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Discussion in 'Amp Tech Center' started by TheHoneyMonster, Jan 4, 2014.
what is the best 12AX7 replacement to get more clean hedroom out of an amp???
You'll get varying answers, I would start with a 5751. However, it really depends on where the distortion is occurring. If you are getting preamp distortion, changing the tubes might help. If you are truly running out of headroom and you don't have room in the power amp the answer isn't tubes it is adding more speakers or more efficient speakers.
+ 1 on the 5751
not sure about the new stuff being labeled 5751, but a good old RCA 5751 is hard to beat !
Really depends on what your putting it in !
My 59 Bassman LTD does indeed have a 12AY7 in V-1 just like the original did.
yes its the preamp, i can get a good clean sound but the moment i ad med gain, the preamp just cant handle it, and over compresses everything
I started with the stock Sovtek 12ax7 tube.
Went to a NOS GE 5751 tube.
Until I finally found 'the sweet spot', with a NOS Sylvania 12ay7.
Clean headroom is usually determined by the output stage. Not the preamp tubes.
You can swap tubes till hell freezes over in something like a Princeton and not gain much clean headroom.
Replacing a trio of 12AX7s with lower gain 12AY7s, you will be able to turn the amp up much higher on the dials, but you will still be making the same power output when the tubes hit saturation. Changing transformers are basically the only way to increase power output in any significant quantity to obtain meaningful increase in 'headroom'.
Upgrading to a more efficient speaker is a much more effective way to increase volume, but there's a limit, and if you've already got a 100dB-ish unit installed, there's not much farther you can go.
Headroom relies on a lot of factors, but generally, the 12AY7 makes many amps more useable at lower volume levels without dirtying up.
+1 5751, I am also using an old Westinghouse 12AU7 in V1 of my Pico Valve that is pretty killer.
The amount of gain decreases with each but exactly how much clean headroom you add without a significant loss in volume is gonna vary depending of the amp. Basically is goes like this.
Tube = gain factor
12AX7 = 100
5751 = 70
12AT7 = 60
12AY7 = 45
12AV7 = 41
12AU7 = 19
I've run a 12AX7, a 12AT7, and a 12AY7 in my 5w Bugera Class A. That's very simple amp and for me the 12AT7 was the best balance between clean headroom and volume. YMMV depending on how your amp responds to the changes. I couldn't really judge which worked best until I has experimented a bit.
Among new production tubes I have liked the ehx 12ay7 and got 2 jj 5751 that were unusable due to microphonics. I agree that this won't improve your clean headroom in terms of absolute volume but will give you a couple more clean numbers on the volume knob.
A lesser gain preamp tube will help a lot. I just pretty much use any of the 12a_7 famly that isn't the 12ax7. The ay7, au7, what ever I have laying around.
What specific amp are we talking about?
A Laney Cub 12R
How much clean headroom are you looking for ? It's a 15 watt amp that maybe the problem.
i know that a 15 watter isnt going to have much, but its still breaking up with the gain on 1-2
Take a look at some of the Eminence speakers, the Redcoat series (British sounding) are
almost all built around 101dB-103dB of sensitivity !!
may do that phil, but it still seems that its the preamp thats the spanner in the works