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The PZ8 will drive 240's fully (if it's voltage is reduced to 35) into
any impedance, and will drive the 260 at full power into BQ.
However, into 4{lthe PZ8's current limit starts to operate to give
extra orotection. the full 40 + 40w will not be reached with both
c h a n n e l s d r i v e n s i m u l t a n e o u s l y .
Thus in the table below, expected output powers are given for
various combinations of power supply. Columns 1 t 2 apply to 240
butwon't be affected much bv use of a 260. Column 3 is with a PZ8
set at 35v, with 240 or 260 (260 here will show increased power into
4Q, of 25 & 25w). Column 4 is a normal PZ8 at 50v with 260's.
3 .
4 .
PZB
PZg
reduced 50v
2 0 + 2 0 3 0 + 3 0
t z + t z
z 5 + z 5
7 + 7
1 4 + 1 4
20
45
t z
z 5
7
1
4
B o t h c h a n n e l s d r i v e n 4 Q
8 A
1 5 0
O n e c h a n n e l d r i v e n 4 O
8 0
1 5 [ )
1 .
2 .
PZs
PZ6
6 + 6
1 1 - F 1 1
4 % + 4 Y , 1 2 + 1 2
3 + 3
7 + 1
8
2
0
5 %
1 3
4
l
EA/ EB PZ' 8 PZ6
EA1
PZS Description
The PZS consists of a centre tapped transforrner feeding a full-wave
rectifier with a 2000pF reservoir capacitor, to give a no-load output
of approx. 28v.
The transformer has a twin primary for series/parallel operation on
220v or 1 10v ranges.
EB1 PZ6 Description
The PZ6 uses the same transformer as the PZ5 but feeding a bridge
rectifier to give approx. 56v dc on the 1000pF capacitor.
At switch on, there is no voltage on the output, but the voltage on
the junction of R1 I
R2 forward biasis D1, slowly charges up C2.
Tr4's base rises and it passes slowly increasing current to Tr3 I Tr1.
The output voltage starts to rise until about 9v when ZD1 becomes
forward biased.
Tr4 now compares the zener voltage on its emitter with a
proportion of the output voltage fed back from VR1, and adjusts
drive to Tr1 I 3 to stabilize the output voltage dependant upon the
s e t t i n g o f V R 1 .
Fs1 is a fuse to give some protection and this will infact blow after
a few seconds on a heavy overload if 3 or 4 speakers are in use.
lf a direct short circuit occurs across the output however, transi-
stors mav fail as well as FS1
so if the fuse has blown the rest of
the circuit should be tested before replacing.
To test the circuit disconnect it: + I - outputs, replace FS1 by a
1a slow blow and switch on, with a voltmeter across the output. The
voltage will rise quickly to about 15v and will then slow down,
stopping at 35v. VR1 should now adjust the stabilized voltage
between 20 and 50v approximately.
EA5 Connections
EA5.1. Mains conneutions
Live (L) and neutral {N) are connected via appropriate switches and
fuses to L 8 N on the PZ5/P26. Earth connects either directly or
indirectlv to the chassis (-ve terminal).
E A s . 1 . 1 . F u s e a n d s w i t c h
Whilst the output (dc) of the power supplies does not require f urther
EA 2
PZS circuit
EB 2
PZ6 circuit
protectlon it is strongly recommended that a fuse be inserted in
series with the mains connections to the transformer. For PZ5 and
PZ6 this can be 250mA anti surge. For the PZ8 transformer it should
be 500mA anti surge.
lf the fuse also provides power to other equipment (e.9. the
turntable motor) then this rating will need to be further increased.
A two pole switch should be used in the mains to provide
complete isolation.
EA5.1.2. 1 10v operation
To change from 22Ov to 110v the red and pink wires from the
transformer (at present connected to land B in fig. EA.3) should be
unsoldered. Now connect the red wire to the same land as is
connected the mauve wire, and connect the pink wire to the same
l a n d a s i s c o n n e c t e d t h e o r a n g e w i r e .
F o r 1 1 0 v o p e r a t i o n t h e f u s e r a t i n g s h o u l d b e d o u b l e d .
To change from 1 10 to 220v the above procedure must be
reverseo.
EA5.2. Output
Output of the PZ5,/6 is between + &
terminals. The - output is
isolated from the chassis.
EA10
Common faults -
PZ5
The PZS's circuitry is so simple that there is very little to go wrong
with it and it will even survive a short circuit across its output for
some period.
Overheating lf the transformer gets hot it is usually because one of
the amplifiers is at fault. Disconnect both Z40s and when the PZ5
has cooled down switch on again. The PZ5 should remain cool.
Faulty diode. Occasionally one or other diode may fail open-circuit or
short circuit. Open circuit failure will cause an increase in hum level
( a n d a h u m f r e q u e n c y c h a n g e f r o m 1 0 0 H z t o 5 0 H z ) b u t m a y n o t b e
noticed. A short circuit diode will cause overheating. Both con-
EA 3
PZ5 layout
27
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