[Boatanchors] Solid-Stating a Johnson Valiant Power Supply

[Dave Harmon]

Hello Cousin......
I've got a nice Valiant 1 that I recapped and made serviceable.
I used 3B28 rectifier tubes in place of the 866....they don't have a warm up
time and no mercury either.
I would use the LV power supplies as designed...you won't have to use
voltage dropping resistors and tubes will avoid the huge startup surges that
can't be doing those transformers any good.
Make sure to use the capacitance values shown on the schematic and parts
list. If you increase cap value the voltage will go way higher and could
cause problems.
I would return it close to original as possible....not because I am a
purist...far from it...but my stuff has to work as designed unless there is
a real need to change it.
You won't be able to find parts that are similar to the originals so you may
have to use several caps in series or parallel to get the correct values.

Dave Harmon
K6XYZ[at]sbcglobal[dot]net
Sperry, Ok.


-----Original Message-----
From: boatanchors-bounces at mailman.qth.net
[mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of Michael D. Harmon
Sent: Monday, September 10, 2012 6:56 PM
To: boatanchors at mailman.qth.net
Subject: [Boatanchors] Solid-Stating a Johnson Valiant Power Supply

I recently became the proud owner of a very nice Johnson Valiant
transmitter.  I've done the normal cleanup and tube checking stuff, and the
next step will be capacitor replacement.  The transmitter has had the 866A
rectifiers replaced by a pair of RCA CR-105 diodes epoxied into a couple of
4-pin tube bases.  Since the old HV rectifier tubes are already gone (and I
really don't want all that mercury around anyway), I'm thinking about
solid-stating the remaining power supplies as well.

I'm sort of ambivalent about this project.  I've always been hesitant about
making major mods to a piece of vintage gear, but I'm planning to actually
use the Valiant, so preserving its life as long as possible is more
important to me than maintaining its "vintage vibe".

I've heard comments from both sides - I've been told to solid-state all the
power supplies, and I've been told to leave the power supplies alone.  I
know converting the power supplies will bring up the B++, but I plan to
recap the entire transmitter anyway.  I plan to use poly film 630V caps for
all the tubular replacements, and 450V caps for the electrolytic
replacements.

By eliminating the filament wiring, I should relieve the LV transformer of
some filament current, as well as the HV running on the filament leads.  I
should also eliminate some heat in the cabinet.

Other than the caps, What else can I damage by increasing the B++?   Are 
there other areas I should be careful of?  I don't anticipate any problems
with the chokes or the mica and ceramic caps, but there may be other things
I'm not aware of which could jump up and bite me!

I would really appreciate any suggestions, tips, warnings or helpful
comments from anyone who has done the conversion to solid state.  Oh, and
BTW, I'm not all that sure about those CR-105 diodes which were used to
replace the 866A's.  I found them listed in a 1963 Allied Industrial catalog
for $22.40 each, but there's no other documentation on them. 
They say 5000 PIV, but they have to be at least 50 years old.  I'm a little
dubious about how well they would hold up if I start using the Valiant a
lot.  Should I replace them with some commercial 866A replacement diode
stacks or possibly a few 1N5408's with 470K resistors and .01 uF caps across
each diode?

Thanks!
Mike, WB0LDJ
mharmon at att dot net
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