Power Tube Rolling
The output tube sockets of the D
₂
O Amplifier are wired in such a way that they
are compatible with both 6L6GC and EL34 power tubes, as well as many similar
tube types with compatible pin outs. Thanks to cathode biasing, there is no need
to rebias the power amp when swapping tubes.
Different tube types do sound different from one another, and a little
experimentation can open up some new and different possibilities. The extent to
which this might be worth it to you depends somewhat upon how you use the
amp. If you tend to play clean, differences between different tube types will tend
to be subtle. The harder you push the output tubes the more the differences
among tube types becomes apparent—with different tube types having distinctly
different breakup characteristics.
Some tubes that are known to work include: 6L6GC, EL34, E34L, KT66, KT88,
KT120, 6550, and 7581.
Avoid 6L6GB or 6L6GA, as these are not rated for the power or voltage
seen in the D
₂
O circuit and may fail catastrophically in the worst case and
just not last as long in the best case.
There are no current production tubes
of this type, so you would only encounter these among vintage tubes. Our advice
is to save your vintage and new old stock tubes for circuits that are specified to
use those tubes.
7591s are not pin compatible, nor would they work in this circuit unmodified even
if they were.
6V6s cannot handle the conditions found in the D
₂
O and
should never be used.
Routine Maintenance
The D
₂
O Amplifier doesn't really require much in the way of routine maintenance
and should be able to be used for years at a time without doing anything.
The following are things you are likely to encounter:
Replacing Tubes
The most common maintenance task is replacement of the vacuum tubes, as
these do wear out or intermittently fail. To replace the tubes, power off the
amplifier and let the amplifier sit long enough for the tubes to cool off enough to
be handled.
Power tubes get quite hot in the course of normal operation
and can cause serious burns if handled while hot.
Once the tubes have
cooled, remove the amp's lid by removing the four screws that hold the lid onto