music, guitars & other obsessions

Fender 5F2-A Build

Saw this cheap Fender 5F2-A (Princeton) kit on Taobao, the whole thing was only RMB345, even including the tubes and transformers! It came with a blue chassis, not bad since the amp is known for its bluesy tone. Here is a picture of the chassis (slightly damaged during shipping). Some of the holes were off, you can see the corrections the shop made… I suppose it is good enough for rock and roll?!

The kit has three PCBs – main board, input/tonestack, and effect loop – no PTP wiring here, stuffing the boards were pretty straight forward after I figured out the the kit was really a hybrid design based on the original Fender Princeton and the ProjectG5 modern day version, the main differences were power supply related – the choke was eliminated, and some of the bias resistor/capacitor values were changed. Here are the pictures of the stuffed main and input/tonestack boards. Notice that the pots have different length shafts, I will need to cut two of them shorter…

Here is a picture of the completed kit – under the chassis, it is really not much there since the components were mounted on the PCBs. I don’t like the heater wires running across
the main board but with the input/tonestack board in the way, it did not make much sense to put the heater wires right up against the chassis, oh well…

Here is a shot of the completed kit, it’s pretty plain looking, I plan to make some decals for the faceplate to dress it up a bit, what do you expect for RMB345!
I also changed some of the parts, nothing special – 1)
added two 100 ohm heater resistors to the output cathode pin to provide elevated heater in order to reduce hum (while the ProjectG5 design has the resistors, the kit did not come with them); 2) replaced the silly LED circuit on the input board with a single 6.3V lamp; 3) eliminated the NFB resistor and instead installed a “Fat” switch, which is just a 22uF cathode bypass cap for the 2nd pre-amp stage. 4) I also added a 10 Ohm/10W resistor as a dummy load, to prevent the output from arcing due to an open output, i.e., when no speaker is plugged in.
The sound from the amp is pretty clean, breaking into a mild distortion when volume is all the way up with a small Marshall 6.5″. I am building a “proper cabinet” using an Eminence Raging Cajun 10″ – I bet the combo will be louder and and meaner sounding… So stayed tuned!
Of course, the sound could be improved even more with better tubes, it currently runs with tubes that came with the kit, which are Chinese-made 6N4 and 6P6P. I plan to change them to 12AX7A and EL84 if I can find some cheap ones online.
The build is good for amp builders just starting out, like myself. The 5F2-A’s design could not be simpler – 2 tube-Single End, while the non-original FMA tone stack give it a bit more knobs to fiddle with, really the amp could probably make do with just a simple tone knob like many of the minimalist boutique amps on the market.
Some lessons learned:
1. always double check the connections multiple times, it is simple errors and dumb assumptions that always get you!
2. always use good wires, connectors and the proper tools, otherwise, you either waste time or end up with a crappy looking kit.
Finally, the revised schematic of the build.

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