Fender Champ clone with improvements

[j4zz]

I actually built this little amp a while back, but with my increasing interest in playing jazz in recent years, I have just fetched it out of storage and placed it in my computer room for practice and playing along with tracks from the computer. It is based on the same 12AX7 & 6V6 circuit all the champs used, but I decided to add a full 3-way bass/mid/treble tone stack.


Another thing I changed, in the hope of improving the clean sound, is to replace the volume control with a separate gain, and master volume setup, so each 12AX7 stage drive can be controlled. That combined with a multi-effect pedal in front, gives me heaps of control. The pedal also provides reverb/delay/tremelo etc etc of course. Also, for a cleaner sound, I used a solid state rectifier circuit in the power supply.


So, as long as I don't crank it, I find I can dial in quite a nice jazz sound. I think it is mainly the 8" speaker that keeps it from staying clean when I push it hard. The speaker is an old speaker from a wrecked practice amp I bought for parts. I think I should upgrade the speaker sometime. I built the Fender Champ clone into the same box and chassis that the speaker came from.

I mostly use it with an archtop that has a floating humbucker pickup. Really liking it.

[Sigmund451]

I wish I had those skills but Im clueless with electronics. Id step up to a nice cab and a good 10 inch speaker. All that work deserves a nice presentation and a good speaker. If you have some basic tools and some time a cabinet is not that hard to build. This is one I built for a 12 inch speaker. Its glued and screwed. Mine is heavy becusae I had old oak shelves and I wasnt going to carry it anywhere. I used a cheapo table saw, a drill, screw gun and a couple of clamps. It was a whole lot easier than what you have done so far.

[darkwaters]

Replace the 12ax7 with a 12ay7 and you should find that you have more headroom and a bit more travel on the volume knob before distortion begins.

[j4zz]

Replace the 12ax7 with a 12ay7 and you should find that you have more headroom and a bit more travel on the volume knob before distortion begins.

Yes, there are a whole series of types in the 12a*7 series with different gains. 12AT7 was common as well, as of course the low gain 12AU7. There are others as well. Worth an experiment but I expect just changing the gain might just result in the controls sitting in a different position, but everything sounding similar.

Definitely will try it anyway.

[j4zz]

A handy chart Preamp Tube Gain Factors And Substitution Chart – 300Guitars.com

[darkwaters]

Yes, there are a whole series of types in the 12a*7 series with different gains. 12AT7 was common as well, as of course the low gain 12AU7. There are others as well. Worth an experiment but I expect just changing the gain might just result in the controls sitting in a different position, but everything sounding similar.

Definitely will try it anyway.

I’ve found a 12au7 makes an amp just too wimpy and 12at7s aren’t meant to be a preamp tube and if you try one you’ll quickly understand why. They just sound horrible.

For some small amps a 12ay7 is just the ticket IMO. I currently have 2 Champ style amps; one benefits from the extra oomph of a 12ax7 (actually a low noise 7025), the other is a raging beast that needs the bit of taming that a 12ay7 provides.

[j4zz]

12AT7s have been used as general purpose gain stages (preamps) in many pieces of equipment. Not so common in guitar amps, for sure, as they have only mid-level gain, but sometimes that is enough.


In other areas, I have just ordered a Jensen 8" speaker for it. Mostly I hope in cleans up the bass, which is currently a tad heavy in every tone control position bar minimum, and muddy. Reviews say the C8R has tight bass.

C8R | Jensen Loudspeakers

[stevo58]

For mid-level gain I like the 5751. I bought a boatload of GE 5751 back when they were about $20/each. They last forever. I often like the 12ay7 too, or its milspec version. The 12au7 has always been too wimpy when I tried it.

The 12at7 is designed as a driver tube, a current amplifier, rather than a voltage amplifier. This is why they are often used as the reverb driver or the phase inverter. Doesn’t hurt to pop one in and try it. I was going to say they are cheap, but my knowledge of the tube market is outdated; I haven’t had to buy anything for ten years as I laid in enough stuff to last me to the end of days back then.

Regarding the Champ: the tone stack sucks a lot of gain; did you compensate by bypassing the cathode resistor or make other adjustments? I’m assuming a 5F1 here rather than a BF.

[j4zz]

For mid-level gain I like the 5751. I bought a boatload of GE 5751 back when they were about $20/each. They last forever. I often like the 12ay7 too, or its milspec version. The 12au7 has always been too wimpy when I tried it.

The 12at7 is designed as a driver tube, a current amplifier, rather than a voltage amplifier. This is why they are often used as the reverb driver or the phase inverter. Doesn’t hurt to pop one in and try it. I was going to say they are cheap, but my knowledge of the tube market is outdated; I haven’t had to buy anything for ten years as I laid in enough stuff to last me to the end of days back then.

Regarding the Champ: the tone stack sucks a lot of gain; did you compensate by bypassing the cathode resistor or make other adjustments? I’m assuming a 5F1 here rather than a BF.

Yes, cathode resistors are bypassed, except for the feedback bit. I have plenty of gain, as I always intended to use a pedal to add reverb, and that can have gain configured as well.

I think, from memory, I started with the AA764 circuit, not the old 5F1, and substituted the three way tone stack instead of the two way. Also like the vibrochamp (without the vibro bits).

edit: oh and I have plenty of 12A*7, good pulls, sitting in boxes, so they are all cheap at this point.

[stevo58]

I think, from memory, I started with the AA764 circuit, not the old 5F1, and substituted the three way tone stack instead of the two way. Also like the vibrochamp (without the vibro bits).

Of all the amps I built, my favorite is a vibro champ that I spliced in the Fender reverb circuit. I’m running it with 2x8” but I built a couple for other people with an 8”/12” combination. Significantly larger cab though. When I played in blues bands I would turn it up to 80% or so and control the volume on the guitar, most of the time working around 3-4 on the guitar. The Champ is more versatile than people give it credit.

[j4zz]

Of all the amps I built, my favorite is a vibro champ that I spliced in the Fender reverb circuit. I’m running it with 2x8” but I built a couple for other people with an 8”/12” combination. Significantly larger cab though. When I played in blues bands I would turn it up to 80% or so and control the volume on the guitar, most of the time working around 3-4 on the guitar. The Champ is more versatile than people give it credit.

I thought about building a reverb into the amp, but decided these multi-function pedals are just too easy to use in front of the amp.

I am expecting the new Jensen speaker to be louder than the existing one, as it was from a SS guitar amp, and so, most likely not very efficient. I won't be gigging with this one (unless I fall in love with the sound and just decide to stick a mic in front of it on stage )