HP Aikido Stereo 9-Pin PCB - Manual (Page 5)

GlassWare Audio Design
4
Heater Issues
The board assumes that a DC 12V power supply will be used for the heaters, so that
6.3V heater tubes (like the 6FQ7 and 6DJ8) or 12.6V tubes (like the 12AU7 or 12AX7)
can be used. Both types can be used exclusively, or simultaneously; for example 6GC7
for the input tube and a 12BH7 for the output tube. For example, if the input tube (V2
and V3) is a 12AX7 and the output tube is a 6H30 (V1 and V4), then use jumpers J1, J5
and J6.
6V Heater Power Supply Although designed for a 12V power supply, a 6V heater
power supply can be used with the PCB, as long as all the tubes used have 6.3V heaters
(or 5V or 8V or 18V power supply can be used, if all the tubes share the same 5V or 8V
or 18V heater voltage). Just use jumpers J1 and J4 only. Note: Perfectly good tubes with
uncommon heater voltages can often be found at swap meets, eBay, and surplus stores
for a few dollars each. Think outside 6.3V box. (A 25V heater power supply can be
used, if only 12.6V tubes are used. Just use the jumper settings that are listed on the
PCB for 6V use. For example, if the input tube [V2 and V3] is a 12AX7 and the output
tube is a 12AU7 [V1 and V4], then use jumpers J1 and J4. )
AC Heaters An AC heater power supply (6.3V or 12.6V) can be used, if the heater
shunting capacitors C7, C8, C9, C10 are left off the board, or are replaced by 0.01µF
ceramic capacitors.
5 4 5 4 5 4 5 4
C7 C8 C9 C10
V1
V2 V3 V4
J1 J2
J3
J4
J5 J6
+H -H
Filament Jumper Wire Schedule
Use J2, J3, J5, and J6 only
and all tubes must be
6.3V types.
With a 6.3V PS
Output Tubes V1 and V4:
If tubes are 6V, use J1 only.
If tubes are 12V, use J2 and J3 only.
Input Tubes V2 and V3:
If tubes are 6V, use J4 only.
If tubes are 12V, use J5 and J6 only.
With a 12.6V PS
Do not use capacitors, C7, C8, C9, or C10 with an AC heater PS
Since one triode stands atop another, the heater-to-cathode voltage experienced differs
between triodes. The safest path is to reference the heater power supply to a voltage
equal to one fourth the B+ voltage; for example, 75V, when using a 300V power supply.
The ¼ B+ voltage ensures that both top and bottom triodes see the same magnitude of
heater-to-cathode voltage. The easiest way to set this voltage relationship up is the
following circuit: