[Milsurplus] R390

[Mike Morrow]

The easiest and most obvious way to distinguish between models without nomenclature plate is to examine the FUNCTION switch on the front panel.  The R-390/URR has a SQUELCH position...the R-390A/URR does not.

The military found the original R-390 to be unproductively complex and a maintenance burden in addition to its expense.  That is why the R-390A was produced far longer in far greater numbers than the R-390.  For that reason alone, you most likely have an R-390A.

AM-using hams seem to prefer the audio bandpass of the R-390 LC filters over that of the R-390A mechanical filters.  The military clearly considered the R-390A to be the better equipment for their needs.  I agree, but have no noteworthy credentials.  Although R-390A receivers were used on board US nuclear submarines, the R-1051*/URR had replaced them years before I got to SSBN-629.

At my age and health status, I never intended to buy one of these 80-lbm monsters.  However, I found an R-390A in very good condition, guaranteed working and complete, including the typically missing top and bottom covers and associated screws.  It's a 1958 Mororola set, order 14385-PC-58.  Because it was complete, I could not resist its $150 price (lowered from the start of the hamfest $250 price, and from its month-earlier $450 price), especially when the seller lent me his hand truck to get it to my truck.

I had good luck the last two hamfests I attended before the scamdemic.  At the last I bought a R-26/ARC-5 that I did not need for $15 because it came with SCR-274-N local control adapter panel FT-260-A and tuning knob A.R.C. 6749, both in new condition.

I miss the local hamfests.

Mike / KK5F

-----Original Message-----
>From: Gordon Smith <gfsmith at cox.net>
>Sent: Aug 23, 2020 11:20 AM
>To: mike christie <MZFB at aol.com>, Milsurplus at mailman.qth.net
>Subject: Re: [Milsurplus] R390
>
>HI Mike,
>Here is a basic discussion on the differences between the "A" and 
>"Non A":  "The R-390A was a cost reduced R-390. To do this, they 
>reduced tube count from 32 down to 26. One stage of RF and 4 stages 
>of IF, rather than 2 stages of RF and 6 stages of IF. Also, the "A" 
>has a simpler, more conventional power supply without the regulator 
>tubes.<P>The biggest difference is that the "A" has, with very, very 
>few exceptions, mechanical filters."
>
>Discussion can be found here: 
>https://www.antiqueradios.com/forums/viewtopic.php?t=5427
>
>So you should be able to find out quickly what version yours is
>
>73, Gordon KJ6IKT
>
>
>At 08:55 AM 8/23/2020, mike christie via Milsurplus wrote:
>>Content-Type: multipart/alternative;
>>         boundary="----=_NextPart_000_0002_01D67944.41CBA350"
>>Content-Language: en-us
>>
>>I've  inherited  an R390 it doesn't have a data plate on it so I 
>>can't tell if it's A or not.  I have it up and running but the 
>>sensitivity is really bad on all bands.  I can hear WWV on 10 and 15 
>>Mhz but not really strong and I went to the Amateur bands and I 
>>could hardly hear anything there either.  All the controls are 
>>working such as the BFO, limiter, Broad & Sharp,  RF gain etc.  All 
>>the tubes are lit and I am getting background  noise. I've switched 
>>between antenna inputs and I get the same results.  When I'm tuned 
>>to WWV the Dial is correct for at least on  10 & 15 MHZ. Also I can 
>>hear when the antenna is plug in also.  So since I'm getting back 
>>ground noise on all bands,  I'm thinking I've got some bad tubes at 
>>least on the front end.    I've used one when I was I in USMC so I 
>>know what their capable of.
>>Can some give me some pointers as to what maybe the problem?
>>Thanks
>>Mike
>>W1ZFB