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Blown
valves in valve amplifiers
A blown valve is by far the most usual cause
of valve amplifier problems. Valves can blow at any time and can last
years or months. If you have problems with your valve amplifier always
check the valves first.
Please
make sure the amplifier is NOT connected to the electricity supply
before removing or installing the vacuum tubes.
If you are removing valves, wait until they have cooled down before
attempting to remove them.
What do
you see if a valve blows?
1.Valves can be quite dramatic if they blow
with loud crackling noises
and a very bright glow from the valve as the valve consumes itself.
2.A valve can also blow with little or no visible effect.
3.Sometimes, if the vacuum in the valve is lost through tiny hairline
cracks, you will see that the silver coating on the inside top of the
valve will disappear or go clear.
example of a
blown KT88
example
of a blown KT88 valve
on the right next to a new KT88 valve on the right
Smaller pre-amplifier valves
When one of the smaller pre-amplifier valves
blows it is likely the
amplifier will continue to operate, however, you will only hear sound
from one speaker.
Installing and removing valves
To remove a valve, use a dry cloth to grip
the old valve by the base,
pull the valve vertically upwards. The valve is simply pressed into the
valve holder so there should be minimal resistance.
It is common for a blow valve to also blow
the internal fuse, when this
happens the amplifier will not turn on and there will be no blue light
on the front panel the internal fuse is located in the power socket on
the rear of the amplifier.
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