IF, that capacitor were viewed as being directly across the primary of the coil that would be in a sense a parallel resonate circuit and that L/C circuit would do exactly what the problem that’s occurring is, sending the amplifier into oscillation. What do you have to have to make a oscillator? A resonate circuit and a feedback path, that’s why I am assuming that the B+ path is not conducting all the signal that’s there to ground and enough gets back in on the screen to send the tube into oscillation. Or perhaps the feedback is occurring somewhere else? From the resonate frequency being on the B+ or maybe B- bus, remember that everything is floating in that radio so in a sense its got many places to go wrong.

As far as tone control most tube radios did tone control at low level before the audio output tube because of all the issues that would occur if trying to do it at the plate potential, I will agree that it limits the high audio frequencies but still hold with it also killing short duration noise pulses, after all what’s the difference between high frequency audio and noise pulses? Besides duration.

Ray F/KA3EKH  

From: [email protected] <[email protected]> On Behalf Of Jim Whartenby via groups.io
Sent: Tuesday, May 3, 2022 1:20 PM
To: [email protected]; [email protected]
Subject: [MMRCG] Capacitor across AOT primary, was: RadioMarine Corporation AR-8506-B Receiver Resurrected.

No, the function of the capacitor across the audio output transformer is to attenuate the upper audio frequencies.  It operates along with the transformer's leakage inductance to act as a limiting tone control.  See Radiotron Designer's Handbook, 4th Ed, page 214, 4th paragraph.

Jim

Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy

-----Original Message-----
From: Ray Fantini <[email protected]>
To: [email protected] <[email protected]>; Joe Connor <[email protected]>; milsurplus@mailman <[email protected]>
Sent: Tue, May 3, 2022 10:12 am
Subject: Re: [Milsurplus] [MMRCG] RadioMarine Corporation AR-8506-B Receiver Resurrected.

Pure speculation, remember that I know nothing about ships but think the liberty ships used DC power system because if they did not have steam up and were not  underway they would run off the battery banks on board and when the boilers were up and running they would use the three fifty volt DC generators that were in series to keep the batteries charged and also maybe provide some form of regulation of the DC distribution system? Real simple system that works regardless of if the boilers were on line or not. The had oil lamps in the engine room so if there was no electrical power at all they would be able to get steam up and running the generators and get everything running that way. That ship although built during WW2 was all built around nineteen twenties technology.

If they had AC generators just imagine the problems of trying to sync them and transferring and always having to have at least one on line. With DC distribution you just fall back on batteries like in your car. Also with AC they would have to have at least two generators and there are no backup systems on a liberty ship, one engine, one shaft but they did have two boilers. Interesting footnote, the deck winches and all the machines on deck were all directly powered from steam and not electric. They have a huge diesel air compressor that you would see for being used for jack hammers and the like so that they can operate all the deck equipment without having to run the boilers.

Ray F/KA3EKH