[Milsurplus] [MMRCG] RadioMarine Corporation AR-8506-B Receiver Resurrected.

[Ray Fantini]

Lot of weirdness and mystery, at least for me about how the whole DC distribution system worked aboard ship. Had the opportunity to crawl all around the SS John Brown and the original electrical system was 110 volt DC where they had three fifty volt DC steam powered generators in series and a massive battery bank that at one time powered the ships electrical system but think none of that's connected today and they are all 120 Volts AC from a huge Onan atop one of the holds.
Don't know how that relates to things like there gyro compass and displays being all that was up and running and if original would assume it's still DC powered.
Looking at that web site for that receiver can see where the B+ and B- are all isolated from ground so with that in mind there are plenty of places for feedback and osculation if everything is not right and also got to assume that over the radios lifetime someone has gotten into it and screwed with the wiring in a AC conversion.
When restoring one of those do you restore it to that point of working from the isolated DC source? And was there any reference to ships ground on DC distribution systems? Somewhere recall how on modern Navy ships the AC system is split in such a way that each leg is fifty or sixty volts relative to ground or something like that and not a hot and a neutral.

Ray F/KA3EKH


From: Joe Connor <joeconnor53 at yahoo.com>
Sent: Tuesday, May 3, 2022 9:58 AM
To: MMRCG at groups.io; milsurplus at mailman <milsurplus at mailman.qth.net>; Ray Fantini <RAFANTINI at salisbury.edu>
Subject: Re: [Milsurplus] [MMRCG] RadioMarine Corporation AR-8506-B Receiver Resurrected.


Ray, I've gone one on the bench now. I came across a pretty interesting website on these receivers.
http://www.wb6nvh.com/AR8506.htm<https://nam10.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.wb6nvh.com%2FAR8506.htm&data=05%7C01%7CRAFANTINI%40salisbury.edu%7Cc117868a6e764344e6a808da2d0cec95%7C2472f1faf24f421badd7b01c4b49be07%7C0%7C0%7C637871831226092992%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000%7C%7C%7C&sdata=fV%2BoEjyMkuS%2FBXqr2MZzKIQuLBdgMYUPSYdU%2FI3vALc%3D&reserved=0>

                 Joe Connor

On Tuesday, May 3, 2022, 09:48:39 AM EDT, Ray Fantini <rafantini at salisbury.edu<mailto:rafantini at salisbury.edu>> wrote:



Speculation, C-141 is there to bypass short duration pulse noise from the possibility of damaging the primary of the output transformer. They return it to G2 being that's elevated to B+ so you in theory would not need as high a voltage isolation capacitor if one end were grounded or perhaps they felt that by introducing an out of phase signal on the screen from the plate that would make the action of the limiter more effective? Cant see the entire schematic but would assume that if that radio is employing a common B+  bus and that the decoupling capacitor is keeping all signals off that bus. If its just a high value 4/8 uf electrolytic maybe it has a high ESR at the frequencies where the tube would tend to go into oscillation. Going to assume that there is also a couple small 0.1 or something like that scattered around the radio on the B+ bus for just that function. Also if C-140 were open that can cause weird things to happen. But I think the only way that stage can go into osculation is for there to be feedback from the B+ bus.



Did they isolate B- from ground? Also going to assume that's a radio that was powered by 110 volts DC? Somehow they had to develop a negative grid bias for the audio amplifier and would be curious how they do that? Don't know much about Liberty Ships but going to assume that one side of the electrical system was +110 /120 Volts DC and the other ground? So how would you go about isolating B-?



Ray F/KA3EKH




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