Collins S-Line

KWM-2

Enlarged Photos and Descriptions
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Right

You just have to love this gear. They look like real radios and better yet, they set the standard of performance for many years. Heathkit heaped tons of flattery on the S-line by producing as close a copy as they could. However, it took the Drake C-line to reestablish the performance standard. The Jap junk didn't do it until rigs like the TS-930S came along. I didn't give the credit to the earlier Drake rigs because the C-lines predecessors just didn't have adequate filtering (just my opinion, of course).

Even after nearly 30 years, the Collins S-Line is perfectly capable of handling today's crowded bands. Though not digital, the PTO's (VFO's) have remained linear and on frequency. It's easy to set the frequency to within a hundred cycles or so. What makes a really nice rig to join in with the boat anchor crowd is a KWM-2 paired up with a 75S-3 receiver. The 75S-3 is much less expensive than the KWM-2's companion 312B-5 external PTO and station console and using a separate receiver will give you some very useful useful features - like dual receive, transceive, transceive in different band segments, receiver with a notch filter and a 200 cycle CW filter, etc. And, if all this wasn't enough, the KWM-2 sounds really nice on the air and its receiver's audio is quite pleasant to my ears.

In the video capture above, there are actually two completely separate rigs. On the first level is a KWM-2 with a Water's rejection notch. To its left is the semi-rare and ridiculously overpriced 312B-5 station console. It serves as the second PTO (VFO) for the KWM-2 and is complete with switching for transceive and separate, two PTO operation. Also included is a phone patch and a watt meter. (Like I mentioned above, you can save money and have all the advantages of two VFO's for split operation by adding a 75S-3 instead of the 312B-5) A 30L-1 linear is on the right side of the KWM-2 and the 516F-2 power supply is on the far left. Again, you see a venerable, old D-104 microphone which is plugged into whichever rig is in use.

On the second level is a bit of a mixture. Starting from left to right is a power controller supporting a second 516F-2 power supply for the 32S-1 transmitter immediately to the right. Next comes a 75S-3 receiver and finally another 30L-1 linear.

The monitor scope sitting atop the 32S-1 is only temporary. It's proper location is on operating position #4 just to the left of this picture. Again, like the main operating position and the "Gold Dust Twins," the monitor scope, antenna switching, and other accessories are within easy viewing range but located at another operating position. This keeps the visual integrity somewhat correct.

Eventually, a 312B-4 will replace the power supply on the top level and the power supply will be relocated to the floor.


This is a nice, pleasant operating position. It is not entirely ergonomically correct, (the desk is not deep enough) but most of the controls are within easy reach and meters can be read without much effort. If you look close, you can see that the gear is arranged with the front panels angled toward the operator. It wastes a lot of wood when cutting the shelving, but the appearance and ease of operation are worth the effort.

Generally, when I operate from this position, I use the S-Line. If the location of the gear was switched I'd use the KWM-2. It's just more convenient to use the gear on the shelf.

A Critique and afterthoughts -

75S3 Receiver

As far as the performance of the equipment goes, I like the 75S3 receiver. The 75S-3B and -3C models are more in demand, but the straight old 75S-3 performs well and features a built-in 200 cycle CW filter. It's a crystal filter and not the usual Collins mechanical variety. I wish it was. A 200 cycle bandwidth mechanical filter would be something to behold! Still, this filter is obviously quite sharp, but has an inordinately low ultimate rejection (blowby). I haven't measured it yet, but I guess the ultimate rejection to be -50 to -60 dB. I don't know if it's the filter or improper shielding which contributes to the CW filter performance. I was expecting much more out of that filter. Actually, the problem is compounded by a very tight AGC system. The receiver has far more gain and AGC control range than the filter has attenuation. So, out of passband signals are simply treated to extra gain by the AGC system which is doing its job keeping the level of all signals the same. Reducing the RF gain helps.

Now that I have had my complaint about the 75S-3, let me say that I think the 75S-3 is an incredible receiver bargain. I haven't found another boat anchor that even comes close to this level of performance except perhaps the Drake R4C. Some day, I want to do a side-by-side test of a stock 75S-3 and a stock Drake R4C. Of course the passband tuning system in the Drake will give it a definite QRM fighting advantage.

Most collectors and users want the later B or C model and overlook the plain-Jane 75S-3. This has kept the cost of this receiver at a reasonable level and it is a nice boat anchor addition to any shack.


Power Distribution

One weakness in the KWM-2 and 32S-(all) is the on-off switch. It's not that they fail often, it's just that after all these years, they do fail. On top of that, the on-off switch in the 30L-1 is quite difficult to change and it gets lots of use because you have to turn off the amplifier to bypass it. The solution I have chosen is to leave all of the equipment turned on and use a quality computer power distribution box to turn the equipment on and off remotely. We'll see how it works out.

32S-1 Transmitter

There is not much to say about the 32S-1 except that it, like the KWM-2 is a real workhorse. It does just what it's supposed to do - transmit good sounding SSB and stay on frequency. It does just that, so what more could you ask of a transmitter designed in the late fifties. The only real fault is the way the 32S-1 generates CW. Collins engineers chose to use a keyed audio oscillator to produce CW. It's a neat trick and simplifies adding CW to a SSB rig. If the audio tone generator is pure enough and the sideband rejection infinite, all would be wonderful. In this application, all is not wonderful and you may find that you are transmitting on two frequencies about 3 KHz apart. One signal is only down 40 to 50 dB from the other. However, if you don't plan to work CW, then this 32S-1 is a fine sounding rig and it drives the 30L-1 linear with power to spare. When all adjustments are proper and the correct interconnect coax between the 32S-1 and the 30L-1 is used, this is one clean rig. Distortion products are down as much as 40 dB or more. Try to get that kind of performance out of a solid-state rig.

KWM-2 Transceiver

I don't what it is about KWM-2's that makes them so much fun to use. There's not many knobs to twiddle and there are no QRM fighting features other than the excellent 2.1 KHz mechanical filter, excellent gain distribution and the inherent linearity of the receiver section. Or, in a word, Collins engineering.

Perhaps it's just that everything looks right, sounds right, and feels right. Signals are a pleasure to tune and the big tuning knob is as smooth as silk. And, although a relatively narrow passband of 2.1 KHz is used, stations with good audio sound really nice on a KWM- 2. Fortunately, Collins made thousands of these, so just about everyone can have one.

30L-1 Linear

This amplifier is the best kept secret in ham radio today, and it is my favorite medium power linear amplifier.

At first glance, you know something is different (or broken). The panel meter sits about 1/3 of the way upscale even when the power is off. Actually, that's the way it's supposed to look and that special meter is a dead giveaway that an unusual and very effective phase comparator circuit is used in this amp. The input signal is compared against the output signal. Except for their amplitude, they should be identical. After all, this is a linear amplifier. If the output flat-tops, or the amp is improperly loaded, or the input is over driven, distortion products immediately develop and you can see the result on the 30L-1's meter. It's a handy indicator when a monitor scope is unavailable.

I run these amps on 120 volts and get about 650 watts out. The difference between 650 watts and 1500 watts, the legal limit, is just slightly over 3 dB. You would be hard pressed to tell the difference between a 30L-1 and a full legal power amp on the air. Best of all, the 30L-1 is a very convenient size, is of reasonable weight. It is built to last.

I hope you're enjoying your tour. It's fun showing you around the shack. Let me show you the next operating position.. Interested? Great.


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An unusual operating position!