Category Archives: Technical

DIY Grammafoon Versterker circa 1939

Radio_expres_magazine_NetherlandsWe’ve covered some fairly obscure + forgotten audio publications here at PS dot com, but this one takes the taart. RADIO EXPRES was a Nederlands DIY radio/audio magazine published from 1932 through 1939, and perhaps longer.   Well, it was certainly published for the entire year 1939 (22) issues, since I’ve ended up with that pile of them here.  As is typical of ‘radio’ publications in the pre hi-fidelity era, the emphasis is much more on RF than AF, but I still managed to find a few interesting articles of possible use to y’all audio-folk.  First off:  this cute lil 4-watt Grammafoon Versterker (that’s a phonograph amplifier, btw):



The ‘Lampen,’ or ‘tubes’ used are an E99 high-gain triode input stage and an AL5 pentode output tube.  Interestingly, these are both 4V filament tubes.  The 4V filament is not seen in any US-manufacture audio tubes that I have ever come across.

Versterker_partsListThe article, penned by one J. L. Leistra, spans two issues of Radio Expres and it is very thorough.  It covers all of the theory involved in developing the circuit, and the second part gets into some pretty extensive detail regarding the feedback-based compensation filter.  It wraps up with fabrication, layout, and wiring instruction.  It’s all written in Dutch, btw.

Versterker_Tagboard Versterker_Chassis*************



EL5_schemThe only other really interesting audio-bit that I could discern was this 3pp exposition of the then- ‘neu’ Phillips EL5 (incorrectly indicated as an ‘FL5’ in the above image) 18-watt output pentode.  The EL5 seems like a tube worth exploring; it’s a high-power, 6.3v filamant audio output tube designed to run ona pretty low plate voltage (250- 275) for such a high powered tube.  Could be useful in some situations.  Anyone using EL5s?  Here’s the whole article for you to…. look at. (unless you read Dutch, of course).


I’ll leave off with a quick survey of the best part of this run of magazines: the incredible, world-envied graphic design that the Nederlands is still renowned for almost a century later.  Enjoy – c.

MastheadStoetsRadio Frequenta Bell_Telephone_Holland Sondisko Kristal_Microfoon ThermionLampen

Less But Better: The Braun TG-1000 Tape Recorder of 1970

Braun_TG_1000_!972_picIt’s very hard to find vintage BRAUN hi-fi gear in the states; i’ve seen some amazing BRAUN receivers in Canada, but they either were not sold here, or poorly distributed, because they just ain’t around.  Sporting a design aesthetic that would be popularized in the NAD, ADS,  and PROTON lines of the 80s, BRAUN kit owed it’s beautiful, so-far-ahead-of-its-time character to Dieter Rams.  Rams put his stamp on a huge range of goods for BRAUN; I once found a Rams-designed mini desk fan (!) that was shockingly valuable as a collectors item.  Anyhow, here’s a great synopsis of the career of a man who’s ideal could be summed up as Less But Better:  CLICK HERE.


Via Wikipedia, here are Rams’ ten principles off good design.  Enjoy.

  1. Is innovative – The possibilities for progression are not, by any means, exhausted. Technological development is always offering new opportunities for original designs. But imaginative design always develops in tandem with improving technology, and can never be an end in itself.
  2. Makes a product useful – A product is bought to be used. It has to satisfy not only functional, but also psychological and aesthetic criteria. Good design emphasizes the usefulness of a product whilst disregarding anything that could detract from it.
  3. Is aesthetic – The aesthetic quality of a product is integral to its usefulness because products are used every day and have an effect on people and their well-being. Only well-executed objects can be beautiful.
  4. Makes a product understandable – It clarifies the product’s structure. Better still, it can make the product clearly express its function by making use of the user’s intuition. At best, it is self-explanatory.
  5. Is unobtrusive – Products fulfilling a purpose are like tools. They are neither decorative objects nor works of art. Their design should therefore be both neutral and restrained, to leave room for the user’s self-expression.
  6. Is honest – It does not make a product appear more innovative, powerful or valuable than it really is. It does not attempt to manipulate the consumer with promises that cannot be kept.
  7. Is long-lasting – It avoids being fashionable and therefore never appears antiquated. Unlike fashionable design, it lasts many years – even in today’s throwaway society.
  8. Is thorough down to the last detail – Nothing must be arbitrary or left to chance. Care and accuracy in the design process show respect towards the consumer.
  9. Is environmentally friendly – Design makes an important contribution to the preservation of the environment. It conserves resources and minimizes physical and visual pollution throughout the lifecycle of the product.
  10. Is as little design as possible – Less, but better – because it concentrates on the essential aspects, and the products are not burdened with non-essentials. Back to purity, back to simplicity.

RCA Solid State Audio Projects c. 1968

RCA_1968I’d never been particularly interested in learning solid state electronics.  There just didn’t seem much point; considering that you can buy a 4-channel Sytek mic preamp for $900, there just ain’t much to motivate anyone to DIY ss kit.  Tube stuff is another matter – it’s a different sound, and well-made ‘real’ high-plate-voltage, transformer i/0 tube gear is super-expensive.  So I learned to make the tube gear both for my own studio and as a way to make some add’l income by custom-building for other engineers.

All that being said, there is an undeniable appeal to be able to build something useful that doesn’t require a heater circuit and the attendant 60-cycle-hum battles that come from those hi-current windings.  Solid state is just easier, which is prolly why it has won-out in the world of consumer electronics, if not necessarily in the pro-audio world.  In my endless diggin for ancient tubes and transformers and bakelite meters I invariably come across stashes of ole germanium and silicon transistors, and I recently decided to take the plunge and try and cross this bridge once and for all.  Cos I can talk tubes and tube audio circuits up+down, but frankly I don’t know shit abt solid-state and maybe it’s time I learned.


The old RCA Tube Manuals have always been my primary source of information for my tube-audio builds and experiments.  The circuits that they recommend are the most solid, reliable, and practical that you will ever find.  I trust them implicitly.  And why not?  After all, this was the company that made the tubes themselves!  So when I decided to try and get into SS, I started with the RCA Solid-State Hobby Circuits Manual.  In the scan above you will find a mic preamp, a line-level compressor, and a fuzz pedal.  I’ll be building all three eventually and I will LYK how it goes.  In the meantime, if any of y’all beat me to it, drop us a line and report back,,,

RCA_SS_MicPre_Schem RCA_FuzzBox_1968_schematic RCA_SS_Comp_1968



Federal AM-864 Limiter Clone: Build Notes: update 1


Note: I performed extensive frequency, level, and actual studio tests on the 864 clone today, and several interesting details were revealed.  Text has been edited to reflect that. 

From 1954 through at least 1963, the Federal Television Corporation built an audio limiter called the AM 864/u for the US Air Force and US Army.  The 864 is a simple, rugged device that accepts 600 ohm balanced or unbalanced line-level signal, offers a single front-panel input-attenuator control, and compresses the output level at a 10-to-1 ratio once the threshold point is reached.  The output is also 600-ohm balanced or unbalanced, and it offers a maximum 36db of gain.  The rear panel of the unit displayed the threshold and ratio controls, although these are confusingly referred to as (respectively) CURRENT and THRESHOLD in the manual and schematic.  Attack and release times are fixed, and the manual indicates them at .05″ and 2″ respectively.

AM864_hookupAs you can see in the diagram above, the 864 was intended to be used as what we call a ‘broadcast limiter’ – the final step in the signal chain before the broadcast transmitter.

Download the original 1963 manual for the AM864 (apologies to whomever did the epic work of scanning this 55pp document; I have long forgotten where I got this file from)

DOWNLOAD: Federal-AM-864-U-Manual copy

Federal_AM864_on_benchAfter having scratch-built an Altec 436 compressor years ago, I wanted to try building an 864.  The circuits are very similar, although the 864 uses the older 1940s-era octal tubes and uses a feedback circuit from the plates of the input tubes (rather than the output tubes, as in the 436) for its compression control signal.  More importantly, though, the 436 remains a bit of an oddball underdog in the vintage-compressor market while the 864 enjoys a very strong reputation.  Anyhow, like the 436, the parts cost to build one of these things is negligible, so I figured what the hell.

This is going to be a very long + detailed +technical article, so I’m going to ask y’all to please click the link below if you dare to READ-ON,,,,

Continue reading Federal AM-864 Limiter Clone: Build Notes: update 1

Mullard “Made For Music” c.1960 Catalog / Datasheets

Mullard_1Download the complete 6pp Mullard “Made for Music  / Valves For Audio Equipment” c. 1960 catalog:

DOWNLOAD: Mullard_Made_For_Music

Products covered, with text, specs, and photos, include: Mullard EF86 (6267) pentode, Mullard ECC83, ECC81, and ECC81 twin triodes (12AX7, 12AT7, 12AU7), EL84 (6BQ5), EL34 (6CA7), and EL37 (6L6) power tubes, and EZ80, EZ81, and GZ34 rectifier tubes (6V4, 6CA4, 5AR4).

There’s plenty of info here, operating points, some basic schematics, etc…  good for any tube audio-maker to keep on hand. I stopped by the shop briefly today and was pleasantly surprised that to see that E.Lyon had found this for me…   Thanks again!  Enjoy…

Mullard_EL37 Mullard_ECC83 Mullard_Circuit

From the why-didn’t-i-think-of-that-first file – Great EZ hack for Octal can transformers

FirefoxScreenSnapz001Via this eBay auction: a UTC A-12 mounted on a plate-retained octal plug, with the pins wired to correspond to the pin-out of an Altec 4722 input transformer.

FirefoxScreenSnapz002It had simply never occurred to me that the mounting-diameter of a UTC A-series corresponded to the mounting-diameter of those octal-mount plates.   Well done sir.  Great idea if you have an Altec 1567, 1566, or ANY piece of old pro audio gear that uses octal transformers – and a great many do.  RCA, Newcomb, Ampex, the list goes on….

Suicide Manual

TAB_666_ExperimentingIn NYC in the mid-seventies, an electronic-based band arose amongst all the guitar punks, a band that was known as much for their confrontational post-beatnik vocals as for the strange and intense sounds that emanated from their famously homemade electronic sound equipment.  A band who has become, in the decades since, one of the few acts that is truly ‘required reading’ in the lexicon of avant-garde rock n pop.  Or, as James Murphy so brilliantly puts it in his apocryphal tale of musical uber-taste, “I was there, in 1974, the first Suicide practices in a loft in New York City… I was working on the organ sounds…with much patience” (skip to 2:50… or, actually, don’t… this song kinda rules).

So yeah I am talking about Suicide.  If you don’t know ’em, check ’em out…  it is amazing+terrifying that this record came out in 1977…  truly truly AOTT.  And plainly awesome too.  I really love this band, and they inspired me greatly in the early 2000s, when I was performing with a punk band in Brooklyn using an analog drum-machine rig based around some old Roland beatboxes, voltage controlled filters, and a CV-generating homemade theremin to control the whole thing.

LISTEN: The_Flesh_Gallows

This felt fairly fresh to me in the year 2001; so that fact that Suicide was doing this same thing 25 years early was mindblowing.  I had to wonder; how the hell did these guys make all the stuff?  Even in the year 2000, DIY’ing synth equipment was fairly unusual for rock musicians; but in 1975?  That was like black magic!  Well I think I found the grimoire.

NEways… kinda a long setup to what will be…  the first OUT OF PRINT BOOK REPORT we’ve had in a while.  And oh boy will there be more coming.  I was recently at a really fascinating estate-sale somewhere in Marin County, California, where I met an elderly engineer who sold me a library of ancient audio-tech books and wished me luck on my travels… the pick of the litter was the above-depicted “Experimenting With Electronic Music,” by Robert Brown and Mark Olsen.  Published in 1974, it is TAB books catalog number 666.  No joke.  This just keeps getting better.

ARP_2500The book starts with some fairly uninteresting discussion of various commercially-available synthesizers circa ’74, but soon gets into a wealth of both schematics and ideas regarding DIY’d audio electronic circuits.  Here’s the TOC:

TAB_666_ContentsThere’s a ton of great stuff in here, and while I honestly have no idea whether or not the particular transistors spec’d in these circuits are still available, I would imagine that there are subs available…  even if you never build anything from the book, I think anyone with an interest in early electronic music will find it fascinating.  Here’s a few projects that I plan to do at some point:

PhotoElectric_Modulator Tremolo_Schem BandSelect_Audio_filter“Experimenting with Electronic music” is available from a few sellers on Abe Books.  It ain’t cheap, but I’ve been digging for these sorta books for 20 years now and this is the first copy I ever came across.

EMI Redd 47 Mic Preamp build

EMI redd 47So I was flipping through Recording The Beatles recently and I was reminded that I had yet to make one of those famous EMI console preamps.  As luck would have it, we were hit with a pretty major blizzard and I had a few days with nothing much to do.  The preamp turned out great, I love the fast (fast for a tube/transformer circuit, that it…), assertive sound of it, and I will definitely be making more of these things.  I’ve been using it primarily for tambourine (with a vintage Senn 409), acoustic slide guitar (with an Altec 660B), mandolin (with my Audio-Technica 813) and acoustic rhythm guitar and shakers (EV RE15).

Here are some of the resources that I used to build the device.  I apologize to whoever originally posted these documents for my lack of attribution; I DL’d them so so long ago that I can’t recall where they came from.


Another Download:  REDD47AmpSchem

And these two images:REDD47_original REDD47

There is a real lack of consistency among these documents, and no I am not going to offer a ‘corrected’ schematic; that being said, if you actually have the where-with-all to fabricate one of these things from scratch I think you will do just fine with the same materials that I started with.  And if you don’t want to do it from scratch: no problem!  Just visit these dudes.  (n.b.: I have never used a drip electronics product personally, so I can’t vouch for them; that being said, they are extremely popular and seem to know what they are doing).

A few build notes

 I used my usual Jensen input transformer (click to DL info) and Edcor output transformer.  The thing sounds great overall, so I recommend these, at least for a first-build of this circuit.  Why spend more?

Very important: this circuit uses a lot of negative feedback. There are also a lot of capacitors in the feedback path.  Each capacitor contributes some hi-pass filtering, which should be below audio range, BUT…  if the capacitor values don’t all ‘play -nice,’ you could end up with so much phase-shift in the sub-audio region that there is 180-degree phase shift in the sub-audio region and you will have a device that ‘motorboats,’  I.E., your ‘negative feedback loop’ is a POSITIVE feedback loop aka a fkkn oscillator.  I had this problem initially.  The device worked fine, seemed to sound good, but at the lowest gain setting (aka the setting with the MOST negative feeback, get it????) I was seeing some 10hz signal pretty prominently in the audio files.  I guessed that this was due to the fact that I used a 47uf cap by the cathode of the input tube,  rather that 100uf that is specified.  I made the correction and viola problem solved.  HERE’S THE SHORT VERSION:  with this much feedback, component values are critical.  BTW, who knew that Apogee A/D convertors work so well at 10hz???

The Redd 46 has a three position gain-switch, and also a ‘gain trim’ control that does very very little.  Think of it as a ‘channel matching control’ rather than a level control.

Because of the lack of gain control, and the fairly high minimum gain setting, the Redd 46 really needs pads to be used in the studio.  Since I did not leave enough panel room to add i/o pads, I have been using it with some external 10 and 20 db ‘XLR barrel’ pads.  Depending on the amount of drive and crunch that I want in the signal, I have been adding the pad either before or after the preamp (or both!) before the signal hits the convertor.  Therefore, the next time I build one of these, I am going to include two two 3-way (0-10-20) switched pads in the device, one before the input trans and the other after the output trans.  I highly reco that you do the same.   I generally use a pad design similar to this one suggested by JLM audio; never had a problem with it.

BalPad_switched copy

EMI redd 47 with power supplyAbove: another shot of my REDD 47; the box on the right is the power supply; basic voltage-doubler (ala the Altec 1566) with tons of filtering and a choke for the B+ and DC filament supply.  Connection is by a 4-pin amphenol.

I have gotten a lot of questions regarding the enclosure used for the audio chassis:  it’s a BUDD enclosure of some type, I can’t recall the exact product name; it was dead-stock from a local distro, last one they had, and I am guessing that it was manufactured in the 70s.  No idea where to get more of them.  If you know, please drop us a line…

Hi-Gain PA Amplifier Circa 1950

HiGainPA_AmpFrom Radio-Electronics, 1950, comes this circuit by one James Rundo.  Download the article by clicking here:

DOWNLOAD: HiGainPA_Amp_1950

SchematicAbove, the circuit.  The front-end is set up for very low-impedance unbalanced mics that mix through a resistor network through a single  (VERY) high ratio input transformer; so that bit is not very useful. What makes this piece of interest is the unusual tone control scheme.  See the article for the details.  Could make for a really unique guitar or studio bass amp.