Last modified October 24, 2008
The R-270 is a BC-794 modified for dual diversity operation with an external master oscillator. Multiple R-270s, the master oscillator, and other equipment were part of the AN/FRR-12 diversity reception system. The old JANAP 161 says that the R-270's in the system are crystal controlled, probably with the MC-531 kit. The AN/FRR-12 system consisted of one six foot rack, two R-270s, and 2 RA-74-D power supplies.
The MC-531 was a add-on kit to add crystal controlled reception to the SP-2xx series receivers. Three switch selected crystals, and a crystal trimmer, were provided.
July 1960 QST, "Improved Selectivity for Older Receivers, A Low-Cost Half-Lattice Crystal Filter" by John M. Palmer, W1SGN. Uses surplus "numbered" crystals, fits in the original Lamb filter enclosure. Crystals 49, 50, 51, 52, 53 and 54, with labeled freqencies of 24.9 to 25.4 Mc, are used for the Super-Pro (465 KHz IF); crystals 41, 42, 43, 44, 45, 46 for the HQ-129X (450 KHz IF). Net result is a filter suitable for narrow AM or SSB at the expense of the narrowest CW bandwidth of the Lamb filter. Thanks to Alvin Bernard, NI4Q, for a copy of the article. My SP-210LX has this filter.
Jon Oldenburg, firstname.lastname@example.org, reports a SuperPro (no nameplate, SN #5243 stamped on chassis) with coverage from 0.1-0.2, 0.2-0.4, 1.25-2.5, and 2.5-5.0 MHz. This is unlike the SP-210LX/BC-779A which share the same two vlf/lf bands, but then cover 2.5-20 MHz in three additional bands. If you have any additional info on this model, please contact Jon.
Rich Post is currently restoring a R-129/U SP-200 variant. It covers 300 kHz to 10 MHz in 5 bands.
Jeff James, email@example.com, has a BC-779-A produced by Howard Radio. The radio, which served on USS Grafton, came complete with all original documentation in a ship's binder.
John Oldenburg, firstname.lastname@example.org, also has a Howard-produced BC-779A, serial 7469, contract #21109-phila-42.
AMR-200 by Eclipse Radio, Melbourne AU. (David Prince, email@example.com)
(Bill Sorsby and R.F. Buchanan). Several conversion/updating articles were in CQ Magazine:
Unknown mods performed by American Television Labs, Chicago, stated on front panel metal tag. (Charles Buttacavoli, LBFJ60A@prodigy.com)
Additional information may be found at Alan Klase's Super-Pro Data and Richard McClung's Cross Reference for Older Hammarlund Super Pro Receivers pages.
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