AX40
and AX100
Introduction
The mid seventies brought some updates to the WEM ER and PA heads, with public address duties going to the AX and guitar to the GX series. They were soon overtaken by changes in the music scene and the 40watt versions don't seem to have lasted long. The AX was eventually joined/replaced by more versatile, multichannel powered mixers. Still useful for small bands and solo performers though, but (personal opinion) the tone circuits don't suit guitar like the old ER.
The 1975/6 catalogue extract below is courtesy of the WEM Owners Club at http://wem-owners.com/ . Lots of really interesting Watkins and WEM reference material.
Catalogue Specifications
Input Sensitivity:
Catalogue just says "high impedance" with no levels specified.
Bench test with volume at max and tone controls at 12o'clock:
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Input 1 - 6mV
-
input 2 - 12mV
-
Input 3 - 6mV
-
Input 4 - 12mV
If both inputs of either pair (1+2 or 3+4) are used, both inputs switch to 6mV.
Slave Output:
640mV @ 600 ohms
Power Output:
40watts into 8ohms (AX40)
100watts into 8ohms (AX100
Note - there is no mention of how the power is measured.
What you get at clipping with a 1kHz sine wave into a dummy load is:
-
33watts rms into 6ohms
-
28.5watts rms into 8ohms
Dimensions:
Both versions - 185/8"w x 71/8"h x 11"d
Weight:
AX40 - 18Ib approx
AX100 - ??
Price in 1975:
AX40 - £84.00 (about £625 in 2024)
AX100 - £110 (about £818 in 2024)
For a discussion about the Bulgin power connectors, have a look at the ER40 page HERE.
Preamp
As in the ER and PA series, the 40watt and 100watt versions share a common preamp, the one difference being the value of the series resistor feeding the zener voltage regulator. The new circuit gets an isolating capacitor on the slave output - no more DC.
WEM AX40 and AX100 Preamp Schematic
WEM AX40 and AX100 Preamp Board Layout
AX40 Power Amplifier
Electrically, the AX40 power amp section is the same as the ER/PA40s with a few updates to component types. Mechanically it's much simpler. Main features are:
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No mains voltage selector
-
A new circuit board with the output device power resistors on-board instead of on a tag strip
-
A grounding link to the speaker socket / mains input mounting plate
WEM AX40 Power Amplifier Schematic
WEM AX40 Power Section Layout
WEM AX40 Power Amplifier PCB Layout
AX100 Preamp
See AX40 Preamp section above.
AX100 Power Amplifier
Sorry, haven't got one to look at at the moment.