TUBES
Page 6
The LA-1 uses Cool-Swap™ technology to let
the tubes run cooler and provide a built-in
spare.
Many dual triodes, including the 5687, have
split heaters, allowing them to run from either
6.3V or 12.6V. This heater set-up allows only
one of the two triodes to be heated. In the
Cool-swap configuration, one tube is used
for each channel, each with one half heated.
The right channel uses triode #1 and the left
channel uses triode #2. Since the main failure
mode in modern tubes is cathode wear-out,
the unused triode in each tube is essentially a
spare. By swapping the two tubes, the unused
spare is brought into use. Thus Cool-Swap
effectively doubles tube life, and since only
half the tube is heated, the tube runs cooler,
an important factor in the normally hot-run
-
ning 5687. A side benefit is reduced cross-talk
between channels, since each channel has its
own tube.
One effect of the Cool-Swap technology is that
only one half of each tube will be “lit-up”. This
is normal in the LA-1.
How often you have to swap tubes, or replace
them with new tubes if already swapped,
depends on how you use the LA-1. The
5687WB tubes supplied with the LA-1 should
last several thousand hours of active use. Signs
that the tubes are weak include: less gain than
usual, a “flabby” sound, excess noise, and a
weak reading on a tube tester.
Since the LA-1 uses a soft heater turn-on and
delayed application of high voltage, tube life
-
time is not degraded by power cycling. Thus,
it is recommended that the LA-1 not be left
on all the time, but only be turned-on when
needed, with perhaps a one-half hour warm-
up time, if desired.
Tube Types: The tube manufacturer and tube
type will have an effect on the sound of audio
equipment. The LA-1 was designed for the
6 Volts6 Volts
No
Co
nnection
No
Connection
A B
B
A
6 Volts6 Volts
No
Co
nnection
No
Connection
Cool-
Swap
TM
Left Right
American 5687 tube, originally developed by Tung-Sol (the
same manufacturer that developed the 5881 and 6550). This
tube is no longer manufactured, but large quantities are still
available as “N.O.S.” (New Old Stock). The 5687 was used in
industrial and military equipment and as a result, nearly all
tubes available are built to higher quality and reliability stan-
dards than tubes for consumer equipment. The 5687WA and
5687WB are later versions with tighter control of their charac-
teristics.
Although not identical in characteristics to the 5687, the fol
-
lowing tubes can also be used in the LA-1: 6900, 7044, 7119,
and E182CC. If you try these, listen carefully to the sound,
and only use the types that sound the best. The LA-1 was
optimized for the 5687, however.
Warning: Do not use any other types of dual triodes. The
pin connections of all other dual triodes are different and
damage to both the tube and the LA-1 will occur if used.
Artemis Labs is not responsible for damage caused by using
incorrect tubes!
