Yes, a tube can be bad even with the filament glowing. The filament is used to heat a metal (usually thorium) that emits electrons, and with age the number of electrons emitted by the tube declines, in which case the tube is termed to be "weak" and is replaced. That's why tubes get replaced. In addition, there are many capacitors in the radio which gradually fail with age, so even if all you tubes are okay those caps can be the major cause of the radio's poor or non-existent operation. Less likely a cause is burned out resistors, which you should also look for, primarily with a visual inspection but also, when you have time to dig into things, with a resistance check on each one. To do a decent job on a receiver you need a signal generator that you use to inject RF signals at different points in the receiver's circuitry, and doing that will enable you to isolate electronic receiver sections that are not working or are otherwise out of spec.This is odd...
I decided to remove both side panels and pulled out every tube to see if any were burnt out (I didn't see any). I put them back in, reassembled the radio, and turned it back on. Lo and behold, there was a burst of static every time I touched the antenna. Now, I notice that the static tone and pitch change every time I change the MHz band. Unfortunately, I have yet to hear a single voice.
Also, during my inspection, I discovered that all of the tubes were from different manufacturers, so at some point someone had replaced the original ones.
Think of it this way. It's 40 years old! One ... it's gonna need some TLC. Two ... it's no where as complicated as a current computer.This is rapidly getting above my level of expertise, considering that I am new to the world of vacuum-tube electronics.
There is no difference between 24 volts and 28 volts, at least where this receiver is concerned. Most Army/Navy electronics used in vehicles ran on the vehicle's electrical system which was 24 volts. They used 2 standard 12 volt batteries in series. The 28 volts listed is for a vehicle electrical system that is being charged. Your car's 12 volt battery will measure 14 volts with the engine running.I just thought of something. Depending on which specification I look at, it says the power input is either 24 or 28 volts. Even the manuals seem a little ambiguous as to what the voltage input is, with some pages saying 24 volts and others saying 28. Should it be 28? It just occurred to me because I noticed that my 24 VDC 6.5 amp power supply got very hot when I had the radio on. Although this might have something to do with the problem, in my world, the simplest solution is usually NEVER the actual solution. :roll:
Your own listing of the nameplate data doesn't reference that your R-392 was built by Collin but by some other manufacturer. For military surplus collectors the value is usually much higher for genuine Collins made receivers.Has anyone ever played around with one of these? I just got one yesterday, and would be interested as to what people think of this.
I did. None of the symptoms match what my problem is, which is simply no RX. I was playing around with the tubes when I nudged one (I was doing it with the power on). The static went away and the audio almost completely faded out. I noticed that this happened only when I pushed the metal shield covering it down some. The tube socket is marked "V506" which is listed in the schematics as the "6th IF Stage". I noticed something similar with the Calibrator-Oscilator Subchassis. When I nudged the V701 Multivibrator tube, there was a pop of static. However, when I removed the V703 Harmonic Amplifier and Distorter tube, there was no effect on the static.Check that site. It had some component numbers that often go bad along with symptoms.