14
2)
Plug a black probe into the color-coded jack on your DMM, and do the same for a red probe
3)
Insert the black probe tip into the black probe jack (yellow arrow). This is GROUND in the King Kong amplifier.
4)
Insert the red probe tip into the V6 red probe jack (green arrow) on the far left. This measures bias for V6.
5)
Adjust bias adjustment (blue arrow) SLOWLY until your DMM reads approximately 35mV (see calculations, following
page)
6)
Remove the red DMM probe tip from the V6 red probe jack (green arrow), and insert into V7 red probe jack (one to the
right). This measures bias for V7.
7)
Compare bias reading, and repeat for V8 and V9.
To calculate bias, there are two pieces of information you need to know: your amplifier’s power tube plate voltage, and the
published value for maximum plate dissipation for the power tubes used in your amplifier. To save you some time and energy,
here are those two values:
-
Approximate V6-9 plate voltage for King Kong 100W/50W amplifiers
=
460-470VDC
-
Maximum plate dissipation for EL34s
=
25W
…and now some math. The formula for calculating bias is as follows:
𝑚𝑎𝑥𝑖𝑚𝑢𝑚
𝑝𝑙𝑎𝑡𝑒
𝑑𝑖𝑠𝑠𝑖𝑝𝑎𝑡𝑖𝑜𝑛
𝑎𝑚𝑝𝑙𝑖𝑓𝑖𝑒𝑟
𝑝𝑙𝑎𝑡𝑒
𝑣𝑜𝑙𝑡𝑎𝑔𝑒
×
𝑝𝑒𝑟𝑐𝑒𝑛𝑡
𝑜𝑓
𝑚𝑎𝑥𝑖𝑚𝑢𝑚
𝑑𝑖𝑠𝑠𝑖𝑝𝑎𝑡𝑖𝑜𝑛
×
1000
=
𝑏𝑖𝑎𝑠
𝑐𝑢𝑟𝑟𝑒𝑛𝑡
(
𝑚𝐴
)
In most cases, amplifiers are biased between 50% and 75% dissipation. We bias the King Kong to approximately 35mV on a
DMM, which is 65% dissipation.
