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R-390a Strange Issue

Discussion in '"Boat Anchor" & Classic Equipment' started by W2WDX, Jul 5, 2018.

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  1. W2WDX

    W2WDX Ham Member QRZ Page

    Hi all,

    I finally got my old R-390A out of storage and set it up for the first time in several years. However, I connected the balanced antenna connection as I always have and I'm getting no signal. I'm getting noise, but it's as if the antenna line is not getting into the RF section. I did the usual things like check tubes, and continuity of the cables, as well as tested the antenna relay, which are all fine. Everything works normally, but the antenna signal is simply not getting into the RF unit.

    I haven't tried the unbalanced antenna jack yet. I know my way around R-390a's well, but this one has me miffed. Here's the odd thing. When I tune to a strong local broadcast station frequency (880 in NYC) and place my finger on the antenna trim gear, the station then comes in fine. Could it be one of the bypass caps to ground off the trim circuit maybe (C22 in the RF amp?)? I hate the idea of pulling out the RF unit.
     
  2. KC8VWM

    KC8VWM Moderator Volunteer Moderator QRZ Page

    Sometimes the coax cables connecting to the IF module on the R390A is the culprit. I had a similar issue with "weak signals" and after disconnecting them and cleaning them up a little, it restored the signals.

    Try the unbalanced antenna jack anyways.

    Another issue I ran into is tube pins not making proper contact in the sockets on the IF module. I learned this when tapping them with a chopstick. So after pulling them, cleaning up the tube pins and reseating them back in the sockets again, things started to come alive again.

    Another thing that kills signals off is the tube installed in the PTO. What usually occurs is there's signals on one potion of the band, but not on others, so try tuning the entire range of the tuning dial to see if anything changes.

    However, sounds like the radio just sat a while resulting in a poor electrical connection issue somewhere. Most likely resides within the IF module. Crystals "could" be the issue for lack of signals, but not likely all of them at the same time. Try working the bandswitch knob too, it may be dirty.

    Caps gone awry could be another issue and it's not a bad idea to change out the caps anyways, but try these other things first.
     
    Last edited: Jul 5, 2018
    KC8YLT likes this.
  3. W2WDX

    W2WDX Ham Member QRZ Page

    Yeah that's the thing. Everything works fine on every megahertz selection if I put my finger on the antenna trim gear. It's not mechanical, it's some type of capacitance loading to my body, since it only takes the slightest touch; I'm not wiggling the gear or the cap underneath at all. So that means everything after the first RF amp is working fine.

    Here's another thing, since I finally cracked open the filter case for the first time ever (Yeah I know ... they worked so I never looked). And yes ... the killer cap was fixed a long time ago, along with a complete rebuild and mods. I have replaced the "line" section output transformers with hi-fi types and changed some values on caps in the audio amps, so the line output section sounds even better than the diode out everyone else uses. This thing sound more like or better than a R-390(non-A) on the line outputs. I did this so I can use the meter on the radio to make sure I'm not overloading my audio amplifier.

    So anyway ... What the heck is this? The little cans have what appears to be slug tuning, but no coils. Obviously, this is some aftermarket filter ... I'm just not familiar with it. Anybody know?

    What_is_That.JPG

    At least now I can put in the IERC tube shields I got for this a while back. I hope I don't have to pull the RF section. Grrr ...

    Incidentally, I just picked up another R-390a which appears to be from the same person in California I bought this one from a few years ago. An engineer from the JPL. It least it has the same mods and labels on the front panel. I noticed the front panel labeling (and other internal work) showing the mods for the audio section response additions (CW-Sharp-Wide-Flat), so I guessed it was the same JPL guy's other radio. Everybody has there own "signature" style of making mods, so I picked this up (maybe for too much) on the off chance it was the same guy; since I know these mods and the quality of work performed by this individual. Real lucky find.
     
    Last edited: Jul 5, 2018
  4. W2WDX

    W2WDX Ham Member QRZ Page

    I just looked. The new radio has the same filter mod and the same external case, so it must be from the same guy. The work, at least quickly "looking under the hood", appears to be identical.

    Hmm ... should I try diversity? Hmm ...
     
  5. W5INC

    W5INC Ham Member QRZ Page

    Do the non factory mods improve the performance of the rig? If the mods do indeed improve the performance of the radio and the workmanship incorporating those mods is top notch, why would you need diversity? Some purists hate anything that isn't just as it came out of the factory in a rig. IMO, if some mods can be made to a 60+ year old radio design to make it preform better in today's real World, go for it. Since you have already improved upon the 390's factory audio amps Mr. John, I'm guessing you aren't a "true" purist to begin with. :)
     
    KC8YLT likes this.
  6. W2WDX

    W2WDX Ham Member QRZ Page

    No ... I am not a purist. I'm a pragmatist. While I do like restoring vintage gear (and I do many times restore to factory fresh, especially if the piece is historically significant), for gear I use everyday I will go ahead and try to improve performance. My use of digital audio processing in a dual Xeon workstation, instead of using something like a an analog Optimod on AM, for instance. If it performs better and doesn't take away from the benefits (or appearance) that makes an R-390A special, I will take advantage of it.

    Diversity
    is used with R-390A's in two types for reasons not related to receiver performance. To reduce fade (Dual Space Diversity) or to reduce phase distortion (Polar Diversity); both due to atmospherics. To have better performance in the radio only improves performance internally; it does not help correct these localized atmospheric phenomenon. Of course this all only applies to AM reception.

    I most likely will try Polar Diversity since I do not have the physical space for two dipoles spaced at a wavelength apart needed for a Dual Space system. However, I can use a vertical and a horizontal for Polar Diversity, thereby reducing phase distortion due to wave rotation which I do get here.
     
    Last edited: Jul 5, 2018
  7. W5INC

    W5INC Ham Member QRZ Page

    You AM Babylonians do seem to have that problem for some reason. :D
     
  8. W2WDX

    W2WDX Ham Member QRZ Page

    Babylonians?! ... may I remind you sir, we are probably the only Hams left who actually design & build our own gear. I'm not just talking tubes & iron; modern class-E, D MOSFET transmitters and SDR receivers, as two examples. Some design and build VoIP based remote capability with custom software as well. And our duty cycle forces us to build real tuners and amplifiers; not the turn-key auto-tune weakly-supplied nonsense most instant-gratification Hams seems to spend money on these days. :D

    Not me mind you ... I'm a boatanchor lover. Hihi!
     
    KC8YLT and AD5HR like this.
  9. W5INC

    W5INC Ham Member QRZ Page

    Is Lindenhurst still in the Town of Babylon, NY? :D
     
  10. W2WDX

    W2WDX Ham Member QRZ Page

    Oh ... umm ... yikes. Thought you meant "ancient peoples", not peoples from Babylon. Umm ... D'OH !!!

    o_O
     

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