[Milsurplus] Strong Stomach Needed.

[Bruce Lane]

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..."