[MRCA] Vintage test equipment?

[Ray Fantini]

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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