Cleaning up a Deluxe RI - 12AT7 or 12AY7?

Chris LeDrew · From: Canada

I can't readily put my hands on a 12AY7. Will a 12AT7 clean up the headroom a bit on this amp? I don't know a big lot about tubes, but I was told an AY7 is good for getting more clean headroom. They seem pretty rare compared to the AT7. What is the difference?

Thanks....
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Greg Simmons · From: where the buffalo (used to) roam AND the Mojave

Chris;

one of the resident toob gurus while no doubt chime in, but in the meantime Mike Kropotkin has some good info on his site...

http://kcanostubes.com/content/newsletter_details.asp?ArticleID=4

http://kcanostubes.com/content/newsletter_details.asp?ArticleID=5
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Jon Light · From: Saugerties, NY

edited..........oh man, I'm such a dweeb----I posted the exact same links as Greg. But I thought of them first!
Doesn't totally answer your question but it gives a good overview of the gain properties of the tubes.

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

In a word, yes - they have a lower gain. I wrote a post a couple of years ago comparing nominal gains of a bunch of dual-miniature preamp tubes: http://bb.steelguitarforum.com/viewtopic.php?t=64201

Overall, I tend to like 12AY7 or 5751 better than 12AT7 - for some reason, I have found 12AT7 to sound a bit thin. In Fender amps, 12AT7 was typically used only for the phase inverter (power tube driver) and reverb send, and I always assumed there was a reason for that.

Online tube sources like Angela Instruments - http://www.angela.com/ - certainly have 5751 and 12AY7 tubes - they're not cheap but not ridiculous, IMO. 5751: 80's NOS JAN Philips/Sylvania are $19, 80's NOS GE are $29; 6072/12AY7: 80's JAN Philips/Sylvania are $36.

You can also see from my comments on NOS tube prices two years ago that a lot of these tubes are definitely increasing in price.

BTW - you can see from my chart that 12AV7 tubes have a nominal gain of 41, as compared to 45 for 12AY7, and Angela has a few of these at $10 each. But most people I know argue that they aren't great for tone-generating circuits. Seems like I tried this years ago as a sub for a Tweed Bassman, and also didn't like it - and the gain difference from normally-used 12AY7 is pretty insignificant.

Jim Sliff · From: Lawndale California, USA

A 12AT7 is not usually considered a good "audio" tube; phase inverter, yes, oscillator, sure - but you don't run signal through it. It's a harsh, hard sounding tube (also often thin as Dave mentioned) even though it has lower gain than a 12AX7. Very "edgy" with a nasty-sounding upper-mid hump to the frequency response. That's why Fender NEVER used them in preamp circuits (reverb drivers and phase inverters are not actually "preamp" tubes in a true sense of function).

As posted earlier, a 5751 or 12AY7 can be subbed for a 12AX7 in the preamp (not necessarily when one is used as a phase inverter) and results compared, as those are both audio tubes with a smoother response. A 12AU7 will also work, but often does not have enough gain to drive the signal very well.

A Deluxe is engineered for early breakup - a lower gain preamp tube will help, but depending on how much you want to clean it up, I'd suggest a bias adjustment for sure (it at least needs to be checked), and maybe a speaker change as well.

I did not notice - did you mention what power tubes you are running or if the bias had been checked/set by a tech? That could make a huge difference in headroom.
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No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional

Al Sato · From: Texas Hill Country

I have never liked the sound of a 5751, 12AT7 or 12AU7 (never tried the 12AY7) in V1 or V2 of a Deluxe Reverb. The 5751s I've tried have been very bright-sounding, the 12AT7s sound thin, the 12AU7s sound wimpy to me. However, my Deluxe Reverb has just about all the headroom it could possibly get by using JJ 6V6's and a JBL D120F speaker. I would recommend going that route based on my experience. The JBL made the most difference, so I would start there. It gives the amp a "beefier" sound as well.

Al
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Stephen Gambrell · From: Over there

I put an old RCA 12AT7 in V2 of my Super Reverb, and it sounds just fine---A little bit more clean headroom. Course, I play that amp on "10," anyway...

Jim Sliff · From: Lawndale California, USA

Steve, we talked about that, and you can get lucky with an 12AT7...but that's an unusual success story.

Al, I'd be curious why the 5751's didn't work but a JBL did. I've never found an overly-bright 5751 - which one did you try (I understand the 12AT7 and 12AU7 results - and still suggest a 12AY7 is worth a try)?

If anything, the JBL would be FAR brighter than a 5751 substitution...unless it was a recone of some sort, an impedance mismatch or some other odd situation. It's an inherently VERY bright speaker.

What are your 6V6's biased at?

FWIW another Deluxe mod for increased headroom not mentioned much is subbing 6L6's - you need to know what you're doing, but that's the "Pete Anderson" Deluxe method.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional

Chris LeDrew · From: Canada

Invaluable info, boys. Thanks a million.

Jim, I'd like to hear more about Anderson's power tube solution.......
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Web: www.chrisledrew.com

Al Sato · From: Texas Hill Country

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

I never found a 5751 to be especially "bright". It does have a bit more high-fidelity response, which I suppose might push that upper-midrange and treble honk in the JBL a bit harder.

I also think individual tubes vary, even of the same type, and even of the same brand/type and batch. To me, part of setting up a new tube amp or changing tubes is trying different tubes and just listening, which is why I keep a bunch around. When I isolate a good tube at a reasonable price, I get a bunch of them. I also virtually never throw preamp tubes away - they only rarely wear out and may find useful application somewhere else, even when they don't work, let's say, in the primary gain position V1 or V2 in an old Fender. I just label where they were used, what the issue was, and store 'em away.

Speaker choice definitely affects my choice of tubes, as does what I plan to use the amp for. The whole thing is definitely a complex, interactive system, and each thing can affect the others. I also have a whole different approach to setting up an amp for pedal steel, country, or jazz guitar than for blues or rock guitar.

I think one of the reasons that a lot of people notice differences more than in "the old days" is that a lot of players - especially for blues and rock guitar - push the amps a lot harder than most players used to. My experience is that this is when the differences between tubes, transformers, speakers, and so on express themselves most strongly.

Al Sato · From: Texas Hill Country

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

I mentioned in my earlier post that I seem to recall trying a 12AV7 years ago and didn't like it either. But that is not nearly good enough evidence to make a general conclusion. It could have been a poor variant, a bad example of a good variant, or I might have just been looking for a different sound at the time. I am all for just trying things and letting the ears do the deciding. Of course, at the prices of NOS tubes these days, there are definitely limits. But I do sometimes find them at flea markets, in old electronic equipment, and other places, very reasonably, in which case I generally grab them.

Some of the older American 12AX7 tubes - and interestingly, some of the Chinese 12AX7 tubes distributed by Ruby in the 90s - tend to have a bit of a lower midrange peak, which along with the "kink" in the frequency response of the old-style 6L6 tubes, really give a nice exaagerated-midrange rock and roll sound. Great for some things, but not clean pedal steel, to my tastes anyway. Again, I just try 'em and see what happens.

Jay Ganz · From: Out Behind The Barn

If you want to stick with 12AX7's but want to reduce
the gain, you can always lift one end of the cathode
bypass capacitor. That's the 25uf by 25V cap. That'll
reduce the gain alright. Wink

Jim Sliff · From: Lawndale California, USA

Here's a page that gives quite a bit of information about the 12a*7 variants and similar tubes:

http://www.answers.com/topic/12ax7

I've tried a few 12AV7's and they've worked well - they're just not found as commonly from what I've seen.

I'll also try to dig up the rest of the Pete Anderson Deluxe info for who asked....
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional

Al Sato · From: Texas Hill Country

Jim Sliff · From: Lawndale California, USA

John Dahms · From: Perkasie, Pennsylvania, USA

There is a lot of good info here about preamp tube gain that is good to know but in the case of a Deluxe Reverb their early breakup is more often the 6V6 tubes in the power section. It is safe to run 5881 or 6L6's and rebias the current draw. Frequency response will increase and if biased correctly probably the headroom. A good idea for steel but maybe not so good for lead solos on std guitar.
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Fruit flies like a banana.

Steve Hinson · From: Hendersonville Tn USA

I'd like to find out the particulars on the Pete Anderson mod too...
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