THD Electronics Flexi-50 - Manual (Page 10)

THD FLEXI-50 INSTRUCTION MANUAL 10
4. Set your multi-meter to read DC voltage. If your multi-meter requires you to set a DC
Voltage range, set it to the lowest range that is above 100mV.
5. With no input to the Flexi, flip the Standby switch to Play.
6. Using a flat blade screwdriver, adjust the bias control for Tube 1 (C) — turn it slowly,
the control is very sensitive. If you are in 50w mode, set it to 0.025VDC; if you are in
20w mode, set it to 0.017VDC. (Please note: If your meter displays in mV rather than
volts, this may show as 25mVDC rather than 0.025VDC and 17mVDC rather than
0.017VDC. Read the manual for your multi-meter to be certain.)
7. Move the red probe of your multi-meter from the Tube 1 socket (B) to the socket for
Tube 2 (D).
8. Adjust the bias control for Tube 2 (E) the same way you adjusted the bias control for
Tube 1.
9. Leaving the red probe in the Tube 2 socket (D), move the black probe to the red socket
for Tube 1 (B). If the two are power tubes are balanced properly, you will get a reading of
0.00VDC (+/- 0.002VDC).
10. If you do not get a reading of 0.00VDC in step carefully adjust the bias control for
Tube 1 (C) until the reading is 0.00
NOTE: You won’t need to re-bias the amp if you are using EL-84 tubes in the THD YJS
or YJ20 Yellow Jacket adaptors, as they are self-biasing. If you are using EL84 tubes in
the THD YJUni Yellow Jacket adaptors, you will need to set the bias, since YJUni
Yellow Jackets are for amplifiers that are already self-biasing, such as the THD UniValve
and BiValve amplifiers. Remember to always set the Flexi-50 to “20W” when using EL-
84s with YJUni adaptors.
ALSO NOTE: As power tubes age, their bias requirements change. It is a good idea to
check and re-adjust the bias of the amplifier after every month or so of regular use. Also,
if you want to be picky, when you get to a gig, it is quite likely that the power in the
venue where you are playing is not the same voltage as where you rehearse, so it is not a
bad idea to check the bias in the venue and re-adjust it if necessary. This will ensure a
consistent sound from your amplifier.
Preamp Tubes
You don’t need to re-bias the amp to try out new preamp tubes—just pull out the current
tubes and inset a new one! The Flexi can take any type of dual triode preamp tube, such
as 12AX7, 12AY7, 12AU7, 12AT7, 12AZ7, 12DW7, 12BH7, ECC-83, ECC-82, ECC-81
and more. You can try any of the above tube types in any combination—remember,
experimentation is the name of the game!