The AM Forum

Found in a dumpster outside radio station K? in G? Texas.. Rumor there is a 250W Raytheon AM rig in disuse as well, inside, too heavy to move 'yet'. My operatives might be able to negotiate for it.. unknown if exist at this time.

If this RCA BA-6A limiting amp can be resurrected, I might get rid of the silly Marti and the vacuous volumax 400 solid state limiters. This has tubes in it and the coupling caps are old style oil ones (sorry, no silk dielectric..). And DC for the filaments if I am looking at the wires correctly. Could be a nice piece with some care.. Anyone have the schematic? 8-b....

Yes, it just may strap...but, will it blend? That is the question.

http://youtube.com/watch?v=fY8MqWBIHvo (http://youtube.com/watch?v=fY8MqWBIHvo)


Dave Goncalves
W1EUJ

Clean it up, get it working, and a resulting eBay sale could finance whatever audio chain you could possibly want  ;D

Nice find, PJ. The audiophools would be drooling.

250W Raytheon xmtr sounds like the RA-250, like the one N3WWL recently gave away at a fire sale price. Pair of 810s modulated by a pair. These rigs are overbuilt and likely the best quality you will find in BC transmitters, heavy gauge steel double-walled cabinet and all. VERY much worth going after if the situation presents itself. I rescued its big brother, the RA-1000 in 2005 and, despite being heavy and a lot of work (and ending up in someone else's station), feel glad that it was saved.

There aren't a lot of them out there, and they are beautiful rigs despite having no viewing window for the toobs. Copious amounts of chrome, excellent two-tone paint, meters galore.

Grab it!! With both hands, and a few friends. ;)

 

I might be able to rescue the transmitter, but I won't be able to keep it. The brothel is full.. If it is actually there and can be had, I will post back.

I hope the RCA limiting amplifier is repairable. The top of the chassis has some cruddy rust as last night's cleaning attempt revealed.
Not sure how to remove it except with a wire brush. Was there not some chemical that was reputed to dissolve the rust? Naval jelly or something?

Hi Patrick,

Nice find, indeed!

I've had two of these RCA BA-6As. The one I acquired in 1978 from WALK-FM I still have here in the shack, and I just used it the other night on 75M for A-B comparison purposes. It is in pristine condition. Very 1950s looking piece, finished in that RCA umber gray color.

I acquired the other one about two years ago, and the condx sounds similar to the one you just found. It was sitting in the garage of a retired broadcast engineer for a few decades. I cleaned it up as best as I could by just brushing out the accumulated dirt and washing it down. It would be difficult to do a full cosmetic restoration on this unit without fully taking it apart. The only electrical problem with this particular unit was an open screen dropping resistor in the power supply that feeds the screens of the P-P 6V6GT output stage. After replacing that and a few tubes, she sang like a bird.

I did end up selling this grungy-looking BA-6A on e-Bay to finance the acquistion of the Orban 9100A AM processor and some other equipment I now have. Even in the condition that BA-6A was in, it still went for $3600.00 on e-Bay. The recording studio guys pay crazy bucks for these things. Honestly, it is a nice sounding limiter, but it is very much less than ideal for tightly controlling the modulation of a radio transmitter. It is quite slow on the attack time, and peaks will get through that will overmodulate the rig in the negative direction.

IMHO, it would be better to use the bucks from selling the BA-6A and buy something much better suited to the task, such as an Optimod-AM, a Dorrough DAP-310 or DAP-610, or an Inovonics 222, and still have some $$$ left over.

Good luck with you new BA-6A!

73,

Bruce

eh, plug in a d-104 into yer mic jack.  ;)

What's the impedance of a D-104? I suppose I could disconnect it from the Rat Shack TRC-458 "Navajo" CB feed it into the Altec 4-channel mixer. There is that option, and do it the old fashioned way. I don't really have a mike jack yet.

Yes, the limiter would not attack as fast as would be perfect. Looking at its architecture, the detection begins at the plates of the output tubes, so the cat is partway out of the bag before anything happens. I like the design because it uses full wave detection, compared to the old Federal TV Corp. limiter I had before that used half-wave detection. But still the limiting is going to be delayed. If that's its only fault, I'll give it a try. Fixing it will be fun anyway.

pffffhhhh.   :-X Audio chain gangsters. Mellow-toned mafia. Strapper syndication.

Audio empire builders. Quite a message.

....yeaaaaa  VooDoo Audio.... 8)

  Black robed high level  modulation monopoly.  ;D

 ;D

a play on "The Initiation"

If is one without any preamp in the base, you want to work it into a very high impedance - 3 MegOhm or higher. No mixer or ham rig will have such an input impedance, so you will need to modify or build your own hi-Z preamp.

I use 10 megohms in mine, into a 12AX7 pre-amp stage with DC on the filaments.

And here's why.

(http://www.amwindow.org/misc/gif/d104loadresp.gif)

i like potted meat 

I prefer corned beef. I see the D104 has a decent response and a nice pre-emphasis when properly terminated. Maybe an adjustable imedance is in order. Not that I would not prefer a flat response. Nonetheless, the reports using the D-104 with unmodified equipment and no external processing have always beed excellent. I've opened at least one ancient D-104 'can' to find what I could only describe as "moustache dandruff". A secret technology, no doubt. Thanks for the details on the D-104.