It's a different matter if they're all RCA 5963 black-plates, for example; that is if you want 15 pairs of RCA black-plates.
I would sample some of the pairs offered on ebay to get a feel for the sonic signature of each flavor in your gear. Maybe start with a search here on favorite 12au7's and work from there. You can get a lot of good tubes at $10 a pair, or less.
Actually my best friend.
I gave him four nos Mullard gold pin 6922's because he stuck by me during some hard times and does to this day.
He plugged two of them into the 12AX7 sockets in the phono stage of his pre. When he heard crackling and popping, he turned the unit off. Then thinking there was something wrong with the tubes, he plugged the remaining 6922 pair into the 12AX7 sockets again!
He realized what he had done and called me on the phone. There was not much I could do about it at that point.
I gave him four new Amperex 6922 oranges (green/yellow box) and told him not to hurt himself!
Thanks.I'm really, really glad I went out to the shop today. The Electro-Harmonix 12AU7s probably aren't the best thing out there but in the Foreplay, they're damned near the best thing I've ever heard, solid-state included. Again, I'm not wild about their 12AX7s, so I was expecting to be underwhelmed. The only other tube the store had was JAN Philips, the only pair of which I've heard (6922s, actually) had basically been like the Eis: they're not lacking in anything, but they don't really have anything going for them other than being perfectly satisfactory. It's clichéd as all hell, but the EH tubes seem to have removed a layer of murk that I had never noticed before: I'm literally hearing little licks and flourishes buried in the mix that I've never noticed; everything is completely crystal, and there's a hell of a lot of bass without the unnatural boomy feel of the bass-boost function on cheap portables. Perfectly natural-sounding, which is a bit funny because it's lower-fidelity and all.
The Ei tubes are Yugoslavian; I've seen their tubes specifically advertised as "Ei Yugoslavia" so I'm guessing there's some other factory or daughter company. I'm not sure if it's referring to the small Yugoslavia that changed its name to Serbia and Montenegro, or if it's greater Yugoslavia, the country that split up violently in the early '90s. They sound a bit watery, weak, and unengaging, although finely detailed. The EHs are every bit as detailed if not more so, with much *more* of everything all across the band. They were magical over speakers right away, but I didn't like them with headphones at first... they were a bit too forward, too aggressive, so I switched back to the limper Ei tubes for night listening earlier this evening...
When I had listened for a bit, I put on a Spacemen 3 disc on repeat at low volume and by the time I woke up from my nap, the tubes sounded absolutely wonderful with cans. This could be my refreshed head, from a proper extended warm-up, or just a little bit of burn-in. Whatever the cause, they've had about six hours on them already and have just gotten better over that time. This can't be the final word in this sort of tube... if it only gets better from here, it's going to be a great journey.
I also just bought a third pair of tubes for the Foreplay, and with that I'm going to give the buying a break for a while. But they were cheap ($8 apiece with free shipping) and it was a chance for a third opinion, as it were... and it really is something different, because the seller misstated what they are. The tubes were advertised as GE "5965/12AU7", but it was only after I had bought them alreaday that I looked them up and found that a 5965 isn't a substitute for a 12AU7 after all. 5965s and their cousins 12AV7s are supposed to be safe in the Foreplay, thankfully. All's well that ends well, I guess, and it'll be interesting to have a different type as well as a different brand (and also an NOS brand, although the Ei Yugos might be used old-stock), even if that was a mistake. The GE 5965s are supposed to be pretty good, too. Yay.
Wow, that was a long post. God, I probably come off as the biggest ditz in the world... I feel like I'm falling in love, literally, and I'm acting like it. Jay-sus. I'll get better.
Here are a couple of good links that this moron has found useful...12AX7 review to supplement Joe's - http://www.audioasylum.com/cgi/m.pl?forum=tubes&n=175982&review=1
Is it "safer" (that is, less stupid) to be more reckless with sticking any nine-pin miniature tube into that socket? I've searched this board, of course, and discovered that Very Bad Things can happen if you replace certain power tubes with other power tubes, especially if you don't adjust for the bias.But provided that preamp tubes area so dinky in comparison, do they pose nearly as much danger to your person/gear?
Forgive me if I, in any way, gave you the impression that it was okay to plug any old tube into any socket in which it would fit. That is not the case at all!When I mentioned picking up a lot on ebay I was talking about a lot of assorted 12au7's.
With regards to the 6cg7 swap....go to tdsl and look up the 12au7. Down at the bottom of the page pick the link for Dave Crittle's site (retrovox). Read the second paragraph on the first page of the tube data sheet. It states the 12au7 is very similar to the 6sn7. The 6cg7/6fq7 is a 6sn7 in a nine pin mini bottle. The only difference in pinout/wiring is your 12au7 has pins 4&5 tied together and one heater wire there and the other heater wire on pin 9. To convert remove the jumper between pin 4&5 and attach the hetater wire on pin 9 to the vacant pin, either 4 or 5. Repeat, the heter wires for the 6cg7 are pins 4&5. But be forewarned the 6cg7 needs twice the heater current and I don't know if the foreplay 2 has the ability to handle it. The foreplay 1 didn't but the foreplay 3 does.
Also, if you check the bottlehead forum you will see the 6cg7 conversion is quite popular. I have heard it and can vouch for it being an upgrade.
In time you will learn how to look at data sheets and determine if another tube could be suitable. And of course there are places that list subs. In general it is best to ask the company that makes your gear and not to blindly trust others....including me:) Info on the web isn't always to be trusted and even tube data sheets have errors!
Forgive my cluelessness as a tube naïf! I decided to not even try substitutions or exact matches, but just stay with the 12AU7 proper until I get bored... holding off on NOS until I make the rounds of current-runs as well as I can.I just got back from a guitar shop and, uh... the Electro-Harmonix tubes kick ass. I wasn't all that impressed with their 12AX7 but the AU is stellar. The tubes that came with the Foreplay were a pair of Eis and were entirely, skull-crushingly pedestrian. I knew there was better out there because they couldn't get much more MOR, and I found some better ones. Hooray. Great buy.
If you don't care to post that in public email me at rbrunt(at)mercymiami(dot)org. Perhaps I can suggest someone in your area to hook up with.You really should head over to the bottlehead forum. A lot like RCA cleartop 12au7's (too bright to me). The brimar (forget the number) is a big time favorite. Personally I kinda like the siemens. My 2 buds both have foreplays so I have heard a buch of tubes in them. But neither have the foreplay 2. And yes, you want to use the foreplay if you possibly can. Properly tricked out it kicks the crap outta the other stuff.
And hey dude, don't worry about coming off as clueless. That is what we are here for. You can't learn if you act like you know it all and don't ask them dumb questions now and then:) So ask away and feel free to email. I am glad to explain things. And ofcourse do search the archives here before asking them dumb questions for tons of great answers. Ditto on the asylum FAQ's
Russ
P.S. Ei made a killer 12ax7 in the past but quality control went to shit about 3 years ago.
...RCA clear tops, RCA 5963 black-plates, Tung-Sol 12au7a's, Toshiba 5963's and ecc82's, and various three-mica 5814's. It's also fun to try some of the relabeled organ pulls (Conn, DuMont, Baldwin, etc). Of course, then you can get into the real esoterics wih price to boot (is the next 10% worth 3 times the price?). Lots of value and enjoyment in the basics!
And more, here:
Yes they do. If you look at the tube data you can tell if two tubes have the same pin out. You can also tell how much current they will draw in your circuit and what the gain will be, etc...Tube swapping (between different types) is not done "willy-nilly".
The 12au7 and the 6cg7 are very close and are (for the most part) electrically interchangeable but that doesn't mean you can just pull the 12au7 and jam the 6cg7 into the socket.
Do not install a tube unless you know for sure that it will not burn up your unit.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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