| W9LBB |
Rating:  |
2019-09-11 | |
| A good, reliable, vintage workhorse receiver |
Time Owned: 3 to 6 months. |
Let's be clear about one thing from the start... I consider Collins receivers to be SECOND RATE receiver designs. My tastes run more toward Racal and Watkins-Johnson equipment, but when I pair up a receiver with a transmitter, the whole game changes.
I recently acquired a nearly complete Collins S Line, something I drooled over when I was a kid. It's first generation, the serial numbers placing the 32S-1 transmitter and 75S-1 receiver at 1959.
I must admit that I was impressed by the 75S-1. It's a relatively simple receiver design that gives a lot of performance in a fairly compact, easy to use, and light weight package. Once I'd obtained a used pull-out CW filter upgrade kit (the receivers left the Collins plant WITHOUT them!) and installed it, the beastie became a pretty respectable CW receiver that could ALMOST hold it's own in pileups (more on that later).
The rig is simple enough that when it breaks down, you can fix it YOURSELF with relatively simple workbench tools. No crating it up to send it back to the factory.
The only problem... being vintage gear, the rig doesn't cover the WARC bands,let alone 60 meters.
When a 75S-2 became available at a decent price, I jumped on it too.
The 75S-2 is virtually identical to the 75S-1, with one big difference; it includes a second crystal deck which adds 14 more 200 KHz wide bands of coverage.
A small number of 75S-2s were made (reportedly, 300 - 400 units) for commercial and government users who obviously wanted to cover more than the amateur bands. Reportedly, the 75S-2 is a sort of scarce model.
Since I'm tinkering with a basket case KWM-2 transceiver right now, along the way I've obtained a long gone out of production Collins accessory, the CP-1 Crystal Pack, which provides crystals for operating the KWM-2 on any frequency between 3400 - 5000 KHz and 6600 - 30,000 KHz.
The CP-1 crystals are also used in the S-Line rigs.
Installing crystals for the WARC bands was simple... I was even able to install them in the same crystal bank as the rest of the ham bands, adding the appropriate frequency tags to the sliding card in the bank selector. The existing crystal for 14.8 - 15.0 MHz band switch position (used for WWV calibration) was removed, and replaced with a 10.0 - 10.2 MHz crystal, providing WWV coverage as well as the 30 meter amateur band.
The one crystal that Collins provided for 10 meter coverage (28.5 - 28.7 MHz) was moved to the last place in the three 10 meter slots in the receiver, and crystals for 18.0 - 18.2 MHz (17 meters) and 24.8 - 25.0 MHz (12 meters) were plugged into the other two spots, and appropriate tags were added to the sliding bank selection switch card.
After that, recrystaling it got sort of strange.
Collins never produced crystals for 5.0 - 6.6 MHz, so 60 meters was a problem. However, in the coffee can full of stray crystals in my workshop there was, much to my surprise, a rock for 8355 KHz that filled the bill. It gives a tuning range of 5.2 - 5.4 MHzI
Plugging it into an empty spot in the second crystal bank, I found that it WORKED PERFECTLY! To make it even better, there's enough dial end slop to cover the 60 meter channel at 5405 KHz!
I have some of the other crystal slots loaded up with rocks from the CP-1 to cover the 31 and 19 meter international broadcast bands, and several military aviation frequencies that I like to monitor.
I work a lot of CW, and I really wanted another CW filter kit to add to THIS rig too, but it was not to be... until I checked the work shop junk box again.
The original Collins filter kit consisted of a 500 Hz mechanical filter, and a BFO crystal at 455.800 KHz. The 500 Hz filter is a bit wide for modern band conditions, but it's a BIG help.
My junk box search yielded up a plug in mechanical filter meant for a much later Collins / Rockwell receiver, with a bandwidth of 300 Hz. A web search showed it's specs to be very close to those of the original filter. I got hold of a 455.800 KHz crystal, soldered leads to the filter's plug-in pins, and sticking it in place with double sided tape (the original mounting clip didn't fit) I gave it a try.
It worked... very nicely, thank ya very much! And that 300 hz bandpass is a distinct improvement over the original 500 Hz filter in crowded band conditions.
As for the receiver's performance...
PROS
The 75S-1 and -2 are VERY stable receivers. Except for the permeability tuned VFO, every oscillator in the rig is crystal controlled. After a 15 - 20 minute warmup, they don't drift any appreciable amount.
The Collins dial mechanism is a joy for anyone who ever learned to use a slide rule! You can "guestimate" frequencies to within 100 Hz with practice... and it's SMOOTH too.
RF sensitivity is quite good; don't sell tube front ends short. It even cooks on 10 meters.
Overall, a simple to use receiver that a good operator can run quite effectively.
CONS
Like I said... I consider Collins designs to be second rate receivers. It's FULL of birdies... very weak ones, to be sure, but for someone who is accustomed to the silky quiet of Racal and Watkins-Johnson "Premium" receivers, they stand out like a sore thumb. Racal and Watkins-Johnson designers put in a LOT more effort to eliminate spurious responses... but then, even tho Collins gear was expensive, it was DIRT CHEAP compared to the Big Boys!
As I said earlier... the rig is ALMOST up to snuff for handling pileups and crowded bands during CW contests, but not quite there. And Collins knew it. Something more is needed.
At one time, Waters offered an internal Q multiplier kit to give the S Line rigs and KWM-2 more to work with on CW; the 75S receivers have an RCA jack on the chassis to plug the Waters option in.
The Waters Q multiplier is long gone now... but I am happy to report that the ancient Heathkit Q multiplier, when plugged into that jack, gives you everything you could ask for in terms of selectivity!
I'd say that the 75S-1 and -2 do a pretty decent job for 60 year old receivers. I'd recommend 'em both.
If the Watkins-Johnsons are the Rolls Royce of receivers, I'd say that the 75S-1 or -2 is a Cadillac!
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