[AMRadio] elderly bc gear

[Nigel Holmes]

"...not uncommon to find a new transmitter in the same building as 40 or 50 year old units that are still operational."

RA's first tx at Shepparton was an RCA 50MF cost: US$87,395.25 in 1943. Fired its first salvo on 4 May 1944 on 15 Mc (& heard by Gen. McArthur near the Philippines). Still scheduled in 1998 when replaced with a 1974 vintage Gates SW100... The antenna was "J15" (J=Japan) a single-band, 16 dipole array with tuned reflector which remains in daily service. The wire elements are "600lb hard drawn copper".

The 50MF was equipped with the optional keyer intended for high speed telegraphy. It was pulsed on > 20 Mc for moon-bounce experiments in the late 40's/50's using the "American Rhombic" on ~ 065 deg. The rx was in another state ~ 1000 km distant.

I can't recall if the RCA ever experienced an MBL-100 - if it did then it would have been applied gently in deference to the iron & 880's

73 Nigel VK3DZ


-----Original Message-----
From: On Behalf Of W2XJ
Sent: Wednesday, 15 June 2011 6:32 AM
To: Discussion of AM Radio in the Amateur Service
Subject: Re: [AMRadio] Broadcast Processors

The MBL 100 had compensation to handle a less than perfect low end. The first transmitters where it was ever used were 500 KW  PDM units, 250 kilowatt plate mod shortwave transmitters and a 625 KW PDM MW TX. The PDM units had a design issue where the power supply choke was resonant somewhere in the 30 hertz range and if you hit the resonance there were fireworks so low end protection was necessary. Ultimately that problem was solved by removing the choke  and re-working the PS filtering since the PS was 12 pulse and the choke was not really necessary.  The plate mod shortwave TX was what it was. There were a lot of high power transmitters in the field that could not meet the ideal near DC low end response as the organizations that typically used high power TXs tended to accumulate transmitters. It is not uncommon to find a new transmitter in the same building as 40 or 50 year old units that are still operational.


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