XXX re-tube

I'm planning on having my peavey triple XXX head retubed soon and plan on switching from the 6L6 power tubes to some EL34 power tubes (it has a switch that allowes this) I'm also going to change the pre-amp tubes and want to put some 12AX7's that arent as high gain. Any suggestion on what brand tubes to go with. Also this head has some kind of built in nois suppressor/gate or something that I find can be annoying when trying to use my guitars volume knob to roll back on the distortion. Is there any way to get rid of this or bypass it. Also the transformers(?) are geared for extreme gain so neither of the dist. channels clean up much when rolling back the guitar's volume knob. Is there anything that can be done about this too? Am I waisting my time with all of this? Should I just go ahead and get a different head? The XXX is a really good sounding amp for clean and very heavy, but nothing in between. I actually never have the gain turned up past 10 o'clock on either one of the dist. channels. I'm finding that less is more in the distortion department. I think I might just sell the head and get a Marshall DSL100 or something of the like and be done with it. Any idea's or opinions on any of this?

12AX7's all have the same gain (amplification factor) of 100, plus/minus about 5%. 'Golden Ears' types will tell you different, but the measuring equipment tells no lies. There are several other tubes that you can try without making any mods to your amp. The beautiful thing about preamp tubes is that you don't need to rebias anything. Just make sure that the pins connect to the same internal parts of the tube.

You can try 5751's which have a gain of about 70. This gives you a bit more headroom before distorting, and they are reputed to sound good when they do distort. SRV used them.

The 12AT7 has a gain of about 60. The 12AY7 has a gain of about 44.

With a gain of about 20 is the 12AU7 which is easy to find. Ampeg used them for some of their amps, usually as the driver for the power stage.

All of these tubes will simply plug into the socket the 12AX7 was in - no fuss. Just try 'em out and shuffle tubes around until you find a combination that suits your tastes.

I find this site usually has data sheets for tubes I want to check out. Compare the size and pin connections with the 12AX7 data.

one more, well, two more questions. the amp uses 3 pre-amp tubes. when changing to a different tube, do you have to use the same type in all three positions, or could you use a different one for each position. Also since the amp is a 3 channel amp and uses 3 pre-amp tubes, does that mean that each channel has it's own pre-amp tube? that might be a stupid question, but hey, you never know if you don't ask. Thanks for the info.

'Can't be sure without a schematic. Each tube has two sections in it, so each one could be a separate two-stage channel. If each channel has it's own EQ or Tone controls, this is probably what's happening.

The whole idea here is try something different. All three channels are using 12AX7's, so you should swap out one of them to see which channel that tube controls, and to see if you like the new tube better than the original. You might also want to try a 12DW7. This has one high-gain (100) section like a 12AX7, and one medium-gain stage like a 12AT7.

Look at the base of a tube, and you will see that there is a gap where it looks like a pin is missing. This feature allows you to be sure to get the right pin in the right part of the socket. Shut down the amp, and use a clean, dry cloth to grip the tube you want to change. [u]Gently[/u] rock it back and forth a little bit as you pull it out. Note which way the gap in the pins is facing, so it will be easier to line up the new tube with the socket. Install the new tube, again rocking it gently as you push it all the way into the socket. Now, fire up the amp and see if you like it.

[Edited by Lordathestrings on 02-13-2004 at 12:35 PM]

each channel has it's own eq. the 2 dist. channel's have active eq controls while the clean channel has passive eq controls. changing the pre amp tubes sounds easy enough, but what about the power tubes. how do I make sure they're biased right? right next to the power tubes is a switch to specify 6L6's or EL34's and next to it is a bias knob. Would I need a special instrument to check the mv of the bias(or whatever it is), or could it be done by sight and sound? Do power amp tubes have a gain rating like pre amp tubes, or are they pretty much all the same possibly varying somewhat between different manufacturers. What would be a bood brand to go with. Sorry to ask all the question, but I want to learn as much as I can. While we're at it, what is the link to that tube web sight you so often refer to? Would I be able to find some of the answere's to my questions there.

Setting the bias correctly is something of a 'Dark Art', in that the numbers in the tube data sheets don't necessarily give the best results. I take my amps to the local amp guru, and I recommend you find a good tech in your area.

One of my favourite amp info resources is Amptone.com. Some of the discussions on there are pretty old, but hey, we're dealing with a technology that goes back about 100 years! :)