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Regulated HV B+ Supply for Preamps (modeled on Vorhis/Jung PAS
Modification)
This circuit is shown in several incarnations, using an LM317 as the
error amplifier and a MJE3439 or BU208A PASS transistor. Jung used
photoflash capacitors in their article "The Last PAS" (The
Audio Amateur 4/82 pp 24..30). The regulator was discussed at lenght
and used previously in the Marantz 7 modification by Walt Jung and
Chuck Hollander: "Modifying the Marantz 7C or St.
Pooge and the DRIAAGON" (The
Audio Amateur 1/81 pp 20..37).These are reportedly very low
ESR. A pair of 680uF/330V were used
instead of C1. In this example Panasonic type UP which
are quite compact and relatively inexpensive are used. WIMA type
MKP (or other) polypropylene
capacitors are used at C2. C3, C6 and C7. In the original article,
R1 was 27kΩ 1W. In a subsequent
correction, 39kΩ 1W was used for better
performance. Resistor R3 (nominal 100Ω) may
be adjusted such that the zener diode string D6..D8 is biased at 12mA.
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| The Printed Circuit Board
is shown below. The boards to may be
split apart -- necessary if this is going to be used in
the PAS, where headers HDR1,2 and 3 are located. Use a
pair of tin snips or aircraft sheers to make the cut.
I incorporated some suggestions from participants
on the DIYAUDIO board, including the possibility of full wave
rectification and resistors in the leads (RS1, RS2 and
RS3) to the large filter capacitors. These can be jumpered
(and they are jumpered in my
version.) Note that there is a ground plane on the bottom
foil of the PCB. This ground plane can be attached to the
output ground connector where indicated, or at the negative pin
of C5.
Transistor Q1 requires a heat sink of at
least 3 square inches. I have found that the LM317HV works
better than the LM317 -- I don't know why this is the case as
the voltage across the regulator should be limited by D4.
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Printed Circuit Board for HV Regulator |
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Assembled Regulator
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| So How Well Does it Work?
Below is a snapshot of the input and output on my Tek 2465 --
the input is from an unmodified Heath IP-17 Regulated Supply,
400VDC. In each case the scale is 20 millivolts. The
load was a 50k resistor.
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The chart below
illustrates the Last PAS Regulator noise -- the noise was measured
with a 3Hz bandwidth on a Hewlett Packard 3581 Selective Level
Meter.
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