Replacing 12au7's

[Keim]

One of the tubes in my Bottlehead Foreplay pre-amp went out yesterday. I'm looking to replace it, and have a few questions:
1. Do I need to get a pair-or can I just replace the one?

2. If I do need a pair, do I need to get a matched pair?

3. Where are some good places to get 12au7's (or equivalent)?

4. What is a fair price for Mullards or RCA clear tops? And, what are some others that are popular?
Thanks for answering my questions!
Darrell

[Sckott]

RCA Clear-tops are very good, and a pair in decent shape are found for about $50/pr but sometimes less. Mullards are very good, but you don't have to bother... Not worth the stress.

I have a pair of Mullards used on one, and a pair of RCA clear tops on another one I built from my own brewed Foreplay. Hint: Better caps make a better Foreplay and at great value.

I do have a bunch of 6189 RCA green-printed tubes that are absolutely wonderful. I love this tube! Black plates, wonderful sound, sturdy! I can sell a pair cheep! I bought a pack of 5 at once. I just don't want to give up all 5 :)

What tubes did you have in your unit? The midrange OEM Philips? Did they have blue lettering?

Matched pair: No. It's a self biasing amp. It's just best that you get a pair that are equally strong, but it does not have to be matched.

[stereo71]

Sckott is right on here. I have also used various
equivalents to the 12AU7 in my Foreplay, such as
the 5814A (found some nice Sylvania gold pin ones),
some GE and RCA 5963. Some prove more microphonic
than others--might be due to the Foreplay's top
plate. But feel to experiment! Check the forun
on Bottlehead's site.

--Roger

[Sckott]

Yes, my 6189's are more microphonic than other tubes, but I love them just the same.

I meant to say, the RCA clear tops and the Mullards didn't yeild a big taste-test difference. I forgot to add that.

That being said, there are a lot of very nice tubes that you can roll into this circut, all doing plesant, different things. The Foreplay is a wonderful toy. I enjoyed making my own "brewed" Foreplay from spare & bought parts.

[Ambel]

It's my least favorable tube but I like using Telefunken 12AU7 and Sylvania
5693 Gold Brand gold pins.
I have used Mullards, Amperex, RCA clear tops.

[Keim]

Sckott,
The tubes I am replacing are GE. They sounded good-hated to see one die! But, now I get to try something different. If you're interested in selling a pair of those 6189 RCA green-printed tubes-I'd like to know the price. Email me keim@moscow.com. They're a drop-in replacement for the 12au7's, right?

[Steve Hoffman]

I've never really found a yummy 12AU7 tube.

I have samples of almost all the good ones, going back to the 1950's, but none really knock me out.

Ironically, the Telefunken 12AU7 really stinks IMO. Slow, groggy, bloated, just lays there (like my ex-girlfriend). I just hate that little sucker. Since the Tele 12AX7 is the best of its kind, bar none, I was truly disappointed in the 12AU7.

Oh well. :)

[Sckott]

Originally posted by Keim
Sckott,
They're a drop-in replacement for the 12au7's, right?

For the record, yes they are. Merely slip these in.

[Joseph]

Originally posted by Steve Hoffman
I've never really found a yummy 12AU7 tube.

I have samples of almost all the good ones, going back to the 1950's, but none really knock me out.

Ironically, the Telefunken 12AU7 really stinks IMO. Slow, groggy, bloated, just lays there (like my ex-girlfriend). I just hate that little sucker. Since the Tele 12AX7 is the best of its kind, bar none, I was truly disappointed in the 12AU7.

Oh well. :)

Steve, what good tubes can be used in place of 12AU7's?

[petzi]

I chose a Dutch made ECC82, branded Valvo, which was also sold under the names Philips, Amperex, Mullard, etc...

ECC82 is the exact European equivalent of a 12AU7.

I have some Siemens E82CC which are military grade, but I haven´t listened to them im my amp so far.

Regarding Telefunken, there are ECC802S and ECC82 tubes, the ECC802S is a very expensive low-noise, long-life tube, and quite different from a ECC82. Both are replacements for 12AU7.

[Dave]

As a non-tube owner (not for ever mind you;) ) I'm a little confused. Can the 12AX7's replace the 12AU7's? Are they both input tubes?:confused:

[Sckott]

Dave, Read this:

http://store.yahoo.com/thetubestore/gainfactor.html

[petzi]

Originally posted by Dave
As a non-tube owner (not for ever mind you;) ) I'm a little confused. Can the 12AX7's replace the 12AU7's? Are they both input tubes?:confused:

Never ever replace a tube with a different type. It will not operate correctly. The circuit was never designed for that. If the engineeer had wanted a 12AX7 tube, he would have chosen that for his circuit. You would have to redesign the circuit for that to work correctly, and you´d need a good understanding of electrical engineering with regard to tube circuits to do that. If you want to redesign the circuit, you should have chosen a different amp in the first place.

If you just replace a tube with a different type, it might fail soon. Tubes, in particular vintage tubes, are too expensive for experiments like that. Some of the "tweaks" posted to the Internet are irresponsible from that point of view.

"Gain" is not the only thing to look for. A tube needs a proper operating point for it to function correctly and to live long.

Of course you can always replace a 12AU7 with an ECC82 and vice versa, because these are just different names for the same type of tube. You can even replace a 12AU7 with a ECC802S or E82CC, because those are upgraded special quality versions of the same tube. In the US nomenclature, they would probably be named 12AU7WA.

[Dave]

Thanks Sckott and Petzi. Wow there sure is a lot of things to know about the tube endeavers.

[Keim]

As an addendum to this thread, I did buy a pair of 6189 RCA green-printed tubes from Sckott. They sound very nice indeed. Much better definition in the lower end then my original ge's. I was also quite surprised by the difference in amplification. The RCA's have a fair bit less-still plenty, though! They've only run a few hours-I can't wait til they're burned in.
Thanks Sckott!
Later,
Darrell

[Sckott]

Glad I could help! I was suprised when I first used them. I keep one in my PH-1 Phono Pre, and the rest, I kept for a rainy day. Very nice tubies, and at the time I rolled quite a few, these stood out strong suprisingly. :)

Enjoy!

[Drew]

I had mentioned about six months ago in this forum that bought some RCA 6189's in an ebay auction but didn't realize that I should be looking for green lettering. I was disappointed at the time because they were very microphonic and also bought some JJ 12AU7's from www.thetubestore.com to replace the originals that came with the Foreplay kit (I think they were from Penta Labs but can't really remember) and used the JJ's for several months. Well, I went back to the microphonic 6189's a few weeks ago and realized that they're much clearer. The JJ's sounded like the music is in a fog. I just have to keep the Foreplay in a place where its isolated from any vibration.

Someone is a forum somewhere (maybe this one) suggested Amperex 7316's for use as a 12AU7 substitute. I don't know how they sound but they're might expensive on Ebay or Audiogon.

Kiem, do you have the basic Foreplay or do you have the constant current source upgrade?

[Keim]

Drew, My Foreplay is slightly modified. Its got the full meal deal package from diycable.com (love those Auricaps!), gold rca's, 6 inputs (instead of 3) and c4s. How about yours?

[Drew]

I just have the constant current sources installed. I purchased the stepped attenuator from for the volume control, but haven't installed it.

I have other DIY project's on the drawing board. I thought about upgrading the output caps but haven't gotten around to it yet. Did the Auricaps make that much of a difference? In what respect?

I've been experimenting with simple one stage tube preamps circuits which use 12AU7, 12AT7, 12AX7's (bought some telefunkens but didn't have anything to plug them into), 6SN7's. Here's a cool page that has been a great guide:

http://www.users.globalnet.co.uk/~valveamp/LinePreProject.htm

[Keim]

The auricaps helped provided a better sense of detail-it became easier to "see" where the different instruments were located. Does that make sense? They also helped with the lower end-better bass. In my system they made about as much difference as the c4s.
What's your amp?

[Drew]

All makes perfect sense to me.

Bottlehead Paramours with the c4s installed. I finally put the info in my profile.

[Keim]

I've got Paramours myself. I haven't put in the c4s yet. What was their effect? Any other mods on your Paramours?

[Drew]

Unfortunately I put the c4s's in before the breakin was complete so I'm not really sure. When I first had it all hooked up without the c4s's I had a very hollow sounding lower midrange. A few people in this forum knew I was going DIY and asked me how it was going and they could probably tell I was hedging. :D After about 2 weeks I put the c4s's in... and it didn't change much, maybe the bass was a little tighter. I had been playing it all day on my days off from work and 4 or 5 hours a night the rest of the time. Wasn't confident enough to let it run while I was at work.

I had it hooked up to my pc one night as I was watching a DVD and everything sounded pretty good. Connected it back to my CD player and everything sounded like magic. I demo'd it for a friend with Steve's remastered Door's L.A. Woman and his comment was that the tone was so perfect it was scary. I'm mean I might be missing the very lowest octave but everything else is there in spades. Upgrading to the better Magnequest output transformer might give me more of the lowest bass but my speakers don't go down much under 50 Hz. I'm an apartment dweller so if I had that I'd just get the cops over anyway. I feel like I can reach into the speaker and grab the guitar out of Joe Walsh's hands in Hotel California. I never expected it to take a month to break in. I think the breakin was in the output transformers, but I could possibly be wrong. I was expecting a couple of days. I haven't had anyone come over and tell me there were any glaring faults, and from most of them the first comment is "I could listen to this all day." This is music delivered with finesse, but it doesn't lack detail at all.

The only upgrade/experimentation I've done with the Paramours since then was rolling in some Sovtek 2A3's in place of the Valve Arts that came with the amps and I definately prefer them. Much smoother in the treble.

I'd like to try some of those TJ Mesh Plates 2A3's Bottlehead sells but at $275/pr its going to be awhile. NOS RCA's? Gonna be a long time before that day comes. Too many other projects.