ALL TUBES ALL THE TIME

Scastles · Post by **Scastles** » Fri Jun 03, 2005 12:12 pm

Aspen Pittman, penned it.

jps · Post by **jps** » Fri Jun 03, 2005 12:15 pm

Aspen Pittman.

jingle_jangle · Post by **jingle_jangle** » Fri Jun 03, 2005 12:21 pm

Aspen Pittman.

Scastles · Post by **Scastles** » Fri Jun 03, 2005 12:27 pm

Introduction by Spruce Goose. Think we've covered the authors name.

rictified · Post by **rictified** » Fri Jun 03, 2005 12:44 pm

Tap the pre amp tube with the amp on and warmed up lightly with a pencil, if you hear a ringing clanging or any sound like that it is microphonic and needs to be replaced. Brightness doesan't matter at all, if it works has the proper volume and is not noisy and not micropphonic you don't need new preamp tubes, they last a long time. I have had good luck with JJ Tesla tubes also. I have bought 12 of them within the last year for three SVT's and all sounded great and were quiet.
The Aspen Pittman book is good but don't take everything he says as gospel, it has a lot of nice pictures though. Rectifier tubes don't have anything to do with the sound they either work or don't so reliability is your only consideration when buying one of them.
Be careful with Chinese tubes.

ojobob2 · Post by **ojobob2** » Fri Jun 03, 2005 2:20 pm

Yeah, our fender twin reverb II had chinese "PM" tubes, awful things. Got it checked over and had the power tubes replaced with Sovtek 6L6's sounds amazing now

jps · Post by **jps** » Fri Jun 03, 2005 3:02 pm

There are a couple of other good books, "A Desktop Reference Of Hip Vintage Guitar Amps" and "Tube Amp Talk For The Guitarist And Tech" both by Gerald Weber of Kendrick Amplifiers.

www.kendrick-amplifiers.com

kevin · Post by **kevin** » Fri Jun 03, 2005 7:16 pm

I emailed Mitch Colby (VP at Vox/Korg) and he said he recalled the AC15-TBR preamp being all 12AX7 as well, but he wanted to check at work on Monday to be absolutely certain. At the very least, it would be all but one. I'd be EXTREMELY surprised if it called for both a 12AU7 and a 12AT7.

rictified · Post by **rictified** » Fri Jun 03, 2005 7:30 pm

12AT7 are the driver tubes in Fenders aren't they, I would think you'd need a driver tube in that also. A 12AU7 can usually be substituted for a 12AX7, you just get less gain.

kevin · Post by **kevin** » Sat Jun 04, 2005 8:06 am

The 12AX7, 12AT7, and 12AU7 are all pin-compatible tubes and are interchangeable, except for the fact that they each have different amounts of gain. The 12AX7 has the most, with a rating of 100. The 12AT7 is next with a rating of 60, and the 12AU7 is least with a rating of 20.

brammy · Post by **brammy** » Sat Jun 04, 2005 9:49 am

On the VOX AC-15 there is a handwritten label on the metal covering at each preamp hole:

DRIVER - VIBRATO & REVERB RECOVERY - REVERB DRIVER - 2ND PREAMP - 1ST PREAMP

As I said, I pulled out these Groove Tubes: three 12AX7M, one 12AT7 and one 12AU7. Why the amp tech had used two preamp tubes of much lesser rating than the others is a puzzle to me.... although there could be a good reason I guess.

So Kevin... it sounds like I wont hurt anything my going with 5 of the 12AX7 preamp tubes? I guess I'll give it a try and see what happens.

Any thoughts on the recifier? Should I stay with the Sovak?

soundmasterg · Post by **soundmasterg** » Sat Jun 04, 2005 5:47 pm

Sorry I have been away for a couple days from this thread and it exploded! On the AC30, a 12au7 is used for the tremelo, but I'm not sure about the AC15. I KNOW the AC15 doesn't use a 12at7, so that one is incorrect. Someone could have modified your amp and that could be why the different tubes were in there...or they could just have not known what they were doing too.

The rectifier tube is fine. If it works, (which it does or else you wouldn't get any sound), then just leave it in there. They last a long time and don't often fail. The Sovtek GZ34, as long as it is a real GZ34 and not a rebranded 5Y3 is fine. JJ makes a really good one too, and I have a Chinese GZ34 that came in my AC30 and its still fine now after 12 years of hard use.

The Groove Tube 12ax7M's are nice tubes, and relatively new, so I seriously doubt that they could be worn out. In fact, I would think that all of the preamp tubes are fine, and the rectifier tube also. I think you would be just fine if you got a pair of matched EI EL84's and put them in.

If you wanted to however, you could order a couple 12ax7's or various brands and sub them in and see how the sound changes. You may find it interesting and enlightening! The new JJ ECC803S/12ax7 has gotten very good reviews. The EI ECC83/12ax7 are good as long as they aren't microphonic. The EH 12ax7 and Sovtek 12ax7LPS both sound good and are reliable too.

Ok, I took a look at the schematic for the 1996 and newer AC15 and it shows 12ax7's for the preamp tubes, a 5y3 for the rectifier tube, and a pair of EL84/6BQ5's for the pwoer tubes. So get a couple more 12ax7's, get a 5y3 rectifier, and get a pair of EL84's, and you SHOULD be good to go. BUT, you may want to have someone check the amp out to make sure it wasn't modified to use these other tubes that were in it. At the very least, with the GZ34 in there instead of a 5y3,the voltages will be higher in the amp then they should be, and that could cause problems with tube life, poor sound, etc.

bill_yantz · Post by **bill_yantz** » Sun Jun 05, 2005 3:20 am

I did the GZ34 mod on my AC15 about 4 years ago. It has since gone as part of a trade for an AC30. The GZ34 in the AC15 provides more headroom and made a difference in my AC15 clean sound at higher volumes. But, you must increase the power fuse from 1amp to 2amp. I would never go back to the stock rectifier after experiencing the additional headroom on the AC15. However your application might be quite different, but something to consider and easy to do.

brammy · Post by **brammy** » Sun Jun 05, 2005 1:07 pm

Thanks so much to y'all for all this.... What I think I'll do is order all new EI tubes:

Five 12ax7's for the preamps, two power EL84

plus a 5y3 for the rectifier. I usually dont push the amp to high volumes, but I'll keep Bill's advice handy if there are problems with this setup.

ON the internet I did find this pix at North Coast Music for an AC30:

and this one for the power tubes (my setup didn't have these retainers but I will try to do so now):

On the chassis of my AC-15 the only text that I see that could be indicating the date is "AC15-62-00" which could mean that it was made in 2000. I bought it used about a year ago so I really dont know.

brammy · Post by **brammy** » Sun Jun 05, 2005 1:27 pm

byt the way.... what does "full wave" mean when it fomes to a rectifier? Should I get one that says that? or does it not matter?

On the same North Coast site is this pix of a retaining cap for a rectifier. tubesandmore.com doesn't seem to have any. My guess is that its not all taht important and only serves to keep the rectifier from falling out (which from what I can tell is very unlikely).