View Full Version : 75-S3(A) vs. 75A4

01-05-2007, 02:51 PM
I used an 'A4 in college in the late 60's, and I've had the -S3A (also an -S3) since '91, so there were 20 years between the two and my memory might play a part here.

But here's my take (almost all subjective):

"Sound and Feel"

(BTW, I was a true S-Line virgin when I got the S3A in '91. #I had only ever seen S-line "in person" a very few times at a dealer and had never played with one.)

My first very stong impression of the S3A when I first turned it on was that it sounded and felt as good as, and maybe even better, than the 'A4 I used in college. #This was a complete surprise to me. #I had expected the 3A to resemble the other radios of that era more than the 'A4, but it didn't at all.

And, that immediately became the station receiver once I had my fill of some other boat anchors, notably a GPR-90. #Especially since the 'S3(A) has IF can selectivity and a diode detector for AM. #(Another surprise!)

Going beyond look and feel, there's the construction and design differences between the two receivers.

The 'A4 is big and heavy with many more parts, while the 'S3 is "less big", lighter, and with fewer parts, read, more reliable. #This is where my respect for Art Collins went through the roof. #I see the s-line as a streamlining of the A receivers without sacrificing operating goodness. #The simple, but effective and reliable mechanical design of the preselector permeability tuning (exciter in the 32's) was a "wow" for me. #

Features & conveniences...

The obvious one is the 1 Mc vs. 200 kc PTO ranges. #Yep, it's a pain to go from, say, 3799 to past 3800. #I rationalize that inconvenience by reminding myself that a 200kc range is easier and cheaper than a 1 Mc. range. #What I haven't researched yet is how do the tracking of the two match?

The 'A4 has passband tuning. #The 'S3A can do it in a kludgy way with the BFO pitch. #So, while the capability is there, it's a pain. #But, the 'S3A has a notch while the 'A4 doesn't.

And, yes, ya gotta peak the preselector on the 'S3A.

What I haven't really done is learn the relative technical receive capabilities between the two. #I'd guess that the sensitivity and selectivity are darn close to each other, but intermods, birdies, noise, etc., is what I don't know. #Subjectively, they seem pretty close, but then I don't really use it where those would be evident.

So...I would definitely not replace the 'S3(A) with an 'A4. #Another time and place I'd love to own an A4 to get re-aquainted with it, but for now I'll enjoy my superb 'S3A.

BTW, in the short time I had them both set-up, I didn't notice that much difference between the 3 and the 3A except for the extra crystal bank.

And another comparison. #My SSB station just before the S-line was a cherry Drake C-Line. #While they were superb instruments, the S-line completely trumped them in sound and feel.

01-05-2007, 04:38 PM
Unfortunately, I've never had these side-by-side! Glen K9STH probably has.

I've owned two "S-Lines," the later one was the "B," so I had a 75S2B for five years -- but that was back in 1973 or so. I loved the setup and it worked very well. At that time, I didn't have a 75A4 so I never could compare them directly.

Now, I haven't had an S3B for many years, but do have a 75A4. I bought the A4 third-hand about twenty years ago and it's in about as "mint" condition as a piece of 51 year-old equipment can be. It is an awesome receiver, and there's nothing that any modern rig can hear that the A4 can't hear at least as well -- often, better. I have the three filter slots filled with a wide (6 kHz) AM filter, the standard SSB filter, and a narrow (500 Hz) CW filter. Although it's physically large, it's smaller than the 75A1-A2-A3 were, and not heavy at all. Also, and rather amazingly, despite its large tube count, the 75A4 only consumes 85W when operating -- less than one ampere from the 120Vac line. For its age, that's really cool. And cool it is, the receiver generates virtually no heat.

This would be a tough choice for me, especially since I've never had them side-by-side. But I'll keep the A4, especially since I already have it! Now, to find that KWS-1 for $100...



01-05-2007, 06:25 PM
I have in my posession right now a 75S-3A, two 75S-1, a 75A2, 75A3, 75A4, and a Heath SB-301 receivers. I have owned a 75A1 (s/n 4), a 75S-3, and a Heath SB-303.

One of my 75S-1 receivers has the Waters "Q"multiplier ("notch filter") and the other has the 500 Hz mechanical filter plus alternate BFO crystal. My 75A2 has a product detector installed in the NBFM socket and my 75A3 has the NBFM adaptor installed. My SB-301 has all 3 filters (AM, SSB, and 400 Hz CW) installed. The 75A4 has an 8 KHz AM filter, a 3.1 SSB filter ("standard" for the 75A4) and a 2.1 KHz SSB filter.

As I mentioned in another thread I traded off my 75S-3 for an even trade for a 75A4 a number of years ago. The 75S-3 worked very well. However, the person that I got it from had lived near the Gulf of Mexico (in the Houston, Texas, area) and the chassis had been discolored by the salt water atmosphere. But, I owned the receiver for well over 25 years and never had any problems with it. I did make the Collins recommended modification which moves one of the 455 KHz i.f. cans from the AM filter to tune the output of one of the mixer stages. This definitely improves the performance of the receiver (and I have done this on all of my other 75S- series receivers).

The 75S-3 series receivers have the advantage of being able to transceive with the 32S- series transmitters. This is a definite advantage when working SSB. They also work better on SSB than the 75A4 (although the 75A4 is no "slouch"). AM operation is "OK" on the 75S-3 / 75S-3A (same receiver except for the additional crystal deck) but is better on the 75A4 IF the wider mechanical filter is installed. But, the 75A3 sounds better than the 75A4 on AM and the 75A2 is the best sounding of the three "A" Line receivers that I have right now. Many amateurs believe that the 75A1 is the best sounding of the "A" Line receivers but I traded mine off in the late 1970s when you had to almost pay for someone's gasoline to haul the old equipment off (definitely wish that I had it back).

The 200 KHz band coverage of the 75S- series is a definite "draw back". I have used the additional crystal deck in my 75S-3A to add different coverage from the "standard" bands (i.e. I have 7100 KHz to 7300 KHz which gives me the entire SSB region on 40 meters as well as the 7000 KHz to 7200 KHz and 7200 KHz to 7400 KHz ranges). In addition, I have added one of the "no holes / no wiring changes" crystal decks that I manufacture to my 75S-3A so that I have the entire 10 meter band, 12 meters, 17 meters, 30 meters, and 60 meters in addition to the "normal" coverage of the 75S-3A. I have also added one of the AADE digital readouts so that I now have the capability of reading frequencies down to 10 Hz instead of being able to read the analog dial to around a 200 Hz accuracy.

The 75A4 has held its value for many years and the receiver is "worth more" on the market than the 75S-3 receiver. The 75S-3A is a much rarer receiver (only about 500 ever made) and thus the 75A4 is not worth more than the 75S-3A. That is why when an amateur on the west coast wanted to trade me an excellent condition 75A4 for my 75S-3 receiver with the discolored chassis that I definitely made the trade.

Now the 75S-3 and 75S-3A came from the factory with the 200 Hz CW filter installed. EVERY 75S-3 and 75S-3A came with this filter and if you find one without the filter someone has removed it to sell "on the side". The 200 Hz filter was an expensive "option" on the 75S-3B and 75S-3C. The 75S-1 and 75S-2 had a 500 Hz mechanical filter as the CW option. This filter is VERY handy to use when it is desireable to "dig out" a CW signal that is either "down in the mud" or else covered by QRM. However, you really need to use the variable BFO instead of the crystal BFO when using this filter because the audio tone with the crystal BFO is very high pitched. Also, the 200 Hz filter tends to "ring" unless you are careful to reduce the r.f. gain control.

The 75S- series does NOT cover 160 meters. There have been some very "klugey" modifications to get the receiver to cover 160 but those are generally not that good. I use my 75A4 along with my Hammarlund HX-50A transmitter on 160 meters.

The 75A4 is better on AM than the 75S- series. It is better than the 75S- series on CW IF you have a narrow filter. The 75S- series is better on SSB than the 75A4. The 75S- series can transceive on SSB whereas the 75A4 really cannot. The 75S- series is MUCH smaller in physical size than the 75A4. As such, it is a "toss up" as to which receiver is better. If you operate primarily SSB then the tendency is towards the 75S- series. If you operate CW then the tendency is towards the 75A4. Of course the best thing is to own both types of receivers!

Now the 75A2 and 75A3 have an advantage over both the 75A4 and 75S- series when used with VHF/UHF converters. Those receivers, along with the 75A1, cover the 26 MHz to 28 MHz and the 28 MHz to 30 MHz ranges in 2 complete bands. This makes using them as i.f. for 6 meter and 2 meter converters "perfect". Also, you can cover the entire 222 MHz band (3 MHz wide) and 4 MHz of the 432 MHz band without any problems.

The Heath SB-301 covers 500 KHz in each band range which gives full coverage of the 80, 40, 20, and 15 meter bands. The 10 meter band comes "standard" in 4 ranges each 500 KHz wide. This is an advantage over the 75S- series. I have found that the SB-301 can do anything that the 75S-3A can do 9 times out of 10. But it is that 10th time that makes the 75S-3A more useful.

Anyway, I can go on about the differences between the various receivers. However, in general, I have outlined the primary differences.

Glen, K9STH

01-05-2007, 07:04 PM
Glen, you simply have too much stuff! http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

Actually, I'm envious. My "downsized" hamshack (in a spare bedroom that's only about 10' x 13' -- smallest room in the house) wouldn't accommodate all that, but I have a big garage and might start "accumulating" again, as I once did years ago in NJ when I had a 16' x 24' hamshack with separate operating stations for each band.

I built the SB-301/SB-401 (as well as an SB-110A, SB-220, SB-610 and lots of stuff) back in about 1967 or 68 and they worked very, very well. Not as mechanically robust as an S-line, though, and one "weakness" was the LMO drive/dial indicator system. The Heath cabinetry wasn't quite as nice, nor the fit & finish, as Collins. I remember the S-line evidently had high quality pots and switches, as I can't recall ever seeing any wear out, even after tons of use over years.

My 75A4 had its 51st birthday and to this day, if I dial up WWV at 15.000 MHz when the receiver's "cold" and has been off for days, and turn the receiver on, the first thing out of the speaker is a zero beat with WWV's ticking modulation. That's damned good for a 51 year-old receiver!


01-05-2007, 09:07 PM
Very interesting info, Glen.

I spent the first 10-12 years of my ham career using my Dad's much-modified 75A-3. I compare all other receivers to that standard.

A good friend of mine had the 75S-3, can't tell you which version. I always thought it worked at least as well as the A-3. Plus, it had a noise blanker that was just amazing. This guy had a powerline that was 60 over S9 in his backyard. With the NB on, it was gone. The only one I've ever seen close to that was one of the Drake TR-4 models. Both of those units employed a separate noise receiver whose output was fed out-of-phase into the IF to wipe out impulse noise.

I found the SB-line comparison interesting. I think my radio club still has a pair of those real cheap - I better get my bid in! Again, the SB/HW Heathkit lines were not at all bad. The Yaesu FT-902DM probably had the most Collins-like audio of any 'modern' radio.

01-07-2007, 10:17 AM
Thanks, Glen, I sure appreciate you taking the time to go into that kind of detail in the comparison. #Actually, considering my expreience and your comments it's more like two separate descriptions rather than which is better.

The additional comparison with the SB-300 was great to read, too. #As an SB-102 owner/operator (at least while the LMO was bahaving #http://www.qrz.com/iB_html/non-cgi/emoticons/biggrin.gif ) we kinda thought that, but of course, couldn't be sure. #An, WIK, you comments about the fit and finish are exactly right. #While it was good when I finally got the dial drive "right", It was a REAL PAIN getting it there. #(And I had to do it multiple times in changing the LMO's!) #I also had an SB-401 I got at a hamfest ($75, I beleive), and after I replaced some fried final cathode resisters it was a great transmitter.

One "quirk" in my '3A is that the switch on the BFO control must have broken because it's not a push-pull type, the switch is the conventional ON/OFF-volume control config. #But, it work FB. #Yea - it's necessary in CW!

Thanks again.


01-07-2007, 02:10 PM
GUH I have never seen an S3 with a push button switch. The BFO is rotary, with an OFF position.

01-07-2007, 02:31 PM
Quote[/b] (W0LPQ @ Jan. 06 2007,08:10)]GUH I have never seen an S3 with a push button switch. #The BFO is rotary, with an OFF position.
Y'know, I had that thought while I was composing that last post. Do you know why? #A lot of times I wished it was push/pull so I didn't have to find the right position every time I turned it "on."
#Well, that's another difference between the
'3 and the '3A.

Thanks a bunch for the info!

01-07-2007, 04:36 PM
The 75S-3 BFO switch is identical to the 75S-3A. That is, it is a conventional "volume control" switch. All of the 75S-3 series receivers use this. The 75S-1 and 75S-2 as well as the KWM-2 series do not have a variable BFO. This is why when the optional 500 Hz mechanical CW filter is installed in the 75S-1 and 75S-2 a separate BFO crystal is supplied so that the CW tone is not high pitched. The 75S-1 and 75S-2 also do not have any means to turn off the AVC. In fact, the AVC in those receivers is fixed at "fast attack / slow decay" whereas in the 75S-3 series you can turn off the AVC and choose between "fast attack / slow decay" for SSB and "fast attack / fast delay" for AM. The KWM-2 series is the same as the 75S-1 and 75S-2 in terms of the AVC.

The 75S-1 and 75S-2 do not have a "notch filter" installed. They do have an RCA jack on the chassis for plugging in an external "Q" multiplier (the Heath QF-1 works great with these receivers). However, Waters did make an "after market" conversion kit to add a "notch filter" to the 75S-1, 75S-2, and KWM-2 series. I added this kit to my original 75S-1 and it does work very well.

The tunable BFO in the 75S-3 series is really designed to be used with the CW filter (200 Hz came in all of the 75S-3 and 75S-3A and any CW filter is a high priced "accessory" in the 75S-3B and 75S-3C). For SSB operation you really need to use the crystal controlled BFO (and to transceive with the transmitters on SSB this is an absolute necessity). Art Collins (founder of Collins Radio) had a really "strange" policy where the 500 Hz mechanical filter for the 75S-1 and 75S-2 was concerned. He absolutely refused to allow any new receiver to be shipped from the factory with the 500 Hz filter installed! You had to buy the receiver and then either installed the CW filter (and the optional BFO crystal) yourself or you could return the receiver to the factory and then the filter would be installed. But under no circumstances was the CW filter to be installed when the unit was built. Who knows why Art Collins had this policy! Art was definitely a "strange dude" at times (I only met him 3 times during the 2 years that I worked for Collins Radio but got to know him better after I left the company and he sold out to Rockwell International).

I have a 75S-1 which actually cost a Collins Radio employee his job due to the CW filter. It was the policy of Collins Radio that any employee could purchase amateur radio equipment at a price below wholesale. Back in the late 1950s, when the 75S-1 and 75S-2 were current production, one of the Dallas area employees purchased this 75S-1 through the employee program. Since he wanted the CW filter he "made a deal" with someone in Cedar Rapids to have the filter installed when the receiver was built. Within a few days of receiving the receiver Art found out about the filter being installed at the factory. Rather than try to "face" Art's wrath, the employee immediately quit his job at Collins Radio.

Shortly after leaving the company the employee traded the brand new receiver to another amateur operator (who didn't work for Collins Radio) in Mesquite, Texas (Dallas suburb). This fellow had a complete S-Line and just put the receiver in his garage where it sat for over 40 years! In 2004 this amateur traded the receiver to an amateur who lived in Terrell, Texas, for some closed circuit television equipment. I had an older Aerotron 450 MHz community repeater that I had used commercially for a number of years that I had retired and it was sitting in my garage. The Terrell amateur wanted the repeater and traded me the Collins 75S-1, a brand new Telewave wattmeter, and a pretty good amount of cash for the unit.

Frankly, I did not know that the 500 Hz filter was installed nor did the person who traded it to me know that it was there. I was checking the receiver and discovered that the filter was installed. After contacting the person from whom I had obtained the receiver he checked with the fellow that had the receiver in the garage. That is when the situation about the CW filter became known. The only thing that was "wrong" with the receiver is that the power cord insulation had become cracked from over 40 years of storage in an un-airconditioned garage in the Dallas area.

The 75A1, 75A2, and 75A3 have separate controls for turning on the BFO and for the BFO frequency. The 75A4 is completely different in the way the BFO works. In the 75A4 the BFO is a fixed frequency. When you tune the "passband" you actually are rotating the PTO ("VFO") and changing the the injection frequency. However, do to the dial drag adjustment the 100 KHz circular dial does not move.

If you look inside the receiver and move the passband control you will see that the PTO actually rotates! Also, if you loosen the dial drag too much the 100 KHz dial will move when you tune the passband. The 75A4 is the only receiver that I have seen that does this.

Anyway, it is really impossible to compare the 75S-3 series with the 75A4 on an equal basis. Each receiver has its advantages and disadvantages when compared with the other. Thus, as I said in my original post that the best thing is to own both receivers!

Glen, K9STH

01-07-2007, 07:06 PM
Quote[/b] ]The 75S-3 BFO switch is identical to the 75S-3A. #That is, it is a conventional "volume control" switch. #

So one of my receivers is not stock. # My '3 turns the BFO control by pushing and pulling (out = on), my '3A has the switch where it is turned off at max CCW rotation of the control. #I guess both are conventional ON/OFF volume controls. #I'm going to guess that the configuration of my '3 that's stock. #But mebbe not...maybe Collins used both. #http://www.qrz.com/iB_html/non-cgi/emoticons/rock.gif

Quote[/b] ]Art was definitely a "strange dude" at times

What genius/artist isn't? # http://www.qrz.com/iB_html/non-cgi/emoticons/biggrin.gif

Thanks again for your Collins lore, Glen.

01-07-2007, 08:56 PM
It is your 75S-3 is that not "stock"! All of the 75S-3 series use the switch that operates like a "normal" off-on-volume control in an old AM radio. That is, you turn the knob fully counter-clockwise to turn the variable BFO off. When you start to turn the knob clockwise the variable BFO turns on.

Since the variable BFO was really designed to be used with the 200 Hz filter the only reason that I can see why someone changed the switch out for the "push-pull" type is that they found the "spot" that they really liked for the tone when using the 200 Hz filter and did not want to have to reset the frequency each time that they used the filter. Frankly, I like to vary the tone when I am using the filter. Sometimes this allows me to "null out" QRM that is within 100 to 200 Hz of the desired signal making the signal much more readable. Also, I get tired of hearing the same tone time after time!

Glen, K9STH

01-07-2007, 11:52 PM
Ah, OK, Glen. #I had it backwards. #And the previous owner did the mod. #OK, since I thought the push-pull was the better based on actual operation, and I knew the previous owner was a very knowledgable ham (see below), he did, well, from an opeartor's point of view (at least from my experience), the right thing. #What I'm saying is that the push-pull felt like the natrual scheme of things.

OK...it was a great sale. #It was an estate sale being hosted by another truly great ham. #I sure wish I could remember his name or call. #I went to his home, and then we drove over to the estate sale. #The S-line had been up on the shelf for years, but he pulled 'em off and opened 'em up for me to examine. #On one of them, that bar for the exciter or preselector tuning was stuck. #I pointed that out and what he did was physically force the bar down to free it up. #He did it as a long experienced S-line guy. #Ok. #just some personal Collins lore.

He also was the guy selling the KWM-2A and the GR bridge I got that day.

And, to top it off...

That was my second choice in the ad. #The item that I was most interested in was a home-brew 4-1000 plate modulated AM transmitter. #I really wanted that, but in retrospect, the S-line wasn't just a consolation, it was fate taking me to the radio that was for me.


01-08-2007, 03:27 AM
GUH if I would have mashed on the slug rack in Cedar Rapids ... I would have been shot. That is a no-no.

A little bit of lubricant on the slugs and gear train is much better. He could have broken a slug screw or tore the housing inside the can rack.

Bill, W0LPQ/9

01-27-2007, 07:00 AM

Yep...I was aghast when he did it. But the results, and my later experience was that he was a total Collins guy. He had operated several rigs and really knew, in depth, their characteristics.

But that's not why I resurrected this thread...

If you follow Questions and Answers, you know that I recently found out what to use for an antenna for my 'S3A, and its just now that I can tune into a roundtable and listen to what S-line can do.

Specifically, I want to mention the AGC action. Again, it's purely natural and just right. It doesn't have the obvious "fast attack, slow decay" of Drake.

But the background noise doesn't pump. Nothing pumps. The time constants and action are so well tuned that you don't even know the AGC's working until you turn if off.