First Part - Marshall 1960B 4x12" cabinet modified with X-pattern speakers combination

Among all the extension cabinets of famous amplifications, Marshall 1960 Lead cabinet is the standard of this industry.
This cabinet is equipped four Celestion classic G12T-75 speakers (16 ohm, 75w).

My modification followed Bogner famous Uberschall 4x12" cabinet (a.k.a "Uberkab").
Bogner Uberschall 4x12" cabinet is loaded with each pair of Celestion G12-T75 speakers (8 ohm, 75w)
and Vintage 30 speakers (8 ohm, 60w) in diagonal way (X-pattern combination).
The purpose is to combine the different tones of these classic speakers into one cabinet.

G12T-75 speakers have more bass and piercing treble, mid-scooped sound.
Vintage 30 speakers have more midrange, smooth highs and lows are balanced.
Also, the Vintage 30 is much easier to breakup which gives it a more raw distorted sound.
Somebody like G12T-75 speakers very much, somebody hate them and love Vintage 30 speakers instead.

Vintage 30 frequency response chart :
http://professional.celestion.com/guitar/products/classic/index.asp


G12T-75 frequency response chart :
http://professional.celestion.com/guitar/products/classic/index.asp



Marshall 1960 Lead cabinet is a "stereo mode" cabinet,
but Bogner Uberschall cabinet has only mono input jack.

Tools :
Long Philips screwdriver or automatic screwdriver.
You need to unscrew total 17 long screws for removing the back panel of the cabinet,
so the automatic screwdriver will definitely help you a lot.


Pull out the jack plate, remember to label accordingly of that four speaker cables - two reds and two blacks.
Each pair of speaker cables (one red, positive and one black, negative) is connected with one pair of speakers
(2x12" speakers) from each left of right side in the cabinet.

Be careful ! Don't get confused with them because you need to connect them back again.


Remove the speaker cable connectors.


After the jack plate is removed, put your hand in and pull out the back panel of the cabinet.


You can see the stock Celestion G12T-75 speakers.


Marshall wires the four speakers in "series-parallel wiring" (16 ohm) or "parallel-parallel wiring" (4 ohm).
=Stereo and Mono Mode=
In "Stereo mode", each left or right side of the 16 ohm speakers are wired vertically in "parallel" wiring,
total impedance is 8 ohm for each side.

In "Mono mode", PCB circuit of the jack plate connects each left and right side of "parallel-wiring" speakers into either "series-wiring" (Total: 16 ohm) or "paralle-wiring" (Total: 4 ohm) again.

Marshall factory wiring diagram like below :