Fat Prince

A 22W, single-ended, Class-A combo guitar amplifier with 12" Celestion speaker.

( Originally had this set up to deliver 30W (hence any notations to that effect on the vid), but decided that was just too close to the max, and considering the cost of KT-120s, decided to favor longevity!)

 

Fat Prince is a 22W, single-ended, Class-A combo guitar amplifier with 12" Celestion speaker.

The impetus for this design was a desire to take the features that make the early Fender tweed Champ such a desirable recording amp but scale it up to at least the power of a Fender Deluxe (~22W).

The original prototype achieved this goal using a single KT88 power tube, but in the interim, Tung Sol introduced the mighty KT-120, which allowed me to get more clean headroom, always difficult with lower-wattage amps.

It's built in an off-the-shelf Tweed Princeton chassis, and hence the name.

My plan is that if I decide to build a further refinement of the design (possibly with a single KT-150 (~30W) or a pair of parallel KT120s (50W), or a pair of KT88s in push-pull (45W in Class A, 100W in class A-B), I'll be able to use a relatively inexpensive and compact off-the-shelf cabinet.

This cabinet is solid pine with solid maple framing. Covering is 24-Oz hammock canvas (approximately twice the weight of the original tweed covering fabric), finished with shellac and spar varnish.  Corners are NOS units from an old steamer trunk restoration supplier.  Leather handle is from the same source.

I could actually build this design with just two tubes: a twin triode (i.e., 12AX7), and a power tube, but I chose to use an octal-base (current production) 6SL7GT twin triode with both sections in parallel, for more clean headroom, and an EF86 small-signal pentode for tonal complexity.

Controls consist of on-off, volume, tone (pull to bypass for volume boost), and a 'penalty-free' Master Volume, which replaces the essential grid load resistor in the power section so as to avoid any unnecessary signal loss when turned all the way up.  The control is bypassed by a 4000pF capacitor that serves to prevent muddyness when the MV is turned down.  (At full volume it is completely bypassed.)

 

 

 

 

(click to enlarge)

Not for Sale