In May of 1962 “AUDIO” magazine celebrated its 15th anniversary. IIRC, AUDIO was the more consumer-facing half of what had initially been AUDIO ENGINEERING magazine; the AES Journal being created sometime in the 50s to carry the more professional articles. Anyhow, for their 15th, AUDIO asked some of the experts of the time to weigh in on THE FUTURE OF AUDIO. Harry Olson, certainly one of the greatest inventors of sound equipment who ever lived, had some comments that struck me as being incredibly prescient. I’ve never seen this reproduced anywhere, so check it out, enjoy it, share it, and take a minute to speculate on where this is all going.
SK has been so kind as to provide the schematic for this obscure device, as well as some background information. I am posting the schematic full-size, so you can control-click it and download it for detailed viewing.
The photos in this post come from this Japanese auction website; the device pictured here recently sold for just Y30,000 ($300 USD). And in working condition.
‘(It is) very much inspired by the RCA BA6A for sure. It even looks a bit like it. The tube format is very similar: just change 6sk7 to 6ba6, 6j7 to 6au6 those goes into 6v6 PP and transformers between 6au6. 6ba6 were popular and cheap in japan because we made those a lot in japan in the 1950s and 60s.
6sk7 and 6j7 were never made in japan. This unit also has an extra gain stage before first stage, which is pretty neat. The components seem very high-end and some are custom made for this. When i was gathering info about the ba6a in old tube shop, an older ham radio guy told me that he DIY’d one of these a long time ago…’*************
SK also recently built his own BA6A from scratch. It is depicted above, and you can hear audio samples of it at his soundcloud page. SK has also scratch-built the Federal AM864 tube limiter, and he has this to say about the projects:
“The sound you will hear in soundcloud is a good comparison with the fed864. The fed has good high open but compressed sound, the ba6a has low mid, ton of low mid. I love them both. The first time I used them was at a studio in Chicago back in 90s when I was living in US. At that time I was using LA-2A mainly, but that studio had a Fed864 and BA6A. They blew my mind, and since then I wanted them so bad!’
SK also provided some build-notes on his BA6A project; if you are planning on building you own BA6A, you might find these useful: S_Komiya_RCA_Ba6a_DIY_notes
Years ago I ‘lunchboxed’ one of those above-depicted RCA BE100 equalizer modules. The RCA 100 series of the early 70s was the end-of-the-line for RCA’s pro audio gear. The series consisted of the MI-141651 op amp, the BMM-100 Mixer (channel strip, aka MI-141550), BE-100 EQ (aka MI0141560), BA-101 and BA-103 preamps (also designated as MI-141501, MI-141503), BMM-110 Submaster module (aka MI-141570), and BIM-100 Isomix amplifier (aka MI-141520).
Since I seem to be one of the few fools who has publicly admitted to spending time messing around with these things, I’ve gotten several requests over the years for the accompanying data and schematics. Well guess what. TIME HAS COME TODAY. Download all of the tech date for all of these modules.
I’d never been particularly interested in learning solid state electronics. There just didn’t seem much point; considering that you can buy a 4-channel Sytek mic preamp for $900, there just ain’t much to motivate anyone to DIY ss kit. Tube stuff is another matter – it’s a different sound, and well-made ‘real’ high-plate-voltage, transformer i/0 tube gear is super-expensive. So I learned to make the tube gear both for my own studio and as a way to make some add’l income by custom-building for other engineers.
All that being said, there is an undeniable appeal to be able to build something useful that doesn’t require a heater circuit and the attendant 60-cycle-hum battles that come from those hi-current windings. Solid state is just easier, which is prolly why it has won-out in the world of consumer electronics, if not necessarily in the pro-audio world. In my endless diggin for ancient tubes and transformers and bakelite meters I invariably come across stashes of ole germanium and silicon transistors, and I recently decided to take the plunge and try and cross this bridge once and for all. Cos I can talk tubes and tube audio circuits up+down, but frankly I don’t know shit abt solid-state and maybe it’s time I learned.
DOWNLOAD THREE CIRCUITS FROM RCA HM-80:RCA_SS_Hobby_1968
The old RCA Tube Manuals have always been my primary source of information for my tube-audio builds and experiments. The circuits that they recommend are the most solid, reliable, and practical that you will ever find. I trust them implicitly. And why not? After all, this was the company that made the tubes themselves! So when I decided to try and get into SS, I started with the RCA Solid-State Hobby Circuits Manual. In the scan above you will find a mic preamp, a line-level compressor, and a fuzz pedal. I’ll be building all three eventually and I will LYK how it goes. In the meantime, if any of y’all beat me to it, drop us a line and report back,,,
Not to be confused with the RCA BK-4 “Starmaker” hand-held ribbon mic of the 1950s, these later Starmakers were cheap prosumer and consumer units. Models on offer included the Starmaker 96, 97, 98, 101, 99, and 100. The top-of-the-range 96 has decent specs and useful features; gonna keep an eye out for that one.
Earlier this year we ran a piece regarding the c. 1952 RCA BC-2 broadcast console. T.F. has also provided us with a subsequent scan from AE mag, 1953, which highlights the companion BCM-1A “extender” console, designed to add an additional 12 microphone inputs (4 accessible at once) to the 2B.
Click below to DL the article by one George Singer.
Today on PS dot come: a short but v v informative piece from BROADCAST ENGINEERING , July 1963, which gives specs for nearly all of the broadcast compressors that were available that year. Models covered include: Collins 26J Auto-level, Collins 356E, Fairchild 666A, 666, and 663; Gates M-5167 Sta-Level, GE BA-9 Uni-levele, ITA AGC-1A, Langevin AM-5301 Leveline, Quindar QCA-2, and the RCA BA-25A
UPDATE: T. Fine was so kind as to provide the entire 3-part article as a compact PDF. click here to download it: BrdctEngnrgAudioLeveling_1963
Above: RCA 77, BK1, BK5, and a slew of others, all referred to by their ‘alternate’ MA-designations: the MA-2311, 2313, 2314, 2315, 2316, 2317, 2318, and 2319. Can someone tell us why RCA used standard model names, MA designations, and MI designations? Was it so they could charge certain customers more money for the same products?
So true. What more DO you need in a mic? The RCA BK-5 is one of my all-time favs. No other ribbon mic sounds remotely like it. If you dig ribbon mics, save up for one of these. You will not be disappointed. Especially if you need to tame a sibilant vocal while retaining an overall ‘bright’ and forward sound. Also killer on piano, guitar amps, and probably everything else, actually…
LEFT: The BC-2B incorporated the RCA MA-11241 dual mic pre-amp unit; a two-stage circuit, each channel used a single 12AY7 for, I would suppose, about 25 – 30 db of gain. The schem for the 11241 is posted below here. Notice that, similar to the earlier octal-pentode based RCA mic pres, the full B+ current flows through the output transformer; this severely limits your choice of output transformer: the only vintage full-fidelity units that I am aware of are the UTC A-25 and LS-27. Lundahl makes a modern unit that satisfies this spec, as does Hashimoto (HL-20K-6); very expensive pieces tho! Any of you fellas know of other 15k:600 1/2 watt transformers that handle 8ma unbalanced DC and still pass 40 – 20K?
Here’s a dude that’s cloning the BC2B preamp; price is $650 for the preamp plus another $450 for the power supply. Assuming that the build-quality is good, $1100 is a pretty fair price for this thing; I know how much those Lundahls cost ( I use the same O/T in my BRDCSTR as well) plus phantom power is a pain in the ass to build in.