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?
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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….
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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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Fill In The Blanks
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Use the comments section to weigh in. ‘Correct Answers’ circa 1961 to follow next week.
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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?
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?
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.
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Sank Comes Thru Again
Wanna take a second here to say “thanks” to Stephen Sank, again, for his sagacity in the service of my old ribbon mics. My circa 195X RCA BK5b is one of the most popular (with vocalists) in my pile/collection of mics and it gets used a lot on sessions… and it breaks every couple of years. Pretty consistently. Luckily there’s a reliable, experienced, and reasonably-priced serviceman who really knows his way around these dusty old gems. I was afraid that the ribbon had broken and/or fried, yet again, but that was not the case. From S:
“Very bizarre problem, very easily dealt with. I have never, ever seen it happen before on an RCA, but one of the transformer taps went bad spontaneously. Wire up into the potted transformer shield casing is fine, so it happened in the core. Fortunately, the 150ohm tap is fine, so just moved a wire to it. Works great, ribbon still perfect. And there is no reason at all to suspect any future transformer issues. And that transformer is unbeatable & unobtainable, so don’t even ask.;-)”
Yeah it never would have occurred to me to suspect the transformer. Anyhow my BK5b is back and should make another recorded appearance soon. You can find Sank at this website.
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DONT TOUCH
DONT TOUCH
MY MIC
IF YOU WANNA SING SOME BGVS
FINE, GIT YR OWN GODDAMN MIC
THE BOX STAYS LOCKED WHEN REH IS OVER
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Fairly high-up on the list of ‘unnecessary shit that i prolly shouldn’t have bought‘ is this mint-condition Peavey PVM-38 microphone. But what an incredible artifact, innit. Consider what kind of paranoid, uptight culture could have created a shitty low-cost microphone that includes a military-grade locking hard-shell case, thus allowing access to only the key-holder. Exactly who/what is this case designed to protect/prevent? If you are concerned about the sanctity of your microphone, perhaps simply take it with you? It is not so large/heavy as to preclude easy transport? Rather, I feel like what we have here is the superimposition of two previously unrelated concepts: the microphone, on one hand, and an intense concern with property rights on the other.
I can’t tell you from whence this artifact originates, as there is little information online concerning its heritage, but Peavey Corp does offer this download (PVM_38i) regarding a very similar model; the date of that document is 1993. I can vaguely recall seeing these mics for sale at the local mom+pop when I was a kid; late 80s, early 90s; and the box made a strong impression: at least to a child, the effect was ‘wow that must be a rad mic if such intense security surrounds it at all moments.’ The semantic chain here is the ever popular Security/indicates/Economic Value/indicates/Quality. But then what happens when one learns that the object in fact has a low cost, as these mics no doubt did? Do we still make an easy leap from Security to Quality? Oh Peavey. The mysteries you hold.
While the precise semiotic operation of the Peavey PVM38 and its associated flotsam (IE,, case+key) may remain a subject of debate, we can fairly readily assess the object’s quality. Yup it’s time for yet another SHURE SM57 vs SOME UNPOPULAR OLD MIC test. Here’s a single acoustic fingerpicked guitar performance; mics are positioned as shown above; levels are matched exactly. No processing whatsoever was applied, other than digitally increasing the levels to full level. The Peavey’s output is approximately 2.5 db hotter than the SM57. Take a listen:
First, the SM57: ShureSM57_ref
..and now the PVM38: Peavey_PVM38
My $0.02: The sound is pretty similar. The Peavey seems to have less boxiness/low mids, a pretty similar pickup pattern, and a little less accuracy/detail in the very high end. Overall it has a bit of that ‘budget mic’ sound but the high output is a plus. I would imagine that the PVM38 would probably make a decent live vocal mic for rock vocals, and probably good for under-snare as well. Certainly worth the $15 that I paid.
Download a nine-page piece first presented in 1952 by one Otto Bixler of the Magnecord Corporation. Bixler describes Magnecord’s early work in the field of stereophonic recording and reproduction.
DOWNLOAD: BinauralRecordingSystem_Bixler
Thank you to a very helpful long-time contributor for sending this piece in. This article was originally published right at the dawn on the stereo era, and it’s interesting to read some early speculation about the promise/usefulness that stereo sound offered. I’ve been thinking quite a bit about stereo effects recently, as I picked up a Calrec Soundfield Mark IV earlier this season. It’s currently being serviced, but look forward to some interesting experiments and reports on that exotic piece soon.
