These pages are devoted to the Radiomarine Receiver Model CRM-R6A.  This 16 tube classic saw service ashore at RCA coast stations and afloat in Radiomarine consoles from the 3U (as a retrofit) to the 6U and beyond.  As far as I know this was the last receiver produced by Radiomarine.  Its sister receiver, the AR-8516, was available for AC/DC use aboard ship.

The CRM-R6A covers 80kc to 30Mc in 18 bands.  Thus it covers all the CW bands in the Maritime Mobile service including the LF and MF as well as HF frequency bands.

The receiver uses double conversion for band 1 (80 - 200kc) and band 2 (200 - 520kc).  On band 3 (520 - 1300kc), band 4 (1200 - 3000kc) and band 5 (2 - 4Mc) the receiver uses single conversion.  For the remaining bands the receiver uses double conversion.  The IF frequencies are 825kc and 455kc.

MRHS member Richard Dillman was lucky enough to add an example of this classic receiver to his collection.  Here's his report.


Unlike most items of classic communications gear the provenance of this CRM-R6A is known. It was owned by a manager at Radiomarine Corporation in New Jersey who is now sadly deceased. The person who sold the receiver to me, a friend of the original owner who helped settle his estate, was kind enough to provide the following information:

RD- The former owner of the radio was Gordon C. Hopkins. He was born in 1915 and died on March 7, 2003. He worked for RCA/RMCA for many years. If you would like the specific years, I could ask his daughters. I do know, however, that he published an article in "Marine Technology" in the October, 1968 edition. This publication was published quarterly by the Society of Naval Architects and Marine Engineers. The article is titled "Modern Trends in Ships' Radio Communications. The article indicates that he was Manager of Ship System Sales, RCA, Radio Marine Products Department, Camden, NJ. I will include this publication when the radio is shipped or picked up.

I knew him personally to be a very fine gentleman and I often stated that he was definitely the nicest man I ever knew. As an aside, he was my 90 year old mother-in-law's "boyfriend" so he was considered part of our family since the early 90's.

He shared some stories of early working life which included that he installed radio antennae on 400 foot towers in Buffalo, NY, in 1941. During the WWII, he had clearance to go on any ship in New York harbor although I am not sure in what capacity.

I have always felt that when one acquires a historically significant item of communications equipment a certain responsibility comes with the acquisition. That responsibility includes the preservation and protection of the equipment so it can be enjoyed and studied by future generations. In the case of this particular receiver the responsibility goes deeper because the former owner is known. In this case not only will the receiver be preserved but in doing so the memory of a fine man will be preserved as well. Thank you, Mr. Hopkins, for taking such good care of this wonderful receiver.


Another proud CRM-R6A owner has written after seeing Richard's receiver on the Web site.  In his movong note below Paul M. Brady tells how a single receiver can inspire a career.


I just stumbled on your website about the CRM-r6A receiver. I thought I was the only one out there that even knows that they exist!

I bought my RCA in June of 1993, complete with manual. I went down to the Dallas Ham Fest looking for a shortwave radio with a BFO. Up to this point I'd been using a modified home stereo to listen to shortwave (a coil of wire wrapped around the antenna coil of the AM receiver) that did nothing but drift even if you looked at it the wrong way. I found it sitting under a guy's table. I was 19 years old at the time and I hauled this heavy monster home in the trunk of my 1966 Mustang. Mom flipped out when she saw it, thinking it was going to burn the house down. I plugged the thing in, made an antenna out of clip leads, plugged in the head phones and was blown away by it's performance. The amount of stations I've heard using this radio is unbelievable. I've heard pirate stations, ship to shore communications, spy stations, military communications and all of the international broadcasts I could ever want. I had this radio sitting by my bed on my desk and I used to lay awake at night listening to hams rag chew on 80 meters. This radio never, ever drifted. It was truly a 'set-and-forget' radio.

To put it simply, this radio opened up a world that I never knew existed.  Quite frankly it's directly responsible for me getting my ham license in 1994 and my electronics degree in 1998. It started my addiction to boatanchors ;) I will never part with this radio.

I have taken great care of this rig over the years. I pull it down every year and do basic maintenance as recommended by the manual. Right now I'm in the process of doing a full alignment on it.

Thanks for shedding some light on these truly fantastic radios!

Paul M. Brady


View all images as a slideshow

Paul Brady's CRM-R6A undergoing alignment as he mentions in his note.

... the inventory tag with the receiver.

The list of tubes and their application shows that the CRM-R6A uses some tubes not usually found in communications receivers.  In my receiver the 6CU5 audio output tube runs very hot.  Other owners have reported that theirs also run at a high temperature.

Richard Dillman writes: I was lucky enough to get the manual, and...

The power transformer appears small - and is, compared to the transformer in a SP-600 - but it runs cool to the touch. The four section variable condenser to the right is associated with the sector control.

Two 9 pin sockets are provided for 1.5kc and 0.5kc mechanical filters available as accessories. It appears that the accessory filters may have the same form factor as those used in the Collins 75A-4.

The below chassis view shows a clean, neat layout.

The next step was to remove the knobs to clean them and the front panel.

I separated the receiver from the case to make it more manageable for carrying to my second floor apartment. With the case it weighs 92lbs. The receiver alone weighs 67lbs. Here it is being brought up for the first time on a "Variac" (actually an Adjust-A-Volt). The receiver uses solid state rectifiers. As the lamps and tubes began to glow and no signs of smoke appeared I began to think I had a real winner on my hands.

With the connection of a speaker and an antenna the CRM-R6A began receiving signals for the first time in who knows how many years.

The speaker shown above is a Radiomarine LS-1. It is in a wooden box with a metal front plate. The switch is used to select between low and high impedance. Even though it is not the correct speaker for the receiver it makes a nice match and will do until the correct speaker, model RM-290, can be located. If you are willing to part with a RM-290 please contact me immediately!

Directly above the band switch is an illuminated indicator showing the correct sector control position for the selected band. To make sure the operator selects the correct sector control position the dial lights are interlocked with the band switch and the sector control. The dial lights only light when the correct sector control position is selected!

Shall we finally talk about sector control? To paraphrase Casper Gutman's reply to Sam Spade, "Let us talk about the sector control by all means, sir." As we have seen in the block diagram presented earlier the sector control tunes four stages of the receiver (thus the four sections in the sector control variable condenser). These are the RF amplifier for bands 6 through 18, the first mixer, the RF amplifier for bands 1 through 5 or the IF amplifier for bands 6 through 18 (the same stage, V104) and the second mixer.

Note in the photo above that there is an arc or sector beneath each of the four detent positions of the sector control. That's because the pointer on the sector control knob may lie anywhere within that arc or sector depending on the band selected and on the portion of that band that's being tuned. In other words the sector control tracks the band and tuning point of the receiver through a mechanical linkage.

There are several options for selectivity in the CRM-R6A as normally supplied from the factory and two additional selectivity options offered as accessories. In the standard receiver IF selectivity settings of 6kc and 3kc (at 6db) are available. Two cascaded overcoupled transformers are used for 6kc selectivity. A Collins mechanical filter with the same form factor as the filter used in the R-390A is used for 3kc selectivity. AF selectivity is provided via a 0.1kc audio filter.

The BFO has a calibrated planetary drive for setting the offset. The index knob is used to set the pointer on the vernier frequency readout directly above it to zero with reference to the built in 100kc crystal calibrator.

Operating Impressions

The CRM-R6A is a well designed, solidly built receiver. While not quite up to the standards of construction used in military radios the CRM-R6A is certainly in a different league from the amateur offerings of the period. The controls are well laid out and easy to operate. The flywheel weighted tuning control is smooth. With the exception of the sector control everything will seem familiar to the experienced operator of vintage receivers.

The receiver is sensitive, selective and stable. Absolute sensitivity is difficult to measure at my noisy urban receiving location but in general it seems the equal of the other high quality communications receivers in my stable. In the 6kc position the receiver copies broadcast stations well although the Radiomarine LS-1 speaker does not permit a good judgement of the receiver's fidelity to be made. The selectivity of the 3kc Collins filter is excellent as is to be expected. Somewhat surprisingly the 0.1kc audio filter works exceptionally well with no ringing. With the 3kc filter selected and the BFO set to an offset of about 1.5kc single signal reception is easily obtained.

I particularly like the AGC which has settings for slow, fast and off. I like slow AGC action and in the slow position the CRM-R6A provides just the right decay for my taste. In the fast position the AGC responds quickly making peaking of the antenna trimmer easy via the S meter. The AGC seems to work very well with the BFO on so I use it for copying CW. The noise limiter works reasonably well but is not as effective as the one in the RCA AR-88. On the other hand it is vastly better than the noise limiter in the Collins 51J-4 which hardly seems to have any effect at all.

The receiver is very stable. I have not done a formal measurement of drift but even at turn on one can just set the receiver on a signal and not have to adjust it. Certainly after warm up the receiver will simply stay where you put it with no further attention required.

In short the receiver is a pleasure to operate. And it has that certain something that gives great satisfaction of ownership, be it the appearance of the receiver in a dim room with its dial lights glowing or the solid feel of the sector control detents. If you find a CRM-R6A available for sale my advice is: grab it.