changing the gain factor with preamp tube.

[chev]

Did somebody ear about swapping the 12ax7 for a 12ay7 to get a lower gain factor and use more of the power tubes without the extreme loudness?

I was told I could do that to be able to open up the power amp section without being to loud. I'm looking to keep the amp as clean as possible with the same level of loudness but with more of the KT-88 warm feel on my 2 Solarus. It has only one 12ax7 so it could make a difference I guess?

here's some cool info from where I get my tubes, you click on the tube you're using and shows with what you can swap it to change the gain factor of the preamp stage.

http://thetubestore.com/gainfactor.html

I'm willing to try that but there's also a notice in the link to check with other users that might have tried it 1st just to make sure.

thanks!

[Isaac]

Doesn't make much sense to me. The power amp section will be driven by whatever signal it is fed. Using a lower gain tube and turning up the volume to get a certain signal strength isn't much different from turning down the volume on your instrument and turning up the volume.

The lower gain tube might have a different tonal characteristic. I suppose that could make a difference.

[EdBass]

The lower gain tube might have a different tonal characteristic. I suppose that could make a difference.

I've experimented with 12AT7's in V1 in some of my amps, for quite a while I gigged a 2000S with a 12AT7 and a quad of Ei KT90's. It did stay cleaner longer (higher on the Volume knob); however, at the sacrifice of a little overall power.
It definitely had different tonal characteristics than just backing off on a 12AX7 in the same amp to the same level, and didn't get any more power tube breakup than the 12AX7; in fact it was less power tube breakup with the 12AT7, but I really don't know how much of the difference can be attributed to the Ei's either.
Like I said, it sounded pretty cool to me, but not so cool that I didn't go back to a 12AX7 and KT88's in that amp. 


It can't hurt to try it out, you may like what it sounds like, but... I'm with Isaac, I'm not at all certain it will accomplish the "cleaner and louder" you are looking to do.

[chev]

thanks for the info!

the guitar tech who told me about it put a 12AY7 on a Ampeg vintage guitar combo, that let him use more of the amp tone without the extreme loud volume.

at least I know it won't hurt anything and it only going to cost me one tube at a time. I even have other gain factor options between 12AX7 and 12AY7 if I find the 12AY7 too low..5751, 12AT7 and might get me a different tone I like more too...?

While I'm there, they sell matched preamp-tube for an extra 5$? those are suppose to have a better balance with 2 matched triodes sections in the tube and works better with phase inverter/splitter circuit...? I'm no expert so I'm wondering if it worth the extra 5$? since I know it's a phase splitter circuit.

[chev]

I've found this interesting guide on what can be done with 12AX7 preamp tubes.

http://www.boiaudioworks.com/12ax7guide.htm

They don't seem to recommend getting a matched preamp tube for guitar amps, I guess it's more for hi-fi amps or the phase splitter tube position.

[Isaac]

Matched preamp tubes seems pointless to me for guitar amps, because the preamp tubes aren't doing the same things in a guitar amp. Makes much more sense in stereo amps, where it's very important to amplify two signals identically.

[chev]

Matched preamp tubes seems pointless to me for guitar amps, because the preamp tubes aren't doing the same things in a guitar amp. Makes much more sense in stereo amps, where it's very important to amplify two signals identically.

cool, that's what I thought.

I'm finally going to get some NOS JAN-Philips 5751 (GF 70), NOS JAN-Philips 12AT7WC (GF 60) and some Electro-Harmonix 12AY7EH (GF 45) to test it out.

I've ear good things about the JAN Philips 5751...so I'll get to ear it myself. 

[chev]

Ok so I've put the EHX 12AY7 to get the lowest gain I could go for a tiny practice room, I finally got to ear what a crank Solarus on KT-88 sounds like...seems less muddy but still insanely loud!

So I back off the volume at 5-6 to get the tone clean before I switch on the Sonic Titan...!

[Isaac]

The thing is, the power amp is always running wide open. Changing the preamp tube doesn't change that, nor does adjusting the volume control. All those do is change the signal that the preamp is sending to the power amp.

[EdBass]

The thing is, the power amp is always running wide open. Changing the preamp tube doesn't change that, nor does adjusting the volume control. All those do is change the signal that the preamp is sending to the power amp.

Yes, but sending less signal to the output stage can drive it less hard, and not saturate as much. I agree that it's not a radical difference between the different V1 tubes being discussed, but I think you can get different tonal flavors from rolling tubes.
However; it isn't always so simple. Amps are designed with certain gain parameters, and just swapping tubes, while IMO generally harmless fun with preamp novals, isn't as cut and dry as some may think.
To properly utilize a different tube(s), the entire circuit needs to be optimized for those characteristics.
IMO unless you are prepared/capable to take those measures, generally an amp will perform best  when using the tubes that the designer designed the circuit around. From input to output an amp is (hopefully) designed to work in synergy, with all of its parts playing their role, and it’s a delicate balance to actually get it “right”.

Different tubes have different tonal qualities for sure, but if you want cleaner, back off the volume control. There isn’t a magic “plug in” fix, and just by rolling much lower gain tubes through V1 you can actually get things real sludgy.
I think anything lower gain than a 12AT7 is really pushing the design envelope, as I mentioned before my AT7 experiment ended up with me swapping back to the proper tubes.

[Ryanx]

i religiously used a 12at7 in my model t.  i felt it tightened up the sound i was getting.  when i would run a 12ax7 in it, it seemed to lose a lot of flavor and be really fuzzy/muddy.  when i would run a 12at7 it seemed as if it cleaned up a lot of that noise when i was in my higher volumes.  i then got wise and traded for a 1200s.  Haven't looked back.   

[chev]

cool, I've been using the EHX 12AY7 all wkd and the sounds is much more smoother, less fizzy highs at high volume...so for now it will do.

[Isaac]

"Yes, but sending less signal to the output stage can drive it less hard, and not saturate as much."

Of course, but turning down the volume control will send less signal to the output stage. So will turning down the instrument volume.

I think the goal here is to drive the output stage to saturation, or near to it, while not distorting the earlier stages. That may be possible or not, depending on the amp's design, and I don't know if it's possible with chev's amp. But a high gain tube with a large input voltage could be clipping on peaks in the first stage, before the volume control. A lower gain preamp tube could prevent that but, as you say, may not be a good fit for the amp design.

[chev]

"Yes, but sending less signal to the output stage can drive it less hard, and not saturate as much."

Of course, but turning down the volume control will send less signal to the output stage. So will turning down the instrument volume.

I think the goal here is to drive the output stage to saturation, or near to it, while not distorting the earlier stages. That may be possible or not, depending on the amp's design, and I don't know if it's possible with chev's amp. But a high gain tube with a large input voltage could be clipping on peaks in the first stage, before the volume control. A lower gain preamp tube could prevent that but, as you say, may not be a good fit for the amp design.

sounds right!

the design has only 2 tube in the preamp stage (usually a 12AX7 for preamp gain and a 12AU7 apparently a reverb driver) so no drive stage there, just clean.

So I'm guessing the dirt pedal might be like adding a second preamp gain tube in front of the 12AX7 section, it will saturate the signal enough before the 12AX7 section so I want to make sure there's no more gain saturation added there.

Now I get my 2 main dirt tones tight and focus with the 12AY7 with a usable volume, I could try going back up closer to the 12AX7 and see if it stays that way...?

But the dirt pedals gives a significant volume boost and I don't really use the clean except for testing, if it's clean at a good level, then I know the dirt is all controlled from the pedal.