The AM Forum

Hi all!

Long-time lurker, first-time poster here.   :)

I'm getting all of my equipment together to get my AM station on the air.  I have one piece of equipment that I know I've seen before, but I can't think of the model number and/or maker's name.  Of course, the nameplate is missing.

I've attached a photo of the mystery item.  Anyone recognize what it is?  Also, would it be useful for on-air use?

Thanks and 73,
- Greg K2GTM

Don't hold me to it Greg, but I'm pretty sure it's an audio amp/preamp used by the FAA. I've got a couple of these up north that I haven't seen in years, they came out of Knapp airport in Berlin, VT back in the mid 80s. They still have the tags, though difficult to read from 800 miles away.

Do a search on ebay, they turn up on there from time to time. Should be able to turn up a tag or other info.

Hi Greg,

That is an audio limiting amplifier built in large quantity back in the 1950s (to a U.S. government contract) for use primarily by the FAA. It was used to keep their ground-to-air AM rigs from overmodulating.

It is a balanced, line-level input, with a balanced line-level output, and provides gain compression on the order of 10 to 12 dB or so, which is adequate for the intended purpose.

Although the transformers in that unit are essentially telephone-grade, those limiters are in big demand nowadays by the recording guys. Why, I have no idea, as it is far from a high-fidelity unit, but they go for big bucks on e-Bay, etc. I had one a number of years ago, but sold it and never looked back. I'd consider selling it and using the proceeds to buy a much better unit, such as the Inovonics 222, which is superb for tightly controlling the modulation of a typical plate modulated AM rig. You could sell the FAA limiter and probably purchase a brand-new 222 with no cash out of pocket. That is the kind of $$$ those things bring these days.

Good luck with your unit.

73,

Bruce

Thanks Bruce and Todd!

I found it - It's apparently a CA-1589 Regulated Output Amplifier and they ARE worth quite a bit!  I didn't figure it would be all that useful, especially since I also have a Urei BL-40 and an Audimax at my disposal...  :)

See: http://www.gearslutz.com/board/high-end/154093-maxson-dept-commerce-ca-1589-tube-comp-limiter.html

Well, I could always use the $$ for something more fun.  I'll clean her up and list her on eBay. 

Thanks again guys!

73,
Greg

one to two thousand bucks.  It has followed the Astatic JT30 and vintage p.p. tube audio amps into the realm of audiophoolery.   ???

They could probably get the same sound with an equalizer set as a bandpass filter and an old compressor. 

If you can get a grand for it, Bruce is right, you are better off getting a used 222 or CRL PMC 300, 400 or 450 and pocketing the difference.

you can recap it with "hi-fi" electrolytics  ;) and orange drops and maybe get another $500 for it.  Unless the phools think the old ones sound better  ::)