The Fender 400-PS Updates & Mods

The Fender 400-PS Updates & Modifications

1. Please look carefully at this tube layout sticker which is found inside the cabinet of the 400-PS amplifier. It is very *IMPORTANT* to note the use of the 12AU7 vacuum tube for the position of V6.
For some reason the only schematic made available for the 400-PS by Fender mistakenly shows a 12AX7 being used for V6. To use a 12AX7 for V6 gives the over all impression, that the 400-PS can not reach the full rated output power because of the premature clipping seen on the test loads.
This mistaken impression by many amp techs, leads to thinking the 400-PS is greatly over rated, and there is no way the 400 can reach it's advertized full power output rating.
When using a good USA made 12AU7 for V6, as the tube layout sticker shows, you will find the 400-PS can produce a lot MORE than its advertized rated power output.
The only proper tube to use for V6 in the 400-PS is the USA made 12AU7.

2. For those of you who can't get used to the idea of a 12AU7 vacuum tube being inside a Fender amplifier, there is an answer.
Just change the 12K 2 Watt resistor on V6 to a 22K 2 watt resistor.

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