[HBR] LWM-3

[john]

Walt, I'm really glad this got to you, and I hope we can read about it's 
revival either here or in ER. I'm sure Kees was glad to see it go to a 
good home as well.
73
John K5MO

On 4/7/2016 6:37 PM, Walt Hutchens wrote:
> Kees said:
>
>> The unit was built by a Dallas ham who had access to a large USAF
>> electronics dump while in the service and those PTO's are out of
>> some period bomber which he found. He was going to use one in the
>> Transceiver and the other two are spares. They are all Collins, of
>> course. What parts are missing I don't know. It will be a labor of
>> love to bring it to life, but what a rare piece of homebrewing history.
>
> I have Kees' LWM-3 in house now, and what a beautiful piece of work it
> is. It's probably 80% finished and the workmanship is about 3.9 on a
> 4.0 scale.
>
> It appears completely wired except with regard to the non-installed
> linear oscillator, missing mechanical filter, and minor odds and ends.
>
> I have what is probably a suitable mechanical filter: It's one of the
> small ones from an SB-34 transceiver: Intended for use with
> transistors but I think I can fudge that.
>
> The PTO's that came with are Collins 70H-13 units from the ARC-58
> transceiver.  They tune 2-4 Mcs in 10 revolutions while the LWM-3
> wants a range of 200 kcs that's within that range -- I don't have the
> numbers in front of me right now.  So that could be fudged by using
> just one revolution or by changing the tuning range -- not as brutal
> an operation as it might seem.
>
> Because the PTO drive should be direct (for zero backlash) and 20
> kcs/knob revolution is about right for SSB I lean toward changing the
> tuning range. Add a coil in parallel and another in series with the
> existing coil, just as when padding a tuning cap to a desired range.
>
> There's a knob and shaft to tune the PTO on the panel but no gearing
> or other mechanism. There's a mechanism for the permeability tuned RF
> amp/driver but it does not work well and will likely be replaced: I
> can either use a modern belt drive -- that stuff is excellent and
> reasonable in price now due to computer printers and other office
> machines -- or substitute a permeability tuning assembly from a scrap
> FT-101. I lean toward the latter since the Q of those coils is
> outstanding.
>
> It needs a power supply but that's not complicated -- I have a KWM-2
> p/s that probably would do it for starters. The connectors on the
> LWM-3 are the same as for the KWM-2 so at worst I might have to change
> a few connections on the LWM-3 receptacle and do something about a
> lower plate voltage for the PTO (two 5749 subminiature pentodes) if
> the KWM-2 p/s doesn't provide.
>
> None of the crystals are there but that's a solvable problem.  No top
> or bottom metalwork -- another small project AND far in the future.
>
> Some tubes are there, some are missing -- I probably have what's
> needed. Usually when doing a project like this you find more as you go
> but this has the look of being at least partly checked out.
>
> This will be a winter project: I have far too much outdoor work to get
> done to tackle anything substantial right now. However, I'll start now
> on the PTO re-tuning and drive. The KWM-2 dial drive was designed for
> low cost but beginning where this rig is I can probably go first
> class.
>
> The original LWM-3 uses a command transmitter tuning cap so that's not
> applicable. The chassis in this unit was cut for the PTO and there.s
> not room for the tuning cap. I'll try to drive the PTO directly from
> the knob and use a toothed belt drive for the dial: 10:1 reduction
> with the PTO retuned to cover just over 200 kcs.
>
> One of the three PTOs has a badly bent shaft -- no surprise since AF
> scrap yards typically get gear removed from busted up airplanes. I
> will start with that one, see if I can get it working, and then tackle
> the retuning and mechanical drive issues.
>
> I'll hope that by winter the obvious separate projects -- PTO,
> mechanical filter, power supply, tubes, crystals, etc. -- are done so
> I can move on to getting it to work at the point where I can start to
> concentrate more.
>
> You cannot believe the nice workmanship. The constructor made
> fiberglass-epoxy terminal boards and much of the wiring is on them.
> The point-to-point components and cabling are professional grade, the
> wire is Teflon insulated. The relays are military sealed units,
> ditto the audio output transformer. Assembly is with 4-40 machine
> screws tapped into aluminum plates that were home cut/bent but very
> nicely -- nothing beat up with a hammer to make it work. The rear
> panel was taken from a piece of Collins gear complete with the Collins
> logo decal on it.
>
> Thanks again, Kees!
>
> Walt
> KJ4KV
>
> ______________________________________________________________
> HBR mailing list
> Home: http://mailman.qth.net/mailman/listinfo/hbr
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:HBR at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

-- 
III