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

[Jim candela]

Lyman,

    The manufacturer states the following, "It is a combination of diodes,
power resistors, and other circuitry that emulate the warm-up and operating
curve of the tube type rectifier it replaces. Each model emulates the
forward conduction resistance curve of the tube type it replaces and also
has linear in-rush current limiting to simulate the warm-up of a tube
rectifier, however, it is in the 1 to 2 second range, rather than the 7 to 9
seconds of a typical rectifier tube."

    To me this implies he uses suitable diode(s), a series power resistor,
and a negative temperature coefficient thermistor in parallel with the power
resistor. My guess is that he uses the copper top as a heatsink for the
power resistor. Maybe my guess is incorrect. If someone knows the details,
please jump in and clarify the situation. This is a clever marketing
strategy, and it will probably work just fine in many applications.

     One thing concerns me here. The stated 1-2 second warm-up is faster
than the original rectifier if it were indirectly heated. It might be
comparable to say a 5U4 which is directly heated, and will supply B+ very
quickly after turn on. I worry about the power supply electrolytics where
the surge voltage may be higher than with a vacuum tube rectifier. This
surge may damage the filter capacitors if too high.

     I have observed poor power supply performance in rigs like the EF
Johnson Viking I where the B+ may sag a 100 volts or more with modulation
(AM). Converting the P/S to solid state really wakes this rig up with higher
B+, and much stiffer regulation. As for the 100V / 200V I believe the stock
design is "higher-end" than what Mr. EF Johnson used in the Vikings. I am
not sure what advantage if any this proposed power supply change would do
for a 100V. If the surge, or B+ is higher, the filters might be at risk, and
the 6550 pin 3 (plate) may flash over to ground.

     If you go ahead to try this copper rectifier, please take some time to
evaluate stock versus modified performance, and report back to the group.

Thanks for getting a topic going again,
Regards,
Jim Candela
WD5JKO


-----Original Message-----
From: central-electronics-bounces at mailman.qth.net
[mailto:central-electronics-bounces at mailman.qth.net]On Behalf Of Radra
Sent: Thursday, February 24, 2005 11:42 AM
To: Central Electronics
Subject: [Central-Electronics] Solid State Power Supply for 100V


I am considering replacing the tube rectifiers, 5U4-GB and 6AU4-GTA, with
solid state rectifiers.  Weber manufacturers a series of plug-in
replacements for these tubes e.g. "Copper Cap Rectifiers".  Their
performance is supposed to emulate that of the original tubes.  Refer to
http://www.webervst.com/ccap.html for more info.

Has anyone had any experience with these replacements?  Or more generally,
are there any recommendations regarding use of solid state in the 100V power
supply?

Lyman K7LH

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