[Milsurplus] Strong Stomach Needed.

[J. Forster]

Phase converters are available for reasonable prices. You don't need
perfect three phase to rectify to make DC.

The drive level issue could be solved without modification with a Narda or
other coax power attenuator.

-John

================



> Good day,
>
> *********** REPLY SEPARATOR  ***********
>
> On 15-Jul-09 at 11:25 Michael Tauson wrote:
>
> 	(snippage)
>
> I love the purists.  I really do.  Pretty
>>much like I love a rabid pit
> bull.  If it isn't NOS, NIB or an
>>exceptionally close approximation,
> it's just not worth having - or so they
>>say.
>
> 	(more snippage)
>
> At the same time, I do what I can to preserve what I can
>>but in fully
> functional form.  That sometimes means going in and *gasp*
>>actually
> having to do soldering et al.  Real work kind of stuff.
>
> 	(final bit of snippage)
>
> 	I have to agree, up to a point. There's absolutely nothing wrong with
> wanting to put together an original-condition radio setup from, say, the
> 50's or 60's. Many have already done it, and I suspect many others will
> do it.
>
> 	HOWEVER - When the desire to do so reaches a point of bashing anyone who
> makes mods to a radio to make it useful for their application, you're
> venturing into the territory of trying to force your beliefs on others,
> and that's not a Good Thing.
>
> 	Permit me to cite an example. I have, sitting in my garage, a gorgeous
> Harris HF kilowatt linear amp (the RF-110A, to be exact). I want to use
> it, but finding a means to generate the necessary final plate voltage
> (2250VDC at an amp) has been challenging. Yes, it came with a power
> supply, but the thing requires three-phase utility input (unavailable in
> my area). Also, the amp itself requires 100mW of drive, unmodified, which
> is incompatible with my radios (100 watts output is typical).
>
> 	If I were to go the "purist" route, I would probably have to take out a
> second mortgage for Puget Sound Energy to run in a polyphase feed, or get
> hold of a single-to-polyphase rotary converter. Either way, the cost
> would range into the mid-to-high four-figure arena, and I simply don't
> have the room for one of those rotary monstrosities.
>
> 	I've tried to locate the single-phase supply for this amp (they're
> exceedingly rare), but every one I've seen went for over $300 WITHOUT
> shipping, and they're heavy enough I'd have to shell out for truck
> freight costs. That's over twice what I paid for the amp itself.
>
> 	Even if I did go that route, I'd be surprised if I got better than, say,
> 40% efficiency out of it. Face it, it's a transformer-based design done
> in the late 60's/early 70's. Technology has improved a bit since then.
> ;-)
>
> 	The solution I found is twofold: First, for the plate voltage, scrap the
> three-phase supply completely, and replace it with a high-efficiency SMPS
> design I found in some back issues of QEX. The entire HV plate supply
> will then easily run from a 240V single-phase input, drawing less than 12
> amps, and tip the scales at around eight pounds. The remainder of the
> specialized supply circuits in the existing power supply, such as the
> 400Hz source, will run perfectly well off single-phase 120VAC.
>
> 	And, getting rid of that horrendously heavy three-phase potted
> transformer will make the power supply chassis at least 80 pounds
> lighter.
>
> 	Second: Modify the amp itself by bypassing the driver stage, and feeding
> the final tube directly. I've already got the details on doing so tucked
> away on my hard drive somewhere. That also eliminates at least two other
> voltages I'd normally have to supply.
>
> 	In essence: What I'm doing is making good use of older technology, which
> might otherwise have been scrapped and melted down, but taking advantage
> of newer technology to do it. How is that harmful to anything or anyone?
> Does the fact I can't afford to use it in original/unmodified condition
> make me a "bad person?"
>
> 	Looking at the bigger picture: How much power would I be wasting if I
> tried to use it unmodified? How much extra pollution might that generate
> from the power plant(s) supplying my part of the grid? Does it not make
> sense to be as efficient as possible, even when using older stuff? How is
> seeking a balance between old and new wrong?
>
> 	I'm sure there will be purists Out There who will cringe at the thought
> of any mod to equipment like this. If so, well... I'm sorry you feel that
> way, but at least I'm trying to put a well-built piece of gear to use, in
> as much original shape as possible, rather than stripping it down to a
> bare chassis and building my own design into it.
>
> 	Happy tweaking.
>
>
> -=-=-=-=-=-=-=-=-=-=-=-
> Bruce Lane, Owner & Head Hardware Heavy,
> Blue Feather Technologies -- http://www.bluefeathertech.com
> kyrrin (at) bluefeathertech do/t c=o=m
> "Quid Malmborg in Plano..."
>
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