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Connecticut Audio History Pro Audio Archive

Excellent Article on Larry Scully and the Variable-Pitch Lathe c. 1956

Download a six-page article from HIGH FIDELITY 1956 concerning the history of the Scully corporation of Bridgeport Connecticut, including an explanation of the significance of the variable-pitch Scully lathe.

DOWNLOAD: High_Fidelity-5612-Scully_Sm

At left: Larry Scully circa 1956.  Thanks to reader TF for this very interesting piece.  As I have mentioned before, I drive by the old Scully factory nearly every day on my way to work at Gold Coast Recorders.  I had been hoping to uncover some history of this once-great Bridgeport institution and this article certainly sheds some light.  Some interesting bits from the article: in the 30s, Scully briefly ventured into the manufacture of P.A. equipment.  And beer coolers.  Also of note: the price of a Scully lathe in today’s dollars?  $72,000.

Previous Scully Coverage on P S dot com:

The Plant

The Model 601 Lathe

Some very neglected Scully 280s

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Uncategorized

Three interesting Hi Fi Amps circa 1948

Download a three-page article from the September 1948 issue of RADIO ELECTRONICS on the subject of ‘Three Straightforward Amplifiers.”  Author is John Straede.  Schematics ETC are all included in the download.

DOWNLOAD: Three1948Amps

Above, the most interesting of the bunch: a single-ended 6L6 amp which uses fixed bias for the output stage.  I have never seen a fixed-bias SE power amp.  Seems like this could yield some unique overdriven textures for guitar applications.  Worth a look.

Above, the 13-watt 6V6 PP unit.  A couple of things to note: the input stage uses a 6U6 pentode.  I have never come across a 6U6.  Anyone use one of these?  Also: the 6U6 stage uses ‘Grid Leak Bias,’ in which the cathode is at ground potential and yet no DC bias is used on the grid.  I have never tried this type of bias.  Anyone?  Is it worth trying? What are the benefits/liabilities of grid-leak bias?

 

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Uncategorized

MXL R40 Ribbon Mics are back for $69.99 at M F dot com

I continue to get a lot of readers here drawn to my earlier post on the MXL R40 ribbon mic.  Click here to read that earlier post.  In that article I describe replacing the stock transformer with an inexpensive Edcor unit and getting very good results.  Anyhow, shortly after i wrote that piece, the price of the MXL R40 shot up dramatically – to around $120.  Well I guess they couldn’t move ’em, cos they are back for $69.99.  A great deal IMO.  Click here to pick one up.

Categories
Technical

1961: Five Things

From the 1961 Langevin Catalog, which unfortunately I cannot upload due to massive file size.  Anyone know of a reliable, free way to reduce PDF size?

 

 

 

 

Categories
Altec Technical

Novel Vacuum Tube / Diode Compressor: 1950

Download a short piece from RADIO-ELECTRONICS, 1950, on the subject of a DIY audio-compressor:

DOWNLOAD: DiodeCompressor1950

This promises to be an interesting unit.  It’s designed (like a Shure Level-Loc) for Mic-Level-In, Mic-Level-Out, but that could pretty easily be changed for balanced-line operation by omitting the first 12AT7 stage and using a modest step-up transformer (maybe 1:3 or 1:5) going into the input level pot, and then adding another output stage and output transformer.  (Since 1/2 of the 2nd AT7 is unused, I am thinking: eliminate one of the 12AT7s entirely, build this circuit minus the first stage using one 12AT7, and then add the output stage from the Altec 1566).  The unit promises to add distortion, and there is some sort of low-pass network before the 3rd grid that will also need some sort of variable components added in order to control the quality of that distortion.  My biggest question, though: will plain ‘ole IN4007 Diodes work in the circuit?  I plan to build this thing soon and all questions will be answered… always looking for new (old) sources of novel grit+crunch….

Categories
Technical

DIY Remote Broadcast Mic Preamp c. 1950

Download a four-page piece from RADIO ELECTRONICS, March 1950, on the subject of Build Your Own Two-Channel Remote Amp.  Author is Richard Finkbeiner.

DOWNLOAD: RemotePreAmp1950

Again with those T-pads.  Anyhow, we have here two 6J7 pentode stages in series supplying a 6F6 (v v similar to a 6V6) output stage.  Here’s the schematic:

The schematic is a bit opaque due to the fact that this piece is designed, ‘at the touch of switch,’ to become a cue amp – to receive signal, via its Station-Link, rather than send signal.  Confused?  The article will make it clear.  Anyhow, if anyone has tons of time on their hands, it might be interesting to re-draw this schematic minus all of that circuitry.  I would be v curious to know exactly which output transformer the designer used: a 5K to 600 ohm transformer that can handle 3 watts of DC and remains flat 30hz – 15khz?  Sign me up.  (It sure looks like a Langevin, but as I don’t have the early 50s Langevin catalogs, I can’t say which model it might be)  I can tell you that even the modern Lundahl that I use in my BRDCTR can’t offer quite that level of performance, although Lundahl does promise it…

Also of note to all you builders out there:  the author observed a full 15 db less overall noise with a 1620 in the input position relative to a 6J7 in same.  I wonder for how much longer we’ll be able to easily buy NOS 1620s…

 

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Uncategorized

Fill In The Blanks

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1.__________________

2.__________________

3.__________________

4.__________________

5.__________________

Use the comments section to weigh in.  ‘Correct Answers’ circa 1961 to follow next week.

Categories
Technical

Audio Mixing Console Circa 1949

Download a three-page article from RADIO ELECTRONICS, Feb 1949, on the subject of Build Your Own Audio Control Console.  Author is Richard Dorf.

DOWNLOAD: AudioConsole1949

Kinda a wacky design: it’s intended for mixing four low-z unbalanced sources, using multiple T-pads summing through a resistor network to a single tube grid (rather than using multiple input transformers and multiple tubes).  Not really so practical. I’m posting this primarily in the hope that one of my readers can elucidate the output stage design for me.  It seems like it must be an error, but maybe not?

The article states that ‘any plate to line output transformer can be used,’ which means that the design does not specify an air-gapped (DC-handling) transformer.  Not sure how that applies to this design.  Seems like the DC would be quite different on either side of that 33k resistor?  Also not sure how any signal would develop there? Is it possible because on of the secondary legs is terminated to ground?  Confused.  Were there any commercially-manufactured pro-audio units that used this kind of line output stage?

Categories
Synthesizers Technical

1951: The Thyratone, a DIY Vacuum-Tube Monophonic Keyboard Synth

Download a ten-page pair of articles from RADIO ELECTRONICS, 1951, on the subject of building your own keyboard synth.  Author Richard H. Dorf.

DOWNLOAD: ThyratoneSynth1951

This has got to be one of the most insane DIY projects I have encountered from the era.   You would have to be a really ambitious MF’r to try and crack this one.  Also, and perhaps this goes without saying, it was very ahead of its time.   The Thyratone predates the appearance of the Musitron (AFAIK, the first synth to be used on a pop hit) by eight years. Many now-accepted synthesizer features, such as variable attack and decay, are fixed in the this circuit so as to more closely create the sound of a conventional organ, but since everything in the article is more or less explained, it seems certainly possible to make these aspects player-adjustable.

Anyone ever tried building a keyboard-playable, all-tube synthesizer?  Success?

 

Categories
History Technical

Prepare For A Journey Thru Time And Space (*special soldering-iron edition)

How are y’all doin.  Sorry I’ve been away for so long; it’s been real busy ’round here, and like my Pops always says, you gotta make hay while the sun shines.  But… there’s only so farming you can do without yr back giving out, so I’m taking a little break to re-stock Ye Ole Country Store (aka Blog) with piles of new stuff.  Been a good coupla weeks at the flea market, annoying camera-crews aside (see my Tumblr for details).  Recently picked up a very large collection of circa 1950 DIY Electronics publications, and I’ve culled the cream-of-the-crop for y’all: some still-useful audio projects, and lots of interesting but forgotten bits and bobs from the pre-transistor era.  Schematics and project notes on some unique amplifiers, preamps, and even a novel compressor design that promises some unique sounds.  I’ll be posting a dozen or so of these pieces over the next couple of weeks; in the meantime, here’s a quick visual sampler of what yr in for.