As a purest, I never could find an overdrive pedal that I liked. Long ago I set out on a journey to get the best possible rock amp with no diode clipping, just pure vacuum tube sonics.

I’ve always loved the 6G16 Vibroverb circuit, and have built several, each time trying something new and making progress towards turning that circuit into something better. Significant adjustments have been made to the power supply and tone stack, and significant achievement in its tonal palate and response.

This is Vibroverb #3.

It has been designed to have a great edge of breakup tone at moderate volumes, and heavier rock tones at higher volumes. The classic fender cleans can be found at lower volumes, but mostly was designed for its edge of breakup tone, and its rock tone.

It’s midrange has been boosted and it’s output lowered. It puts out around 30 watts.

All components were hand selected from my NOS parts stash.

Transformers- The power transformer is what makes the sonics possible, to get where I wanted to go, I needed the right voltages and current handling.

NOTE: The power transformer WILL handle any pair of output tubes you throw at it, no need to worry about the heaters.

6550 or KT66 or EL37 or 350B is possible.

I wired the output sockets blackface style, so you cannot put EL34 in it without modification, although the PT will handle the heater current draw of the EL34 as well.

I’ve tried many new production and NOS output transformers over the years from magnetic components inc, Mercury magnetic, Stancor, Triad, Merit, Thordarson etc.

While some of those sound good, and others just ok, none of them can deliver what an old Schumacher from a fender amp can. Many AB comparisons were performed with the assistance of a great friend of mine and both our ears agreed, if I was going for an incredible tone, I needed an early Schumacher. This one is from the 15th week of 1968

Capacitors-

The coupling caps chosen are vintage Cornell Dubilier PM caps. They are Mylar caps just the same as the blue molded caps found in old fenders and they were made around the same time as the blue molded caps.

The blue caps in old blackface amps are rarely found to be leaky or bad after 60 years in service, so I knew the green PM Mylar caps would be an excellent choice, and since my stash is nos, they may well last 60+ years in my builds as well.

In addition to all that, Ampeg used the same coupling caps in the B-15 bass amps.

If Mylar was good enough for Leo Fender, then they are good enough for me, ditto the carbon comp resistors.

And if the green pm caps were good enough for Ampeg, they are good enough for me.

This amplifier has had its cathode bypass caps reformed prior to the build, from my NOS stash of Cornell Dubilier capacitors, and it’s power supply electrolytics are new Jensen capacitors.

Tonal palate of the #3 is between clean, edge of breakup and classic rock depending on where you are on the volume control.

Two Notes on the tonal palate

#1- it reaches edge of breakup at about 3 1/2 to 4 on the volume control which is much sooner than a blackface fender.

#2- The Headroom can be tailored with the rectifier tube or Weber copper cap.

I recommend a 5V4GA for most breakup, a GZ34 for in the middle, or a Weber copper cap for most headroom.

I am offering this as a chassis only! You will need a head cabinet , and a reverb tank.

Note: the vibroverb and super reverb have the same chassis size, so any head cabinet or combo cab that is for a Super Reverb or Vibroverb will work for either.

4 ohm load, 30 watts

Tubes-

RCA 5V4G rectifier

RCA 6L6GC

RCA 7025 and 12ax7a throughout.

You may use a solid state rectifier or GZ34 to increase headroom for more available clean tones on the volume control.

The #3 is outfitted with cut control between the output tubes, this is used to set the top end treble to your own desired spot, whatever your ears like.

The #3 has been moderately adjusted from the 6G16 schematic. It’s tone stack is somewhat AB763 with a slight twist to my liking and boosted mids.

There are a few blemishes on the face plate, nothing serious. Please see left of the pilot light the white dot, that’s a boo-boo.

This is NOT a blackface fender sound, it is significantly better than that.

Ive built and sold many amplifiers over the last 15 years.

Im down to my favorite 4. Which are all variations of this amplifier, i will list the others this coming week some time.

Each has its own character and sound, but all are loosely based on the achievements of the 6G16. I have optimized the circuit for the modern players.

Please ask any questions you may have.