**update 07.09.21 – audio clip added! see below! you can now HEAR this monstrosity!**

Download a 4PP article (+advert) from the June 1951 RADIO ELECTRONICS on the subject of a novel (+fairly creepy) electro-mechanical speech-synthesizer designed by Bell Labs.

This has got to be one of the wildest electro-mechanical synths every created. I wonder what New Jersey basement it ended up in. I’m preeeeetty sure that this abomination provided the historical-basis for the device that Tony Shaloub’s character was developing in the first season of The Marvelous Mrs. Maisel. Anyhow. It’s weird and far-out and I think you will enjoy reading about it.

T.F. provided us with this audio clip so that you can hear this device in action. it’s pretty remarkable TBH…

DOWNLOAD: LarryScully_BertWhyte_Interview_AUDIO_1169

As longtime PS dot com readers know, we are based in Bridgeport CT,  former home of Scully.  Scully was America’s leading manufacturer of Lathes for cutting LP masters; only Neumann lathes offered any real competition in terms of quality. Starting in 1962, with the aid of former PRESTO engineers, Scully also began manufacturing high-quality tape machines in a variety of formats.  I had a Scully 1″ 8-track machine recently and it was a marvel of engineering; the sound quality was absolutely astonishing.  In this article, L Scully describes his father’s start at Columbia Records (also based in Bridgeport in the early 20th century), their movement the manufacture of professional tape machines, ETC.   Great piece of history.

There is a plethora of Scully, Columbia/Bridgeport, and Bert Whyte material elsewhere on this site; just use the search box. 

DOWNLOAD: Microphones and their placement

Written by Arthur Davis, Phillip Erhorn, and their team at Aerovox, the article offers an interesting historical perspective on microphone technique in the 1950s.

(image source)

If you’ve spent much time creeping around inside old electronic equipment, you have undoubtedly seen numerous examples of the capacitor shown above.  I really don’t have a super-strong sense of ‘how good’ Aerovox caps were as compared to their contemporaries, IE., how often they tend to need replacement, ETC,, but IIRC they tend to be more reliable than most 50’s foil caps.

“The Aerovox Research Worker” was a sort of ‘branded content’ marketing item that the company published from at least 1949 through 1958.  I recently picked up a large pile of these publications, and most focus on RF and TV applications.  This was the only one I could find that was audio-focused.  Enjoy. CR

image source

A quick google search suggests that there are thought to be only 5 Fairchild 627 equalizers in existence.  One seems to have sold on eBay recently in the $7000 region.  The 627 is a line-level EQ with continuously variable low and high bell boost sections as well as high and low roll offs. Unlike a Pultec, though, it is an active EQ, and it uses some pretty unusual circuitry – especially the high-cut section, which I don’t comprehend at all.

One point to note: T2 should be wired to reverse phase.  I was v excited to find this schematic, because it seems like a pretty easy piece to build – there is no mention of the proper B+ voltage, but 250 is generally a safe bet; there are no weird inductors (the UTC S-23 plate-load choke is an off-the shelf part, so we know its specs  -5000ohm DC, 300 henries); the audio transformers don’t need to handle DC and the turns ratios are spec’d:  BUT:  But.  Those triple-ganged pots.  WTF do we do about them?

Can anyone crack this case? Any insights, pls let us know in the comments section.

On the plus-side:  at very minimum, this schematic does reveal an excellent and easy way to implement a 6E5 seeing-eye tube simply paralleled to a grid in the audio path.  So at very least, now i know how to use those v excellent things in my mic preamps.  Way more evil than a VU meter.

Also: the 6SN7 output section is a neat little self-contained module; def worth trying it with a Hammond 156C choke and an Edcor 15K:600 1/2 watt.   The 156C is the closest modern part to the S23 spec; it is rated 150h and 3.7K ohm, seems close enough?  I used onna these on a hunch in my OP6-semi-clone and it worked just fine in that application, so I am guessing it may work fine here as well. 

DOWNLOAD: Fisher_PR6_Manual

Above: Williamson style amp and power supply.

Fifteen-watt “Alta Fidelidad” amplifier.

Full-featured mono preamp

Super basic hi-z mic mixer

]]> https://www.preservationsound.com/argentine-hi-fi-diy-circa-1958/feed/ 0 https://www.preservationsound.com/the-fairchild-model-605-stereo-tube-phono-preamp-c-1959/ https://www.preservationsound.com/the-fairchild-model-605-stereo-tube-phono-preamp-c-1959/#comments Tue, 03 Mar 2015 15:53:50 +0000 http://www.preservationsound.com/?p=8323 How y’all  doing on this frigid day in March,,,  so listen, srry abt not posting much new material this past year.  I’ll be frank: as phones keep getting better and better, and online content keeps getting more and more tailored TO the phone as a consequence thereof, many of us are spending less and less recreational time in front of the laptop (although I am still planted in front of some sort of Mac, invariably, for my production and composing work,,,) and more of that ‘leisure’ time with the phone.  Instagram rather than ‘scoping blogs’ seems better tailored to how most folks are spending their recreational internet time these days.  So we’ve been keeping an active+vigorous presence up there.  This blog isn’t going away, but do check out the IG account if you have not yet.

Ok NEways,,, I was diggin thru the archive for something today and I came across the schematic for a phono preamp that Fairchild offered around 1959 – their model 605.  Strangely enough, their prototype (image at head) was labeled ‘606.’  Production examples do bear the mark 605, though, as this example from a Russian website indicates:

(image source)

There is very little information on the web about this unit – in fact, a google search offers,,, good ‘ole Preservation Sound Dot Com as its first result when queried.  And not much else of relevance.  We apparently ran an advert for this very unit some years back (click here for that earlier post).  So I was very excited to see that this unit, which is VERY buildable using off-the-shelf components, had not yet ‘migrated’ onto the web.  The Fairchild 606 offers both MC and MM input stages, 600ohm balanced outputs, and selectable EQ curves and stereo or true mono LP operation.  Now, I’ve built many Marantz and RCA-style tube phono preamps to great success, but this Fairchild is simultaneously exotic AND obtainable enough to be quite intriguing.   So, DIYers of the world, here ya go:  knock yrself out:

(click on image for a (huge) full size image)

There’s nothing exotic in it: no custom inductors, weird-taper pots, or un-source-able transformers.  The toughest thing to find might be the 4P/6T switch, but you could always sub in a pair of 2P/6T switches and just use two hands.  In fact, the input transformers, which I can confirm are 1:20 from the 600 ohm tap, appear to be garden-variety Beyers:

(image source)

Regardless, though, you can use any hi-fidelity input transformer with a roughly 1:20 ratio and an input impedance approx.  10X whatever the output impedance of your moving-coil cartridge is.  And if you only use a moving-magnet cartridge, you can skip that part of the circuit entirely and just build the 47K ohm grid-input stage (and all that follows).  As the schematic indicates and the images confirm, this product was built in two chassis:  (preamps+EQs) and (power supply+output stages).  Other details: R109 and R209 are level controls, basic voltage dividers with a 20db range.  EQ offered is flat, RIAA, or RIAA plus add’l roll-off, and the ‘Lateral’ switching positions offered cancel out the vertical tracking information, resulting in the cleanest possible sound from mono records.  The output stage is fairly conventional, but interestingly enough requires single-ended transformers, so you will be rather limited in your options here (a 15K:600 that can handle 8ma DC unbalanced, such as a UTC A25, should work fine).

This is a fairly advanced project, which I have personally not built (yet). I cannot offer any technical support or help with this.  If you have never built a vacuum-tube phono preamp or mic preamp from scratch before, I would not advise undertaking this project.  Good luck, and if you build one, send us some pics!

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. 

Here’s what SK has to say about the Ikegami-Tushin Limiter:

‘(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…’*************

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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

DOWNLOAD THE COMPLETE ARTICLE: 1954 Audio Mixer

There’s nothing terribly interesting about this particular circuit other than the output stage, which is push-pull and and is driven by a 3:1 interstage transformer which functions as both a phase inverter and provides a bit of additional voltage gain.

I’ve never made a mic pre with a transformer phase inverter, but it could be very cool.  At Gold Coast Recorders one of the engineers’ favorite mic pre’s is a custom unit that I built based around an RCA 9362 cinema line amp (see earlier article here).  The 9362 is a push-pull output module, and it’s definitely a different sound – almost every tube mic pre made is single-ended.  Anyhow, at some point I will def build the circuit above into a mic pre.  Probably as soon as I find a pair of appropriate hi-fidelity (and shielded!) transformers for a buck.