Mojotone Princeton Reverb Clone Project

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The amp kit was shipped in three boxes. The first two boxes contained everything except the wood cabinet. The cabinet itself arrived a couple of weeks later (the exact timing depends on what is going on in the Mojotone woodshop).

Photos of all parts

Parts list

Resistors (mostly carbon comp, default power rating is 1/2 Watt)

VALUE (ohms)  COUNT   NOTE
47                1   bottom of mixer (to ground)
100               2   6.3V loop (since not center tapped)
1K                1   cathode of driver
1K-2W             1   power at output (metal oxide)
1.5K              4   cathode 12AX7
2.2K              1   cathode 12AT7
2.7K              1   negative feedback loop
6.8K              1   to ground of tone
22K               1   bias circuit
3.3K              1   trem cathode
15K-2W            2   power on mixer & driver (metal oxide)
56K               2   phase split on driver
68K               2   input circuits
100K              7   3 input (plate/tone), 1 plate mixer, plate reverb ret, 
                      next to diode, near speed pot on trem
220K              4   2 input of 6V6s, reverb ret input, plate of trem
470K              1   reverb return
1M                6   3 in trem, 1 input, grid on driver, grid on 12AT7/reverb
3.3M              1   between tone/mixer on reverb pullout

Caps

VALUE               TYPE      COUNT  NOTE
100uF@100V          AL/elect      1  by diode
40/20/20/20uF@500V  can           1  power supply
25uF@50V            sprague atom  6  cathode: reverb(3), trem(1), in(2),mix
0.1uF@600V          orange        4  tone, driver out(2), trem output
0.047uF@600V        orange        2  bottom of tone, death cap
0.022uf@600V        orange        3  tone out, mix out, trem out-ish
0.02uF@500V         disc          1  (20nF) trem
0.01uF@500V         disc          2  (10nF) trem(2)
0.0033uF@600V       orange        1  (3.3nF) reverb return
500pF@500V          silver mica   1  reverb in
250pF@500V          silver mica   1  treble tone
10pF@500V           disc          1  reverb in/ret

diode

TYPE   CNT  NOTE
1N4007   1  rectifier diode for 6V6 bias supply, 1A 1000V

screws/nuts

TYPE             COUNT  NOTE
screw 4-40 1/4"      8
screw 4-40 3/8"      6
keps nut 4-40       14

screw 6-32 1/2"      6  pan head, phillips drive, zinc machine screw
keps nuts 6-32       6  for copper head baffle screws

screw 8-32 3/8"      6  pan head black oxide
keps nuts 8-32      10  for speaker screws and chassis straps

screw 10-32 3/4"     8  
keps nuts 10-32      8  for tweed chassis screws

total provided screws: (8 + 6) + 6 + 6 + 8 = 34
total provided nuts:   14 + 6 + 10 + 8 = 38

The above does not include the chassis mounting straps screws/nuts, the truss head screw that goes with the white cable clamp, the screws used with the 1/4 inch speaker jack, or screws/nuts that are pre-installed in the cabinet. Note that the kit appears to include more screws and nuts than needed to build the amp, so you have to puzzle out which ones to use where. Some data to help:

sizes are specified in [diameter]-[threads-per-inch] [screw-length]
the 4 additional 8-32 nuts are for the power transformer
4-xx is the biggest screw that fits the chassis tube holder holes
8-xx is the biggest screw that fits the reverb transformer
6-xx is the biggest screw thar fits the cap can clamp
we need 25 screws and 29 nuts:
- power transformer mount: 4 (nuts only)
- 8 pin tube holders (2 per holder): 6
- 9 pin tube holders (2 per holder): 8
- reverb transformer: 2
- cap can clamp: 2
- output transformer: 2
- rectifier diode eyelet board mount: 2
- main eyelet board mount: 3

Misc parts

NAME                            COUNT   NOTE
white power cable clamp             1
truss head screw                    1   black cabinet corner screws
grommet for 3/8" holes              6   (3 more than needed?)
RCA phono jacks                     4
#47 pilot light bulb                1
light lens (red)                    1
pilot light assembly                1
chassis straps/screw/nut 4 5/8"     1
3M pot                              1   speed
1M-A pot (vol/tone)                 1   volume
250K-A pot                          2   treb/bass tone
250K-L intensity                    1   intensity
100K-L pot reverb-lvl               1   reverb level
knobs                               6
1-9/16" (40mm) mounting clamp       1
18/3 power cord strain rel.         1
18/3 power cord 6'                  1
3 lug terminal strip                2   you decide where to use them
fuse holder                         1
1A slow blow fuse                   1
swcraft J11 out/ext 1/4"jack        1
switch J12A 1/4" shorting jack      3
eylet rect board+backing            1
eylet PR board+backing              1
9-pin tube sockets shield base      4
9-pin shields                       4
8-pin tubs socket                   3
tube clip for octal base tube       3
SPDT ground toggle switch           1
SPST power/stand switch             1
green 18Ga solid wire             10'   heater hookup wire
black 18Ga stranded                3'   speaker wire
white 18Ga stranded                3'   speaker wire
white 22Ga solid                  25'   main hookup wire

Note that if you want to install a 3 lug terminal strip on a power transformer screw, you may have to split apart the strip's loop to get it to fit around the screw.

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This page maintained by Chuck Cranor