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R, -50 ohm wirewound pot.
R - 100,000 ohm, 2 w. carbon res.
R :- 25,000 ohm, 10 w. und res.
R,-25,000 ohms, 20 w. wirewound adj. res.
R :5-1000 ohm, SO w. wirewound res.
R0-500 ohm, 50 w. wirewound adj. res.
C,, C_ -- -1 pfd. oil -filled bathtub cond.
Ca -Cs, Ca -C;, C-C S/8 pfd.. 600 v. oil -filled
cond. (C,, -C, can be replaced by a single 16
pfd., 600 v. elec. cond.)
C :5-50 pfd.. 50 v. elec. cond.
C,5, -C-40/40 pfd., 150 v. elec. cond.
F,-4 amp, fuse (Littelfuse)
F.-1/ 30 amp. fuse (Littelfuse)
F,,-11/2 amp. fuse (Littelfuse)
CH,-20-4 hy. @ 300 ma. swinging choke
CH_.. CH. -10.5 hy. @ 110 sa. filter choke
CH, -4 i,v. 41) 200 ,na. choke
T, -Fil. trans. 6.3.v. @ 5 amps., c.t. (sec text)
trans. 5 v. í1i 6 amps
T,, -Power trans. 785.0 -785 v. @ 300 ma.
T, -Fil. trans. 6.3 v. @ 5 amps.
Tr,-Power trans. 375.0.375 @ 150 ma.; 5 v.
@ 3 amps.: 6.3 v. a 5 amps., c.t.
T -Plate trans. 100 -0.100 v. @ 150 ma. This
is a home constructed transformer and may
be substituted for a 117 -volt isolation transformer
providing a half -wave rectifier is used.
Rect. -300 ma. full -wave selenium rectifier
S,- S.p.d.t. toggle switch
M, -150 volt a.c. voltmeter
PL, -6.3 volt pilot lamp
V V .-SU4 tube
V :,-5Y 3 tube
V,- VR10S tube
Fig. 6. Power supply circuit. A separate chassis is used in order to reduce hum.
also became necessary to use two
6AS7G tubes to handle the 300 ma.
drain on this supply. The insertion of
Fig. 7.
Under chassis view of the power supply unit.
the plate and grid isolation resistors
R0, R, :, R,, R0, and R,.,, R,., R, :, R.o
serves to uniformly distribute the
Fig. B.
plate current on each individual plate
and to eliminate any possibility of oscillation.
Because the cathodes are 450
volts above ground, it became necessary
to raise the heaters so that the
heater- cathode potential would not exceed
the rated 300 volts. The most
convenient was' was to use a separate
heater transformer for the 6AS7G
tubes and return its center tap to the
cathodes of the 6AS7G tubes. This
gives a zero voltage between heater
and cathode at all times. A word of
caution -when working around inside
of the amplifier or power supply, remember
that these 6.3 volt heaters
are actually 450 volts above ground
and should therefor be considered
highly dangerous.
Because of the zero impedance of
this supply, if anything goes wrong
in the circuit, something is bound to
snap. For this reason one should not
attempt to eliminate the fuses that
are indicated on the diagram or increase
their current ratings.
The panel meters could have been
excluded from the circuit but they
are a convenience when making any
adjustments in the voltage regulator
or balancing the output stage as the
tubes deteriorate. When the voltage
regulator was added and the changes
made in the Childs' amplifier a preliminary
test proved that the circuit
was now entirely satisfactory for the
author's needs. The amplifier was then
dismantled and reconstructed as shown
in Fig. 1 (left). The voltage regulator
was included on the amplifier chassis
as it was convenient to have all of the
pertinent controls located on one
chassis. The tubes and components
were located in such a manner as to
maintain balanced lead lengths on
each side of the push -pull circuit. The
grid and the plate leads are virtually
point -to-point wiring even though the
resistors are placed on resistor cards.
The only leads that are cabled are the
ground, plate supply, and heater
leads. This method of construction
makes it simple to check, to replace
any component, and to locate any difficulties
that may occur at some
(Continued on page 102)
Top view of the husky, 83 -pound power supply.
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