[Central-Electronics] Solid State Power Supply for 100V

[Jim candela]

	Peter,

	There are those who believe that a power supply has an audible effect on
how an amplifier behaves. By amplifier I refer to audio amplifiers with a
tube basis. Push pull circuitry is more forgiving than high end single ended
amplifiers when it comes to the source impedance (Rs) of the power supply.
Lets say from DC to 1 Khz the power supply Rs is 350 ohms, and decreases
steadily above that frequency as the filter capacitance reactance decreases
with rising frequency. This will continue until resonance occurs where Rs is
near zero, and then starts rising again. All of this can occur within the
high fidelity 20-20,000 hertz audio range. Any ripple on the power can also
have noticeable impact on the sound as well. One source of ripple is the
solid state rectifiers. This is where in  a dual diode (FW-CT) circuit the
diodes themselves at crossover simultaneously conduct. This momentarily
shorts out the transformer, and when the reverse biased the diode finally
gives up, and the transformer releases a big voltage spike large enough to
blow many diodes. I've seen the 1N4007 variety where the overlapping period
can be several hundred micro-seconds. A suitable R-C snubber can gobble this
up to no ill effect. I have an old W6SAI Radio Handbook where this approach
was suggested. I think that was the 1970 edition. Another source of ripple
where the audio amplifier modulates the power supply due to the high Rs of
the power supply. This can be very apparent with heavy bass notes that can
drain the power supply maybe 20% in a few cycles at 20 hertz.

        The audio amplifier example closely parallels what we're doing with
the 100V with the 6550's. The big difference is parallel operation at RF
instead of push pull at audio. We still wiggle the RF at an audio rate
(SSB), so this is still is applicable. For those interested, here is how I
tackled this issue on a Sherwood audio amplifier (tube, circa 1962) using
power supply refinements to try to lower Rs to near zero across the audio
range.

        http://pages.prodigy.net/jcandela/Sherwood_S8000/HV_REG/regulator.ht
m

Regards,
Jim
WD5JKO


-----Original Message-----
From: central-electronics-bounces at mailman.qth.net
[mailto:central-electronics-bounces at mailman.qth.net]On Behalf Of peter
markavage
Sent: Thursday, February 24, 2005 4:25 PM
To: central-electronics at mailman.qth.net
Subject: Re: [Central-Electronics] Solid State Power Supply for 100V


I solid-stated my 100V years ago. Found some old and weak tubes with
octal bases, broke the glass, cleaned out the base, epoxy a small perf.
board in it, mounted some 1N-4007's or something similar (bag of 100 for
pennies at a flea market), and plugged it in. Been working ever since. No
variac, no thermistors, no power resistors, etc. Most of my rigs have
something similar.

Pete, wa2cwa

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