Original EMI-modified Altec compressor on eBay: UPDATE

NOTE: the above unit eventually did sell on eBay for $35,000. See below for scan…

Here’s something that you don’t see everyday. Courtesy of this eBay auction, an apparently original EMI-modified Altec 436B. Buy it now for $55,000 (fifty-five-thousand) US dollars. If this price seems absurd (and it surely is optimistic at best), I will point out that the seller claims (and he/she may very well be correct) that this particular unit was in fact used on numerous Beatles recordings. The particular quality of its compression, pumping, and mild distortion were integral to creating the vocal and drum sounds of the most widely-heard and widely-copied pop/rock recorded sounds in the entire history of sound recording. Add to that likely provenance the fact that only a handful of these units were ever made and you have a very unique piece of audio history on the block.

image source

Here’s a shot of the rear of the unit. A few things worth noting: the JJ multicap (above the blue LCR cap) is of recent manufacture, indicating recent servicing. The lineup of three tubes and only two audio transformers indicates that this unit began its life as a 436(x) compressor, not a 438(x) mic pre/compressor. The mains transformer (far left) was necessarily replaced to facilitate easier use in a 220v country. My biggest question (and please, readers, fill me in… ) is: what is that unit above the 6AL5 tube? Is it a 2nd output transformer to allow of use of a T-pad attenuator on the output while retaining output balance (IE., the T-pad would go between the two transformers)?

image source

Getting back to the front panel, we see evidence of the modifications that EMI made in order to make the 436B more useful in the studio. From left to right: a ‘balance’ push-button switch (not sure what this is, but i image it might have something to do with balancing the vari-mu action of the two halves of the gain-reduction tube? not sure how a pushbutton switch would be implemented there?). Next, a ‘recovery’ or ‘release’ control (self explanatory), then factory ‘input’ attenuator control, and to the right of the meter an output attenuator.

Anyway…those of you who have been following PS dot com for a while will know that I have a tremendous interest in these Altec compressors; I have restored them, modified them, scratch-built them, and use one regularly in the studio. Here’s some links to catch up:

History of the Altec 43(x) compressor and its relation to the EMI RS 124

Adding a balanced output attenuator to an Altec compressor

Modifying an Altec 438a compressor to gain many of the EMI RS124 features

chris

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View Comments

Brian M. says:

12/21/2011 at 4:44 am

I take it you've seen these forum posts, but just in case you haven't, here are links to recent RS124 discussions and schematics:

Old EMI-modded schem (supposedly the real one this time):
http://www.ladislavbrezovnik.com/diy/altec436c/AbbeyRoadStudiosRS124Schematic-D1-2.jpg

Modern schem (in PDF): http://www.dripelectronics.com/media/kunena/attachments/69/EMI_RS124_schematic.pdf

Source: http://www.dripelectronics.com/index.php?option=com_kunena&func=view&catid=12&id=2957&Itemid=41

Original discussion that got Winston O Boogie (aka J. Hinson) to post the schematic.
http://www.groupdiy.com/index.php?topic=41314.0
- chris says:
  
  12/21/2011 at 9:10 am
  
  Hi Brian. thanks for this. No I had not seen this, but I imagined the day would come when these would turn up online... plenty to study in these... thanks! c.
Steve says:

12/22/2011 at 10:11 am

Hey Chris,

I read that since the RS124 was push-pull and would drift over time, causing not only downtime for testing and recalibration, but also the changing of the front-panel settings, that Len Page came up with a brilliant solution. The 'balance' button triggered a blinking neon light which was wired into the audio circuitry - this caused a 'ticking' sound which was sent to both sides of the power amp. If the p/p was correctly setup, the ticking sounds would cancel each other out from phase-cancellation. Next to the balance button is a hole where you could adjust the internal trimpot with a screw driver to recalibrate.

Sounds like a great idea for any p/p amp!

Cheers,
Steve
- chris says:
  
  12/22/2011 at 10:34 am
  
  Hi Steve. thanks for this - the schematics linked below do seem to confirm this. Come to think of it, I recently had a later stromberg-carlson hi-fi tube amp, very advanced for a piece of tube hi-fi, which seems to have had the same feature, although at the time I did not recognize it as such.
  - Steve says:
    
    12/22/2011 at 11:56 am
    
    Yeah, Stromberg-Carlson was some top-end stuff in general apparently. I researched them a bit when i was re-capping a 535-PS console radio I have, which is from around 1940. Very interesting that yours had that same calibration feature as the RS124. So many tricks to know, so little time.
    -Steve
    - chris says:
      
      12/22/2011 at 12:02 pm
      
      so so true... i think that S/C was owned by General Dynamics in the later era... military stuff... like the F-16... i could be wrong...
      - Steve says:
        
        12/22/2011 at 12:20 pm
        
        I didn't know that. Funny, they went from making telephone equipment to audio gear to military stuff. Quite a transitional company!
        
        Talk to u soon-
        Steve
Bafflegab says:

12/23/2011 at 1:40 pm

Usually gear used in Britain stayed 120 volt because in that country 2:1 isolating center tapped isoformers were common. British law specified the use of 110V balanced power for outside electric hand tools with a grounded center tap so that if the tool shorted to the use he would be only zapped with 55-60 volts. So the stepdown transformers were readily available and gave balanced power which quieted things down.

In Germany, this wasn't the case, but they bought little American equipment. The Germans were largely self sufficient, but their stuff never left Europe, because of tariffs and Steven Temmer of Gotham Audio tied their distribution up in the US, What the French, Dutch, Spanish and Scandinavians did would be interesting to know.
Wilson says:

12/07/2013 at 9:09 pm

That little bijou of which you inquire above the 6AL5 looks quite like an old 'heater-oven" for a crystal (inside the oven) oscillator of some type. Hope this helps, Wilson
Tom Fine says:

12/10/2013 at 7:18 pm

$35k will buy a lot of music lessons, and the buyer still won't sound like the Beatles!
Mike Craig says:

02/19/2014 at 6:10 am

Hi Tom,
The unit above above the 6AL5 is a relay, how and what it does is open to speculation.
My guess is its a total bypass relay. We had two of these comps at Chalk Farm studios in 1970 ish. Wish I'd thought of the balance 'tick' idea.. Well not got the experience I've now. BTW EMI bought 3 Chiswick Reach compressors (based on the Altec designs) which Vic Keary (Thermionic Culture) and I designed, because, apparently they were the nearest thing the could get in to the Altecs when re-mixing Beatles stuff. They wouldn't tell us at the time why.. it was a secret project.. "can't tell you"..
Gabriele says:

03/04/2014 at 6:04 am

I remember seeing that auction.
Isn't that the relay to remotely control (footswitch?) the HOLD function of release time? Pretty cool feature!
There's a RS124 thread on groupdiy.com where you can get this bit of info from.
Gabe.
alex says:

08/04/2015 at 1:53 pm

Got the 438c one from Olympic studio owned by Keith Gran...it has recorded beatles rolling stones jimmy hendrix Bowie pink floyd queen t rex elton john etc tec and all absolutly all the most famous bands and artist... if the buyer of this one can contact me i ll be happy to sale same kind of price
alex says:

08/04/2015 at 2:14 pm

plus Eric Clapton, The Eagles, Led Zeppelin, The Who and more
Mark says:

10/17/2016 at 4:15 pm

Hi Chris.

I was wondering if you could help me identify an old Altec tan compressor that has basically the same layout as the back of this unit, but different front knob position and. No ,idle number to be found on the unit. I have had it some Altec mic pre Amps and an old Klein and Hummel tube Eq in storage for some years. Finally dug them out.
- chris says:
  
  10/17/2016 at 6:49 pm
  
  sure email a buncha pix