[Milsurplus] Strong Stomach Needed.

Wed Jul 15 19:17:32 EDT 2009

If you got a job flipping burgers at McDonalds, you could likely by the
converter and attenuator in less time than building them.

For the convertor put a WTB ad on Craigslist and save shipping. They are
commonly used for milling machines and lathes.

If you don't want to 'waste power', turn down the exciter and use less
attenuation.,

Your time, your choice.

-John

===========

> 	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?
>
> *********** REPLY SEPARATOR  ***********
>
> 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,
>>>
>>> *********** 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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>>>
>>
>>
>>
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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..."
>
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