[Milsurplus] Strong Stomach Needed.

[Bruce Lane]

	You and I most likely have a different definition of "reasonable." ;-)

	In any case, it's academic. I will likely be winding the transformer for the SMPS this fall. That, and the drive mod is easily made and easily reversable. Why waste power in an attenuator when I can put it to good use in driving the big tube?

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On 15-Jul-09 at 15:53 J. Forster wrote:

>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,
>>
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>>
>> 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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-=-=-=-=-=-=-=-=-=-=-=-
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..."