Collins R-390, 75S-3, 51S-1 & KWM-2A Receivers Compared

I have noticed over the years of having a Collins R-390 receiver (not the A model) made in the 1950's how wonderful the quality of audio is coming from the speaker. Also, the accuracy of the dial (after a quick cal) and the rock-solid stability of this vintage receiver make it a real pleasure to use. However, the sensitivity is a bit low and weak signals can be a challenge to copy. By coincidence, I had a RF amplifier made by Ameco (MFJ makes one also, model MFJ-1045C) that I connected to the antenna input of the receiver and improved the signal sensitivity by 20 dB (voltage gain). The purpose of this video is to help others with the R-390(A) or any other receiver boost the sensitivity of input signal while increasing noise floor as little as necessary. This simple improvement worked really well for me and it might help you also. 73 WA4QGA

[@peterarsenault2671]

That 390 is incredible!!! Could listen to it all day.

[@dougtaylor7724]

You and Mr Carlson could put on quite the measuring contest.

[@tatelandry6740]

I know I'm pretty off topic but does anybody know a good website to stream new tv shows online ?

[@nicholasethan7730]

@Tate Landry try Flixzone. Just search on google for it =)

[@ahmadibrahim7476]

@Tate Landry try FlixZone. Just search on google for it =)

[@moviestudioland]

What a great great video and teaching about mv and DB too.

[@elkabong6429]

The 390 sounds almost like FM on full quieting!

[@brianmoss5483]

Beautiful gear

[@craign8ca]

I miss my service monitor when I worked in two-way. All of my ham gear was tuned and run at optimal rx sensitivity.

[@ElPasoTubeAmps]

I have thought about buying a service monitor but as you know, they can be kind of expensive. Maybe I will luck out and get one at an estate sale. I paid $375 for my KWM-2A with power supply (516F-2), 312-B4 speaker/wattmeter/phone patch and and extra Collins speaker - the one sitting on top of the R-390. It is obviously a US government contract instrument as can be seen on the front of the power supply with the contract number. The 5R4 and 5U4 were in original GE tube boxes as was the fuse holder and fuse along with Collins tags in plastic bags. The way it came, it is apparent to me that it was never used before I got it. Got to go to estate sales before they put it on Ebay and it costs 10x as much.

[@MrElectrowhiz]

As far as clarity goes, the R590 and the KWM2 sounds the best to me.

[@ElPasoTubeAmps]

I know what you mean. Those two receivers have a more full-range frequency response than the other two but the 51S-1 and 75S-3 are more sharp or crisp sounding which can sometimes help get voice communication thru better. My favorite sounding one is the R-390. You might also find it interesting that the R-390 is only 500 ohm output and uses a little seven pin 6AK6 for 500 mW output to drive the local speaker and a 500 ohm line. I have been told a single stage 45 tube amplifier SET makes it sound even better.

[@mixradiointernationalshortwave]

A properly running 390 and A versions will have enough RF gain without a preamplifier. You may have a resistor in the IF for example that is high in value causing lower gain like I had in my 390. Once repaired and realigned it is a hot performer with my 390A.

[@ElPasoTubeAmps]

I am glad you mentioned resistor issues in the IF section. I have always figured it was in the IF section and I don't mind working on the unit but, as you know, work is to be done carefully and the beast is heavy for one old guy to move around. I may take a look in the IF section again. With the preamp, I would say it is as good as new. It is top-notch in performance but I would like to fix it properly. 73

[@mixradiointernationalshortwave]

@@ElPasoTubeAmps It could be something els too. I would check each IF tube plate resistor. The IF deck is not that hard to take out. I use a automatic AM sync detector with sideband. I also can run the IF output through a SDR board with power SDR or HDSDR software. Just amazing receivers.

[@mytglg6uh]

The S-3 will sound much smoother on ssb when you select slow AGC. Fast attack, fast release has always been problematic with Collins 75S-3's. Something to consider, unless you are a CW op. 73'S...

[@ElPasoTubeAmps]

Good point. I believe I discovered that long ago but forgot. Thanks. Also, the R-390 is a slow AGC as it has the Tree Top adapter on the back and it can cause a fraction of a second delay when the other station starts transmitting. Usually not a problem. I think the Tree Top adapter takes control away from the R-390 front switch. I will have to confirm that. In any case, the objective of this video is how the little bit of front-end preamp really brought the R-390 up to sensitivity performance very close or equal to the other receivers. I really enjoy using it. I have ordered another black rack just like what the KWM-2A is in to stack the R-390 and S-Line equipment and get some of my floor space back... may even buy a third rack later. 73

[@sammaloney2499]

I recently acquired a Collins R-390, I have no intentions of putting it into service,, what is a reasonable price for a unit.. it does power up... thanks Sam...

[@user-dn7js7rz2l]

Hi, was the lack of r390 sensitivity before you aligned it? R390’s have a very low noise floor in my personal experience

[@ElPasoTubeAmps]

Yes, the sensitivity was a bit low before the alignment and that is one reason I did a full alignment with the best tubes. The R-390 does have a very low noise floor and I like that. There seems to be something about the sound of the 500 ohm outputs on each of these three receivers that I like better than the 4 ohm outputs. I can't explain why could be. I added an outboard preamp and sensitivity is as good as my 75A-4 (a new addition) and my 51S-1 receiver. Interesting that I was listening to a very low signal level DX station last night and was switching between the R-390, 51S-1 and 75A-4. I think most of the difference was just in the speaker sound and not the receivers as each receiver had its own characteristic sound all actually very good. This was on 40M. The R-390 is still top-notch compared to any receiver.

[@cheesedoodlefeeder]

I dunno, a $100 Sdrplay sounds pretty nice, hears and displays everything and takes up much less room.

[@ElPasoTubeAmps]

The SDR is pretty amazing and does just as you say but I love the old technology and keep the boat anchor equipment running. I can fix the old stuff but if the SDR breaks it goes in the trash can and I have to buy another. I mostly use my SDR nowadays as a spectrum analyzer. The modern stuff is amazing and I like it also.

[@johnsweda2999]

Did you get my last comment I never got a response about micro cap,I left you a link so maybe it was in spam

[@ElPasoTubeAmps]

Hi John, Yes, thank you, I did get your message about Micro-Cap and did use it some years ago when it was only a DOS version. I still have that DOS version on floppy. I did download and install the Windows 10 version of Micro-cap on this PC. I am not as familiar with Micro-cap as I am LTSpice so I have a bit of a learning curve to get thru... I looked up Micro-cap and found this link for new downloads for others that read this and might be interested. Also a link to LTSpice direct from Analog Devices. . . www.spectrum-soft.com/download/download.shtm www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html#

[@johnsweda2999]

@@ElPasoTubeAmps ok that's fair enough, not much difference between that and ltspic is there both do the same thing? Is ltspice free? Glad you found it useful. Just curious do they give you different results if you got the same circuitry running in Virtual.

[@nowayhunting]

i have 2 collins kwm-2 with instruction book. collins 30L-1. collins speaker. swan FP-4 phone patch. curtis mathes power supply. swan mark II power supply. swan mark II linear amplifier with operation and maintance book. maco 500. swan model CM17L micro phone. Shure MOdel 450 micro phone. some cords look bad, would not plug in. my Dad passed away in 2018 and he left these to me. have no idea what they are worth other than had offers from 500.00 to a guy in Utah said if he was closer they would be worth 2500.00 to him. i won't ship and he won't come and get them. any body tell me what they are really worth? taking up space at my house. thanks, Bill in St. Joseph, Mo.

[@ElPasoTubeAmps]

Hi Bill, I am very sorry to hear about your Dad passing. I actually worry about my stuff when I pass... just my opinion here - selling locally like at an estate sale, you are likely to have to sell pretty low. I bought my Rockwell Collins KWM-2A with power supply and speaker in absolute mint condition for $375. On Ebay people would likely ask several thousands for it - and possibly get it. I was given, for free, a Collins 30S-1 a few months back. It needed a little work but it was a couple hours work to put it back in perfect shape. What does all this mean? Most people today want auto-tune, plug and play solid state equipment and are not capable or interested in repairing and maintaining vacuum tube equipment. Similar to old cars. There are exceptions.. Not too many left that even know how to operate the Collins S-Line equipment. Some might want it for a museum piece. I am sorry to say that. On the other hand, you could run across a person passionate about the vintage equipment and get a decent price. Once again, this is just me talking as I have bought a good bit of other equipment around here in El Paso from estate sales and often times the sellers start asking prices comparable to Ebay prices but - be prepared for this - often times things sell for about 1/6 that price at estate sales. A $600 item on Ebay may likely sell for $100 at an estate if there is any one even interested in the older equipment. I am sorry to tell you this but it is true where I live. It may be different in your area of the country. Other people may give you more hopefully thoughts and better advice on selling this equipment.

[@nowayhunting]

@@ElPasoTubeAmps thank you. like anything else. find the 1 person that wants it and let him or her make offer. rather see someone thats going to use it buy it. i know nothing abut these radios. they dont eat much so i can hold on to them. thanks again, Bill.