HP 9-Pin User Manual download pdf (Page 5)

GlassWare Audio Design

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 exa

mple 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: Perfec

tly 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 12.6

V) can be used, if the heater

shunting capa

citors C7, C8, C9, C10 are left off the board, or are replaced by 0.01µF

ceramic capacitors.

C10

J1 J2

-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 supp

ly.

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:

1 2 3 4 5 6 7 8 9 10 11 12 13

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HP 9-Pin User Manual Page 5

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