I have an unmodded circiut V18. I have replaced the reverb pan with a new accutronics which is the only mod I’ve made. I’ve swapped a few tubes around but its back to stock now. I just got my hands on a set of real nice vintage RCA 12AX7A’s that I pulled from an old Lowrey organ. The tubes are marked 61-22 274. My question is has anyone tried replacing the stock tubes with vintage RCA’s without doing any other mods? I am curious as to what difference you got with just the tube swap. I’m going to try the swap myself, but I won’t be able to get to it for a couple days so I figured I’d ask and see what others know.

While I’m at it I’m also going to try an old Sound City By Sylvania 12AU7 that is marked H6V 713 and an old RCA 12AT7 that I can’t read any markings on other than Made in USA.

To compare them I’m going to first record the amp with stock tubes. The I’ll swap out something, and record again with the same guitar, same settings on the amp, etc. This way I’ll get an idea of how it sounds while I am playing, plus I can refer back to recordings to compare.

From the tubes I’ve mentioned, which would be your first choices to try? Of course I know the first things you’ll all ask is what kind of sound am I looking for. I play blues, rock and some metal (when I feel like letting out some frustration ) I play mostly at low volume and I like anything from a sweet clean to heavy OD/distortion. I do have pedals I use at times for low volume playing, a Bad Monkey and a Marshall Guv’nor.

I do have the speaker broken in pretty good and it sounds much better now. Also because of the volumes I play at I don’t really have issues with overwhelming bass or boxy tones. I can dial in pretty good tone with it stock at the volumes I play. Of course pretty good means there is room for improvment. I’m staying away from circiut mods for right now so I don’t void the warrenty so soon. I guess if I was playing at louder volumes more mods might be needed, but at the volume I play I can easily get all the clean I want.

If you thought a you could crank a 5 watt tube amp late at night in your apartment, you’d be dead wrong. Even through a small speaker it would be as loud as someone screaming at the top of their lungs. Most amp manufactors don’t realize that there is a large demand for very low watt tube amps. Lets face it, we love that fully cranked tube amp tone, but how do we get it at a volume you can play in an apartment?

As the owner of three 5 watt tube amps I can tell you from experience they can shake the walls when you crank them up. Even 1 watt going into a good quality speaker fully cranked would easily be loud enough to piss off the neighbors. Many musicians use small amps like fender champs in the recording studio. This way they can crank them up and get really great tube tone at a volume that won’t make their ears bleed.

Whats really great is when you hook up one of these little 5 watt beasts to a larger speaker cabinet like a 4 x 12, they roar! I have one of mine, an old silvertone tube amp that I pulled from an organ are rebuilt for guitar and its driving a 15" eminance speaker, I get some really bluesy tones out of it, I love it! Its a beast with the 15", with the 5 watt tube amp cranked it shakes walls and windows. The tone is incredible, very full and you’d be suprised at how well it handles both the hgh end and the bass. it can get very bright or thunder and growl, all with the flick of a pick.

I started the basic work. So far I’ve removed the power switch from the vibrato control and have it wired to a 250v 3 amp toggle switch that I have mounted in the old preamp chassis. I’ve also got two input jacks mounted in the chassis that re already wired on the jack end. I clipped the  wires going to the vibrato control pot and labled it with masking tape so I’ll know what it was when I wire in the new pot for the vibrato.

I’m going to disconnect the top and wiper of the "Swell Pedal" pot. and give the 6AQ5 grid a new 1Meg resistor  to ground, and the existing C5 0.01u cap from V2B. The I will disconnect the end of C4 which goes to 1meg R11 and V2B grid. C4 now feeds top of "Swell" pot. Pot wiper goes to V2B grid. Once this is done it will be a standard volume control. I’ll then disconnect "Flute/String" switch and install a standard guitar input jack(s) with a new 68K and 1Meg resistor.  This will be about 95% of a second version 12AX7 Champ with a  tremolo. The 2cnd Champ is VERY clean until the power tube in cranked hard.

I just replaced the 15k NFB with a 1.5k and I’m getting a little overdrive at full volume. Its not as loud as my vibro champ and it would be cool to be able to get some more gain. I am thinking about trying another 1.5k in parralell with the first one to see if I get more gain but I’ll wait until someone here lets me know if its safe.

I would like to keep the nice clean tones but would also like to get more overdrive when I want it. This might be a good use for the extra 12ax7, maybe I can add a switchable gain control with it. I really like the tone I’m getting from the 15". But as I mentioned before its so clean even at full volume which is about half the volume of my vibro champ, not that I mind it being quieter, but It sure will be nice to get some overdrive going on this. It does sound great with a bass too which is cool since I don’t have a bass amp right now. I’m hoping to get this to the point where it I can use it for both guitar and bass.

Here is a pic with the chassis just sitting on the bottom, plenty of room on all sides and an inch or two of clearance between the speaker and the  tubes depending on exactly where I decide to mount it.