This latest creation is the result of a "happy accident." A customer hired me to convert a 3 channel 1950s-60s tube driven PA head to a guitar amp.
Using the original transformers and tubes (three 6EU7s & a pair of grid biased pair of 6L6s), I converted the preamp to a modified 2203 Marshall preamp and altered the output section to a common cathode bias as well as eliminated the negative feedback loop, all in the original chassis.
FEATURES: The features include a volume or gain control, a tone stack and a post phase inverter master volume control.
Also included is the second design of my "Wave" control results in making the output signal asymmetrical, by adding as well as subtracting signal amplitude to one output tube while the signal remains consistent to the other output tube. This also results in an adjustment of the amp's signal harmonics.
Instead of waiting for another one of these chassis to appear on eBay and instead of using three 6EU7s I cloned the modified PA amp head by using Hammond transformers with similar specs and three 12AX7 (which have the same amount of gain but are more commonly available than 6EU7s), used the generic Princeton chassis to add to a combo cabinet.
Another alteration includes using silicon rectifiers instead of a rectifier tube which is used in the original chassis in which a 5AR4 is used. The amp is only 20 Watts RMS but is amazingly loud especially if connected to a 4X12 speaker cab.
A friend of the owner of the first conversion amp has been buying every PA head of that same brand that he could get his hands on, and commissioned me to build one for him, a backup model along with two more to do for the first owner, one for the other guitar player in his band and one for a friend who owns a recording studio.
CHOICE OF CIRCUIT:
Preamp with or without Cathode Follower
Any version of Phase Inverter
Grid biased or Cathode biased Push-Pull Output Stage or Single Ended
Master Volume or none
Tone stack with or without bypass
Tone control or none or with Tone Stack and/or Tone Stack Bypass
Wave control (controls harmonics)
Warp control (warps the signal like a distortion pedal)
Reverb with or without additional Dwell control
Tremolo (Depth and Speed controls)
Volume control is obviously required but still optional if one prefers to control volume with their instrument
CHOICE OF COMPONENTS:
Preamp Tube Choice: Newly manufactured by former Soviet Union countries, etc.
Power Tube Choice : American made NOS tubes made for Television functions but can be used as amplifier tubes (strongly recommended since they are American made therefore last 10 times longer than contemporary tubes and cost less. Plenty available).
Resistor components: Carbon composition, Carbon film, Metal film, Wirewound
Capacitor components: Polyester, NOS paper & oil, Newly manufactured paper & oil
Transformers: These have to be selected based on one's tube & speaker choice.
Rectifiers: Recommended are Solid State diodes, but if one insists on a tube rectifier they need to shell out an arm and a leg for a NOS Mullard or American made rectifier. The contemporarily manufactured tube rectifiers are simply not that reliable and can do some serious damage to your amp when they fail. Either go NOS or with solid state diodes. Sag can still be simulated if so desired.
Note: There may be limitations on certain feature combinations depending on the choice of combination.