A hybrid design based on Ken Fischer’s Express circuit. This amp is a very loud and aggressive amp that can peel paint off the walls and make ears bleed… when that sort of thing is needed.
This is a very modern take on a classic tube amp design. For this build I had custom printed circuit boards made and also used a lot of current production electronics. A really fun amp to play and guarantees that you will not go un-noticed.
Printed Circuit Boards are generally considered taboo in the world of DIY tube amps. This is largely due to the fact that they are used as a fabrication short cut to simplify the production time required. In this build they allow some strategic technical options that serves tube amp construction very well.
Typically, all the metal used to fabricate and populate a circuit board is working against you as it acts like an antenna that collects random electrical noise… basically acting like an antenna. Printed circuit boards use a minimum of metal by replacing the “turrets” and wire leads with flat thin traces of metal. An additional bonus is the circuit paths are fixed so the wiring placement is never or moving in and out of locations where “cross talk” can cause electrical noise issues. Finally, having traces on the bottom and the top of the boards allows for all power and signal wires to cross each other at exactly 90 degrees, providing the most ideal wiring layout for tube amp fabrication.
The end result in this build is simple, tidy, and quiet. I did some early testing with a pair of 6V6 output tubes but ultimately I selected a nice set of old European EL-34 output tubes. I sorted through a bunch of preamp tubes and found some that sounded right and didn’t have any excess noise. I used original spec Wreck transformers from Pacific and vintage CDE/Mallory couple caps inside the chassis. The layout is the same as an original Express build with the exception of the filter caps in the power supply.
Note the simplicity that the power supply filter “can caps” add to the design of this amps. These JJ cancaps are modern production and allow for very easy maintenance when it’s time to replace them. The chassis is made from .090 thick 5052 aluminum and was powder coated in white.
Every amp I build allows something to be learned… note the secondary impedance switching option on the output transformer and a rear panel label. Since then this amp has stayed buttoned up and remains ready to gig when the opportunity to play incredibly loud comes around… which you can tell is rare by the well preserved TOLEX covering.