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valves/tubes or re-bias the amplifier if the law forbids this. In this case, please ta
ke you’re
your amplifier to a qualified and approved electronics technician.
In certain countries it is also totally forbidden to keep or place any liquids on top of the
amplifier, (e.g. beer, water bottles, glass, drinks etc). This may cause serious electric
shocks and/or dangerous situations.
Also, it is totally forbidden to use the amp in the event of rain splatters/water drops
getting into or onto the amp.
Even if it is not a law in your country, you should never allow liquids near the amplifier or
attempt to use the amplifier if it has been subjected to any moisture as this could result
in a fatal electric shock.
Biasing:
Biasing needs to be done each time the output valves are replaced and should be checked
periodically to make sure they are working at their optimum for sound quality & valve
life. To set the Bias on the V140 you need a multimeter set to the 200mV DC range.
Biasing is carried out externally so no need to remove the amp from the wooden sleeve.
Output valves can be replaced from the rear of the amp by simply removing the back grill
and carefully sliding off the valve spring retainers. We recommend the use of a soft cloth
or heat-proof gloves to remove valves if possible. The valves can then be pulled out using
a slow rotational movement, (dweezling) to ease them from their sockets. This will free
them with the least amount of effort and stress. Ensure that the key on the replacement
valves lines up with the keyway on the socket before carefully pushing them home. Take
care when removing any valve as the pins can easily be bent and the plastic locating key
on the output valves can be snapped off. Make sure that they are never more than a few
degrees from vertical to avoid bending or breaking pins etc.
Always buy matched pairs or quads of output valves or Biasing may be difficult if not
impossible.
To Bias the new valves, make sure the amplifier is connected to a speaker cabinet, (or
dummy load resistor). Turn all controls to zero and remove the guitar input as any signals
may interfere with the Bias settings. Switch to High power using the rear toggle switch
and then into PREHEAT mode using the front toggle switch. Wait 60 seconds and then
switch to ON.
Now put the black meter probe, (-ve) into the Black centre GND Bias socket and the red
meter probe, (+ve) into the left hand V7+/V8+ Bias socket. Using a small flat blade
screwdriver in the Bias adjustment POT, turn this so you get 34mV on the multimeter.
This equates to 34mA of current per valve as we are measuring the voltage across a 1
Ohm resistor.
Now put the red meter probe into the right hand V5+/V6+ Bias socket and measure the
voltage. Try to balance the 2 measurements around 34mV with a maximum of 6mV
