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Pro Audio hardware of the early 1950s

The General Electric (GE) BA-5-A Limiter

Continuing our review of the first two years of AUDIO magazine, today we will look at some of the more interesting bits of pro audio kit in evidence during 1954/1955.  AUDIO magazine had just made the transition to its new moniker in the wake of the introduction of the AES Journal (Audio Engineering Society), and for the moment, AUDIO sill covered a bit of the pro audio equipment that would soon largely leave its pages.

The GE BA-5 pictured above is, AFAIK, the largest and most complicated analog audio compressor ever made.  Although it has much less tubes, it’s kinda even more sophisticated than the Fairchild 660/670.    Here’s the schematic if you are interested.  From what i recall,  the BA-5 works by creating an ultra high frequency sidechain to obtain the control voltage value for the compression; I can’t recall the details at the moment but the basic concept was to allow the unit to have huge amounts of compression with very fast timings, but without any pumping or dipping artifacts.  Which was also the intent of the 660/670 design.  If anyone out there has a better explanation of this monster, please chime in.

The General Electric BA-6-B remote amplifer/mixer

The General Electric BA-9-A compressor, a much more basic pro audio compressor.  Circuit is essentially the same as the Gates Sta-Level.  The BA-9 is also known as the the uni-level; schematics are readily available online.

The General Electric BA-1-F plug-in preamp and BA-12-C plug-in power amp

The Hycor 4201 equalizer.  Similar to a Pultec program EQ but without the makeup gain amp; the Hycor is a fully passive device.

Langevin 5116 modular preamp

The full Langevin modular line of 1954: 5116 preamp, 5117 power amp, and 5206, 5208 power supplies

Another remote amp from 1954 – the Magnasync G-924.  Looks very cool.  Magnasync would soon be merged with the Moviola corporation and become a brand name for sound-for-film equipment.  See this previous post for an experiment with the Magnsync URS device.

An early ad (1955) for the Altec 604 duplex loudspeaker.  The 604 would remain a studio-standard recording/mixing monitor speaker well into the 1970s.

Okay this is getting pretty tech-y but here’s an advert announcing some new-ish tubes you might want to consider: the Tung-sol 12AX7 and the 5881 (AKA ruggedized 6L6).   Transistors were on the market at this point (1955) but were a ways off from reaching the performance and reliability that these great tubes offered.

Magnasync Moviola URS as a guitar amp – UPDATE

Magnasync/Moviola was a Los-Angeles based manufacturer of film editing equipment.  They did make a few audio products designed to support the large upright and flatbed Moviola film-editing machines which were their main products.   The most common of these audio-products is the URS 5-watt tube amplifier with built in 4″ AlNiCo speaker.  The URS apparently debuted sometime around 1955.

I recently purchased a pair of these things for a few bucks.  Aside from needing new pilot bulbs and some contact cleaner in the volume pot, they seemed to be working alright.

The rear of the unit (not shown) has a 1/4″ speaker jack (labeled ‘Headphones” which mutes the built in speaker when a cable is inserted.  Other than that, though, there was no obvious input jack.  There is a 4-pin amphenol jack with DC present on 3 of the pins.  the 4th pin is the audio input. Ahh Ok.    There is a also a single-pin DC power connector/takeoff?  Not sure.

Anyhow, kinda irrelevant.  Since no one is going to be using these things with an actual Moviola sound-head, figured I would just make em into lil guitar amps. OK it’s gonna get a little technical here, so pls skip the next paragraph if you wanna just get to the sounds…

Since the tube compliment is 7025 (aka 12AX7) – into 6AQ5 power tube (aka basically lower-voltage rated, small-bottle 6V6) with a single volume pot between the two 7025 stages, this thing is basically…. a tweed fender champ.  Yes, there are some important differences – different plate resistor values, no cathode bypass caps on the preamp stages, and i think some frequency compensation in a the feedback loop?  But basically a tweed champ.  ANYhow…  Following the advice offered here, i put a 1/4″ guitar jack where the single-pin power socket had been.    Then i simply added the other basic components of a Fender guitar-input-stage:  a 1m resistor to ground, and a 68k resistor between the input and the grid of the input tube stage.  Replaced the 2-wire AC cable with a 3-wire grounded cable, and done.

There is plenty of talk on the web about these things…  lotsa folks have converted these to guitar amps in the same manner that i discussed… and people seem to be very happy with them.    Check out this fellow’s work. He did an especially thorough job.  I was personally kinda shocked with the sound that it makes.  Never in my life have i heard so much distortion and fuzz out of an amp.  It really is, pardon my language, fucking insane. Here’s 3 sound clips.  (Gibson Firebird gtr.   SM57 3″ in front of the speaker, into MBox.  ‘Clean’ and ‘Overdrive’ examples have analog echo pedal between the guitar and the amp.  Fuzz is just the amp.  No other eq or processing applied).  Check it…

Clean: Magnasync_URS_clean

Overdrive, fingerpicked: Magnasync_URS_overdriven

Fuzzed out (max volume): Magnasync_URS_fuzz

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UPDATE:  One of the two URS conversions that I built was purchased by producer P.K.  for use on an album project with a new band out of London.  When the record comes out (assuming the URS tracks make the final mix), I’ll post links to the cuts here so that y’all can hear the sound of these fantastic little amps in-context.

Oh and about that other URS conversion that I built: as of today, it is still on-sale at Main Drag Music in Brooklyn NY for a mere $250.  Call or email them if yr interested.