[R-390] Help needed for two R-392s

[David Olean]

thanks for the long and thoughtful note, Roger,

Well I know I can get all three receivers working. Fortunately, only one 
tuning rack is missing and I have located another RF deck (on EBay) for 
the R-392 thanks to this list! With this parts source, I can get the two 
RXs working.  The EBay RF deck has the rack and slugs for 3-2, and I am 
sure I can match some other slugs with similar permeability that are 
already in the RF deck. The low frequency RF banks are probably the same 
mix or close enough to work as you described. When this is all done, I 
will have plenty of slugs, coils racks and cams available for others 
should more missing parts show up on the list!  The 3-2  Mc variable IF 
rack is unusual as it is two rows of coils in tandem to fit in the 
available space, so it is a "mongrel" unlike any others in the 390 
series or in other portions of the R-392. I figured that if worse came 
to worse, I could fabricate my own slug rack. I have an engine lathe and 
a non Bridgeport milling machine. I have made parts before for other 
repairs. Fortunately this RF deck should solve my problem.

When I was in the Signal Corps during the Vietnam War, my signal 
battalion had R-390As as well as the R-392s. (AN/GRC-26D used two 
R-390As while the AN/GRC-19 used a T-195 and the R-392 for the 
receiver.)  For a significant length of time, I was the battalion S-4 
and signal maintenance officer and I was directly involved with all the 
gear making sure it got fixed. The 390s and 392s hardly ever needed 
work. What I found was that the higher echelons of maintenance (3rd) did 
a fairly lousy job for us. As a result, our work involved repairs that 
were really out of our bailiwick, but we did them out of necessity.

So here I am 50 years later and I am working on R-390s and R-392s again. 
It feels funny but good!

I was not aware that bands were disabled on some radios. A few of my ham 
friends had mil careers as intercept operators overseas. All of them 
spent time listening to USA AM BC stations when the NCO was not 
looking.  In Europe, WKBW in Buffalo and WBZ in Boston were favorites. 
They played rock and roll music back in the day. Creedence Clearwater 
Revival sure beat 5 letter code groups. The rhombics picked them up 
pretty well. Disabling coil sets would definitely curb that activity.

I have one R-392 already working just great with super sensitivity on 
all the bands. The AM BC band is especially hot. Receiver #2 has three 
missing slugs in the 2nd variable IF at 3-2 MHz.  I can tell the 
receiver will work because a strong signal will still get through that 
variable IF without the slugs. It picks up all the bands, but needs a 
loud signal to get through.  I could even check the PTO end point just 
by picking up the signal generator across the band. It is off about 6 
kHz.  Receiver #3 does not work, but the IF strip works fine. I must be 
missing an oscillator or have a bad tube, but it sure looks like nothing 
much is wrong. It draws the correct current,  A few minutes with a scope 
and I should figure out what is missing.  I'll bet it is the crystal bank.

Thanks for all the help.

Dave K1WHS


On 12/15/2019 9:46 PM, Roger Ruszkowski wrote:

> Dave, Welcome to the R390 group. No one has a model that covers cost and has a return thatexceeds the aggravation on the investment. We are luckyany thing is on ebay. Those of us who have stuff know whereto find and read our sales leads.  We hope to collectively keep a large enough stall open that serves a niche in the online marketfor the Amateur Radio Community. Please ask here for parts and the text is free.  Ask for troubleshooting help and receive awesome knowledgeable help for manyexperienced Amateurs who share a hobby interest or better with you.  Needed for an R392 are two sets of slugs, one 3-2 MHz rack and the two springs that guide the rack on the cams. The exchange of parts happens one on one and we will not seethe offers and the deals you make for parts. The transactionsin front of everyone has no reading value. I do not know the R392 as it was a field radio not used in my units. Dave you may have parts in hand to put two of the three back into full operation.Six slugs two springs and a rack gives receiver three a full chance. The springs are common and those are topics in the R390 pearls of wisdom.I do not know that the  3-2 MHz rack is unique. The same rackmay be used in other octaves. The R390 and R390/A use a left and rightrack part a or part b. You may be able to swap a rack from another octave.like 8-16. The slugs may be the same as the 0-2 or 4-8 slugs. Looking at the racks you will see if another rack will work.The parts manual will help you locate the slugs in the receiverthat are the same. You may have parts in hand and just do not know it yet.Both the R390 and R390/A only used two types of slugs in the RF deckand a third type in the variable IF tuning sections. If the slugs will fit the 4-8 slugs will almost peak well in 2-4.Thus some part of the octave will be good and the other end not so good.But the receiver is not chopped up and operates. The exact value of the core slug is not critical.We would like the core material to exhibit the same flux value across its intended range of operation. Any slug in the receiver meets these property requirements. The cam holds a mass in an RF field. As long as the cam holds the same mass with the sameflux at the correct distance within the field the distance can be set and the mechanism will tune and track as well as the coil winding allows. The change in core material is to coverthe operating span with a linear core material. The goal is a flat response transformer.No one core mix is equal across 32 Mhz. As long as more than one material mix is neededpick the best divisions and mixes for the divisions. Part redundancy and minimum partswere design requirements. We know the R392 slugs are unique mechanical sizes. We need to get you into theR392 parts manual where you will find a part number for the slugs and all the otherplaces in the receiver where the same part number is used. Time, color, paint dots, springs, spline size, and glue have all changed, but the tuning slugparts are identical in fit and function and work as required by design specifications. Wehave learned you can not look at a part and know if it swaps. A lot more parts are the samethan look the same, but you need a program to follow the game. Get a slug loose on the bench and no one remembers where it came from and theyalmost never get recovered and returned to service. History is parts and like a parts manual each part has an index part number, noun name nomenclature,item description and reference to all location where the part is included in the units design. Any NATO part in the 5960 part number system has a vacuum. Vacuum management is required for a part to be properly indexed into the 5960 class. Over seas the missing octave is AM long wave broad cast around the Amateur 3.5 to 4 Mhz 80 meter band.Allocated military does not include this range of operation. The slug were pulled to keep the local nationalsfrom using their U.S. Military resources to listen to the radio while on duty. A common but notdocumented operating procedure in some units. As you switched the Mega hertz the local broad cast stationdid not knock the cans off your ears every time you crossed the mega hertz no matter what the kilo hertzVFO was indicating. The band was broadcast noise and disabled for local operating convenience.A jail house window screen and an R-390 had been used to log WBZ Boston was at over 200 mixed frequencies at Fort Devens Mass. about 50 miles from AM broadcast tower tothe window screen on the second floor. It was a class room demonstration of the receiverssensitivity. Name the frequency and look up the station that is mixing with WBZ Boston on arusty fence post some place and being received quite clearly on the receiver.  Students training to fox hunt enemy transmitters, were given jeep units and did field exercises looking for the source of the mixed and reradiated energy. The students drove all over the area and found every daymechanical structures were solid state oxide diode mixers with some what tuned antenna lengths. It was common to disable a band on receivers. Keep asking for parts with a paragraph until you havethe parts you need. The parts are not free. Many of the Fellows who have a hanger queen and areparting it out do not read every mail and miss requests. Fellows,  Does the R392 have a reflector page like the R390 page?Does the R392 have a document web site like the R390.net page? The R392 owners need to be populating the R392 page with copies of the military manuals including the parts manuals. The R389's would like equal consideration. Respectfully, Roger Ruszkowski AI4NI

>    -----Original Message-----
> From: David Olean <k1whs at metrocast.net>
> To: R-390 Forum <r-390 at mailman.qth.net>
> Sent: Fri, Dec 13, 2019 9:29 pm
> Subject: [R-390] Help needed for two R-392s
>
> I purchased three R-392 receivers at auction.....