Octave V 70 Class A, Owner'S Manual

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11. TROUBLESHOOTING
11.2 Faults caused by tubes
Like other OCTAVE products, the V 70 Class A is equipped with a double safety system. This
means that the amplifier will be protected from damage if a component (tube) should fail and trip
the electronic protection. The protection system protects the amplifier and the tubes from overload.
This technology has proven its worth in recent years.
It has enabled us to reduce our overall failure
rate (except for output tubes, which we are unable to control 100 percent) to virtually zero
.
OCTAVE equipment will achieve a service life of 10 to 15 years without needing to be serviced.
We
feel that this is particularly important aspect of tube equipment design, as many preconceptions still
exist about the technology's durability and long-term stability.
There are a number of reasons why tubes might fail at some point in their lifetime. You can fault-
find tubes by examining their behavior.
Mechanical fault that does not trip the V 70 Class A's protection

The tube's heater filament no longer glows
No matter whether it is a driver tube or an output tube, no tube can work without a properly
functioning heater.
Output tube heater fault
When the heater system on an output tube fails, you will be unable to adjust the BIAS. The
particular tube will refuse to move from the minus setting. A loose connection inside the tube could
have caused the heater to fail. It may be possible to repair the connection by mechanical means. If
the BIAS was previously badly misadjusted, the BIAS might "run-away", tripping the electronic
protection.
This is why you should never turn the BIAS screws to the extreme right and leave them there. If
you have not been able to adjust the BIAS satisfactorily, turn the adjuster screw back to its extreme
left position.
Driver tube heater fault
When a driver tube heater fault occurs, you will normally lose an entire channel (depending on
which driver tube system is affected by the faulty heater). This can only be established by a visual
examination. The heater filaments are often difficult to see inside the driver tubes, since they only
protrude very slightly from the tube system. OCTAVE uses double triodes exclusively, i.e. there are
always two identical tube systems within the glass envelope. Because each of these triode systems
has its own heater, you should always be able to see two glowing filaments. If you can only see
one, it means that the tube is faulty.
 A tube has developed an air leak
The glass envelope of all tubes normally contains a vacuum. In order to maintain the vacuum
throughout the service life of the tube, there is a device inside the tube that absorbs the residual
gas. It is called the getter pill. It normally takes the form of a small crucible near the top of the tube.
It contains a substance known as the getter, which absorbs and permanently retains the residual
gas. This device ensures that the tube maintains a high vacuum during its entire service life.
Hairline cracks around the base and leaks around the socket pins can cause the tube to take in air.
Because the getter is only able to absorb a finite amount of gas, it will soon stop working. The silver
coating at the top of the tube will then begin to discolor. If a tube has an air leak, you will not be
able to adjust its BIAS voltage. As soon as a certain amount of air leaks into the tube, it will stop
working completely and the heater filament will burn through.