[MRCA] Vintage test equipment?

[J. Forster]

I strongly suspect that it was possible to fix and align an ARC-5 without
anything much more than a VOM.

I wish someone would take an unhacked set, check its alignment, swap in
the coils and IFTs from another aligned set, then re-test.

I expect that it would meet spec.

FWIW,

-John

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

> This all brings up a question in my mind of what was available and what
> the support structure was at the time. And what level of training,
> equipment and understand the maintenance technicians had.
> I am assuming that operational level maintenance was mostly setting radios
> on frequency during preflight and replacement of radios outright, Field
> level maintenance would include simple things like tube and dynamotor
> replacement or other minor repairs and not require much in the way of test
> equipment and Depot level is where any complex repairs or modifications
> were performed.
> For operational level the only thing required is a frequency meter like
> the BC-221, that’s why so many were produced. Field level would require
> a VOM, tube tester and any test sets used with the radios but would not
> think IF or front end alignment was in there normal scope of work, and if
> they were to do alignments I would assume that they would not be beyond
> the common practice of fixed injection of the IF with a modulated 400
> cycle signal and using the old and trusted “Tune to Max” procedure
> with a meter across the audio output. Depot level is where calibrated and
> complex test equipment would be located but it’s also important to
> remember that with the requirements of production facilities and there
> need for calibrated references how much would be available for Depot level
> use? And with the massive amount of production was depot level maintenance
> viable? Instead of spending time repairing serious issues with a radio
> just outright replace it with a new one? Today DRMO is flooded with an
> almost endless supply of generators that were sent back for depot overhaul
> but are being sold surpluses instead. Perhaps the depot system only
> addresses a fraction of what’s sent it?
> Ray F
>
> From: mrca-bounces at mailman.qth.net [mailto:mrca-bounces at mailman.qth.net]
> On Behalf Of D. Platt
> Sent: Thursday, April 10, 2014 10:10 AM
> To: Military Radio Collectors Association; ARC5 at mailman.QTH.net
> Subject: [MRCA] Vintage test equipment?
>
> In reviewing the alignment procedures and maintenance practices, etc. for
> the SCR-274-N and ARC-5 equipment, I'm curious what test equipment they
> (the military) had at the time and, in fact, used for the aforementioned?
> I know that the early scopes were present, although not "calibrated" as we
> know it today.  I also know the BC-221 and LM were readily available, of
> course.  Also, fairly accurate voltage measuring equipment, to include, I
> believe, VTVMs (which would provide high impedance measurements).  I
> suppose that the standard 20k/v multimeters would obviously have been
> available.  Finally, signal generators, too.  The thing is, accuracy and
> precision is my real question.  I don't think that the military had quite
> the PMEL functions available today.  How good were the test sets out in
> the field?  Boiling it all down, I read the procedure in the maintenance
> manuals for the above radio sets, in particular the receivers and their
> alignment and test.  If I'm interpreting things correctly, the procedure
> for measuring receiver bandwidth was one where, instead of setting up a
> reference on the desired frequency and moving a calibrated signal
> generator up and down or sweeping the bandpass, they (Navy and Army) used
> a method whereby the signal generator was set on frequency and the
> receiver was tuned above and below the set frequency (or was it the
> reverse?)  Anyway, by increasing the signal generator levels in discrete
> steps up to values representing from 6db (2x) to +60db (1000x) from the
> reference, the receiver (or generator?) was off-tuned until receiver
> output was seen to drop to the original set level.  Of course, the method
> does work, no question, and by using fairly accurate (and measurable at
> the time) high levels, the results could be considered good.
>
> Does this seem reasonable to all of you?  Again, other then the LM and the
> BC-221, what other "standard" RF and measurement test gear was in use from
> '42 thru '45?
>
> Inquiring minds ask.......
>
> Jeep K3HVG
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