Author: chris

Categories
Altec Pro Audio Archive

Altec Professional Audio Controls Paper Circa 1960’s

Around the time that ALTEC introduced their 947X series of solid-state plug-in amplifiers, ALTEC staff engineers Arthur Davis and Don Davis published the following paper in AUDIO magazine (see my previous post on AUDIO mag).  ALTEC then reproduced and re-printed the paper as promotional material. I have scanned and uploaded the fill 12-page document.

DOWNLOAD: Altec_Professional_Audio_Controls

Covered in this document: the 9200 modular console, the 9704A transmission measurement set, and the various ALTEC passive equalizer units of the period: graphic, shelving, and pass filters.

Check out the publication.  It is a good quick primer on early impedance-matched mixing systems.  In the future, I will post more extensive documentation on these ALTEC consoles and filters.

Categories
Recordings

The Sound of the Front

A friend recently asked me if I could digitize a record for him.

T’s  mother passed not long ago, and in her possessions he found a small record-album that a suitor had recorded for her while serving in WWII.

It seems that Pepsi-Co provided these machines for the use of GI’s.  There is small print on the disc itself that reads ‘Recordisc,’ which was a popular pro-sumer disc recording unit of the era.  I have not been able to determine exactly what the recording apparatus for these Pepsi-branded discs were, but I imagine it was not dissimilar to these:

(web source)

When T first asked me to do this transfer for him, he was very concerned with the recording deteriorating due to the playback.  For this reason, I captured the material on the first-pass.

I used my shitty little VESTAX ‘porta-trax’ or whatever player, as it is my only deck that does 78 RPM. Why did I assume 78 RPM?  Well, the 33.3 LP or the 45rpm 7″ were not in common use during WWII,  so 78b RPM was a safe guess.

The recording was actually quite good, aside from the surface noise.  Since the VESTAX applies an RIAA equalization curve (which was NOT used in 194X), I had to re-EQ the audio in Pro Tools.  I attempted to research the Recordisc machines in order to determine which pre-RIAA pre-emphasis EQ curve they used, but I could not find any information on this.  So I use my best judgment.  I used my ears.  I applied a 24db/oct lo-cut at about 200hz, a 12db/oct hi-cut at around 5k hz, and then boosted a bit at around 2200 to help the intelligibility.  Two stages of compression were then applied.

Here’s the result.

LISTEN: AudioLetter_WWII_serviceman_to_ladyfriend

This is powerful for a few reasons.  Generally, when we hear voices like this, it is in the context of a film or radio news program of the period.  Although this GI is reading from a piece of paper (it sounds like), he is not an actor, and he is not acting; this is intended for an audience of one.

In case you were wondering: the woman in the photographs is in fact the addressee of this recorded message.  This man did come home after the war. He did not marry the woman that he is addressing, although they did remain in touch; and he is not T’s father.

Categories
Guitar Equipment Pro Audio Archive Publications

Fender Album Of Stars Promotional Magazine c. 1968

Download the entire 32-page Fender ‘album of stars’ promotional magazine, circa 1968:

DOWNLOAD PART 1: FenderAlbumofStars1

DOWNLOAD PART 2: FenderAlbumOfStars2

Apologies for the weird alias-ing.  I’ll get better at scanning eventually.

A special PreservationSound nod to Merry-Go-Round frontman Emitt Rhodes (standing), aka the father of home recording.  IF you are not familiar with Rhodes and his outstanding work, check him out…Also be sure to scope this amazing early music video for one of his best tracks. “Hey how do we let people know that he plays EVERYTHING on these recordings?”

Some of the images in this 32-page ‘album’ have been reproduced often; for instance, the highly-dubious Dylan-with-Jazz Bass.  Many, though, have never been seen by those who do not possess the actual document. This is a fairly rare item these days, as it was created with the intention of being cut-up and pinned to one’s wall.  There are actually cut-lines printed in the margin of each page.  So dig in….

Artists include:  Union Gap, Mike Bloomfield and the Electric Flag, Brenda Lee and the Casuals, The Fifth Dimension, Sebastiao Neto with Sergio Mendes and Brasil 66, Oscar Mesa and Mike Saluzzi with Roger Williams, The Merry-Go-Round, Vic Gaskin with Cannonball Adderley, Oscar Brown Jr., Herman’s Hermits, Chad and Jeremy, Bob Dylan, Wayne Newton, Sonny and Cher, Herb Alpert and the Tijuana Brass, Lee Michaels, Noel Harrison, Edgar Willis and Barry Rillera with Ray Charles, Ian and Sylvia, The James Cotton Blues Band, Duke Ellington and Mercer Ellington, The Beach Boys, Don Ellis (check the prototype echo ((?)) unit), The Baja Marimba Band, The Paul Butterfield Blues Band, The First Edition (feat. Kenny Rogers on a Coronado Bass II), Rick Nelson and James Nelson, The Chambers Brothers, The Byrds, and a dude who apparently played a Stratocaster guitar named Jimi Hendrix.

Categories
Guitar Equipment Pro Audio Archive

Yamaha Guitars And Guitar Amplifiers 1968

Download the entire 12-page 1968 Yamaha Guitar/Amp Catalog (USA region):

DOWNLOAD: Yamaha_guitars_amps_1968_catalog

Models covered in this publication: Model 150, 120, 100, 80, and 60 Classical guitars.  Model FG-110, FG-150, FG-180, FG-230 steel-string acoustic guitars.  Model SA-50, SA-30, SA-70, SA-20, and AE-11 electric hollowbody guitars; and the TA-60 and TA-30 guitar amplifiers.

I have owned and used several of these instruments.  The electrics are really very cool, but keep in mind that most examples will need a neck reset and/or plane in order to play like a new guitar.  Dig that dark green finish on the bass though.  Killer.

It has often been noted that Jimmy Page toured with Yamaha acoustics in the early 70’s, which may be why Japanese Made ‘red-label’ Yamaha acoustics are currently in-demand.

Yamaha has used the term ‘natural sound’ for many decades to market a wide range of different audio gimmicks.  The only constant seems to be that ‘natural sound’ represents Yamaha’s willingness to try odd new things in a constant technological struggle to achieve more accurate sound-reproduction.  This early iteration of ‘natural sound’ seems to consist of these odd trapezoidal ‘happy-meal’ foam speakers.  We had one of these amps in our band back in the 90’s and it was heavy as a bastard and very dull-sounding.

Not sure if this was Yamaha’s own technology or if they licensed it from another firm.  In any event, these odd speakers made their way into an obscure Fender combo amp in 1969, the Bantam Bass.

(web source)

The Bantam Bass is essentially a Bassman 10 with one large foam speaker in place of four 10″ drivers.  It was a short-lived product.

Categories
Pro Audio Archive Publications

Sears Silvertone Sound Systems 1940

Download a 17-page scan of the 1940 Sears Silvertone sound system catalog:

CLICK TO DOWNLOAD (10mb) : SearsSoundSystems1940

The PA, or Public-Address System, was still relatively new technology in 1940.

It’s hard for us to imagine any of the above scenarios without some sort of microphone/amplifier/speaker apparatus in play.  The human voice was not designed to clearly address dozens or hundreds of people who may or may not be paying attention.  Sure, we can yell pretty well; but the careful inflections of speech require an intimacy that cannot be accomplished on a mass scale.  Without some ‘reinforcement.’  Enter the Vacuum Tube.

I have owned quite a few of these antique units.  A few notable units have been restored; many more were gutted for parts, their chassis delivered to other uses.  One tip: beware the input transformers on these early PA units.  they are rarely magnetically shielded.  The physical orientation of the input transformer unit relative to the power transformer is crucial.   You can determine optimum positioning by placing your power transformer in the intended position.  Send 120V AC to the primary of the power transformer.   Then connect a low-impedance headphone (EG., a SONY 7506) to the primary or the secondary  of the input transformer (try both).  Now move the input transformer around relative to the power transformer.  If the transformer is unshielded, you will clearly hear an optimum (less hum audible) position.  This trick also works great for determining optimum output transformer position for hi-fi amps and guitar amps btw.

Categories
Pro Audio Archive Synthesizers

Polyfusion Modular Synthesizers

Polyfusion is an electronics firm in the Buffalo, NY area which began in the mid-1970s.  According to their very outdated website, their sole standard product these days is a frequency-shifting device intended as a feedback-reducer in (presumably voice-only) PA systems.   I do not know anything about these devices beyond what I have seen online, but I did recently come across a large folio of promo materials from the 1970s.  It seems that Polyfusion got their start making modular synths which were used by such folks as “Vince Clarke, Ken Hemsley, Scott Humphrey, Masterworks, Steve Porcaro and Tangerine Dream.”

Anyhow.  Here is the 1977 Polyfusion catalog and pricelist.  Enjoy.  If anyone is interested: I also have another 24 pages of detailed specs on each one of the modules, so drop me a line if you want to see those too.

DOWNLOAD THE 6-PAGE SERIES 2000 CATALOG: Polyfusion_1977_catalog


Categories
Microphones Pro Audio Archive

RCA microphones catalog circa 1965

Click the link below to download the entire circa 1965 RCA microphone catalog.

DOWNLOAD: RCA_Circa1965_Catalog

A lot of interesting pieces here.  I personally love the BK5.

The BK5 is an unusually bright and aggresssive ribbon mic.  Highly recommended for…  pretty much any spot-mic task.  Hands-down better than the Royer R121.  And about 1/2 the price.  Not so reliable tho…  mine has broken twice in as many years.  but good god what a sound.  and the pattern is super-tight.

Categories
Uncategorized

Where do you find all those old tubes?

When folks learn that I build and service vacuum-tube based audio equipment, some of the first questions they ask are: Is it hard to find those old tubes?  Where do you find them?  As it turns out, lots of different places.

The RelaxAcizor was, depending on who you ask, either a quack-medical/exercise device or a sex toy that was marketed clandestinely to women in the 1950s.  It consists of a voltage amplifier in a chassis with a series of electrodes that attach to the (female) body on numerous pads.

Looks fairly horrifying.  Anyhow, using dials on the amplifier-unit, the user can vary the amount of voltage that the various muscles experience.  The result?  The manufacturer claimed that it would lead to ‘effortless weight loss.’  But as Peggy Olson experienced in episode 1.11 of MADMEN, it is more likely to lead to orgasm.

(Peggy Olson, noted audiophile.  WEB SOURCE)

Anyways… I bought a partially-disassembled RelaxAcizor for a few dollars at the flea market yesterday.  It was oddly missing its case, so the rear of the chassis was exposed.  This is a crucial point.  Because the innards of the unit were visible, I was able to see that it contained a VT-52 tube.

The VT-52 is a very valuable and useful audio tube.  It’s basically (BASICALLY..) a 2A3 designed for 6.3v through 7v filament voltage rather than 2.5 volts.    This tube has a huge cult following.  Check out this deep website dedicated solely to the VT52. I love the sound of the 2A3.  My main home-music listening amplifier for the past 5 years is a stereo 6SL7/2A3 amp that I built based on a schematic from Angela dot com.  There are a ton of great, simple schematics for Single-Ended high-fi amps that use the VT52 as the output tube; and unlike the 2A3, which requires an unusual filament voltage and requires an unusually low output transformer primary, it appears that the Vt52 will work fine with normal ‘guitar-amp’ type 5K Output transformer.  Directly-heated Fender Champ?  Yes I think so.  I am inclined to recommend this schematic over the others.  The 2A3 likes to be fed by a low-impedance signal and I would bet that the VT52 is similar in this regard.

Carving up the RelaxAcizor also resulted in this nice wrinkle-finish chassis, which will find a good home someday in a a future project.  E commented that perhaps I cut up the unit because I felt threatened by it.  Well, either that, or the fact that VT52 tubes go for upwards of $100 on eBay.  $300 if they are W.E. branded.

Alright so what’s the point?  Search web forums and you will be told that the VT-52 is a very rare, mysterious tube.  OK.  But consider that over 400,000 RelaxAcizors were sold in the US.  That’s a lot of expensive directly-heated triodes sitting, hidden, in junk piles throughout this country.  So get digging folks.

One warning:  you might have a hard time prying the R/Z from the hands of this lady.

Categories
Uncategorized

Scully 280 tape machines. Not Preserved.

Scully was one of the main US makers of professional multi-track tape machines through the 1970s.  Scully was based in our fair city of Bridgeport CT.  Wikipedia has no information on this classic manufacturer; in fact, they incorrectly identify it being from ‘bridgewater connecticut.’  I’ve been slowly accumulating archival material on this company and hope to have a comprehensive treatment together at some point.

Earlier this week I bought a full truck load of old Scully and Ampex tape machines for a few bucks (no joke).  I think that there were about four Scully 280 2-track machines, several Ampex 351s and PR10s, a 16-track scully 2″ machine, and a few other odds and ends.  My truck is currently out-of-commission awaiting some parts, so I was limited to taking just the stuff that would fit in my VW.  This meant leaving the transports behind and just taking the electronics portions of a few of the machines.

The most exciting piece is this Ampex 3761.  It needs a complete restoration (nearly every part and connector is rotten), but the chassis/faceplate and UTC transformers are intact, so I think I will give it another life.  The 3761 is not a particularly useful device, but it does have an incredible pedigree.   It is a four-into-one microphone level mixer which uses the excellent 5879 pentode tube, and some of the best input transformers that UTC (or anyone else) ever made.  The 3761 was used in order to mix four microphones onto one track of an Ampex tape machine (in fact, it gets its power from the tape machine).  And what recordings were made using these devices?  How about most of the classic STAX recordings.  Good God.

Anyhow, seems like this thing deserves another chance.

How about the rest of that stuff though?  It all dates to around 1965-1970.  None of it seems to have been maintained since 1990, and everything was generally filled with dog hair, dead bugs, and bits of food that (presumably) mice secreted away in there.  Yes it was really that nasty. So i was not about to risk a major biohazzard restoring this stuff.  The only other option:  Chop it up.

Each of the 280 chassis contain a number of excellent hermetically-sealed transformers: a UTC A18, UTC A39, and a very large Freed 600:600 (split) transformer. I have yet to find a UTC A-series transformer that did not work, so I am reasonably optimistic.

Three of the 280s also had a UTC 0-1 500:50K input transformer.  Many of the 280s also had clean XLR jacks, lamp holders, and API VU meters.  So it was a good harvest in general.

I do feel a little guilty about chopping up these classic units, made with care here in BPT; but I have a plan to earn back the audio karma.  Once I can track down the schematic for the 280, I will clone the mic pre-amp circuit, and build a few stand-alone 280 clone pre-amps using the original transformers, meters, and whatever other cosmetic parts that I salvaged.  I have been waiting for the right solid-state pro-audio project to present itself, and I think it found me.

It was a little painful to dumpster the carcasses; I felt a little better after K told me that someone shortly thereafter pulled them from the dumpster, shouting excitedly that they were brass, and therefore valuable for salvage.  One person’s junk…

Categories
Guitar Equipment Technical

Premier 88: ready to go.

After probably 14 hours of work and $200 of parts, my Premier 88 is working 100%.

As I described in an earlier post, the Premier 88 is a rare and highly unusual instrument amplifier from the 1950s.  It consists of an amplifier unit and a speaker unit; but rather than the amplifier unit sitting atop the speaker, like most every other 2-piece amp, the 88’s amplifier sits beside the speaker cabinet.  The two sections clasp together with luggage latches.  It moves as one (very large and heavy) piece.

This odd side-by-side form-factor is not the only unique feature of the 88.  Check out the control panel.  Rather than conventional bass/middle/treble knobs, the ‘instrument’ channel of the 88 has 5 organ-stop-type levers that can be switched in or out.  Each lever is a bandpass filter.  IE., if you depress all 5 levers, you get the full tonal spectrum.  If you depress none of the levers, you get silence.   The ‘Microphone’ channel also has a pair of unusual tone control switches; they seem to be hi-cut filters.

Here are some examples of the sounds that the 88 produces.  Right channel is an SM-57 close to the speaker; Left channel is a 414 in omni approx 10 feet away.

LISTEN:  Low_and_High

Listen: Mid_only

The trem is super weird and extreme. Here are a couple of examples:

Listen: Trem_low_settings

Listen: Trem_HighSpeed

***********

*******

*****

**

In all honesty, this amp was a pain in the ass to service.  When I first brought it into the shop, it did turn on and pass signal; the tremolo sort-of worked, as did all of the tone controls.  It just sounded terrible and it had no output.  The longer it ran, though, more and more parts seemed to fail, starting with B+ resistors and then moving on to the 50 year-old tubes.  So eventually I ended up replacing most of the components in the amplifier.

When I first opened it up, I saw tha someone had added a Pilotuner mono FM receiver to the speaker cabinet.  I removed the tuner, and I then had to fabricate cover-plates for where the tuner face and tuner knobs had been.  I used aluminum plate stock.  That was the first piece of work.  And then:

*replaced the 15″ Jensen Alnico speaker with a new Jensen 15″ ceramic (there was a weird rattle in original speaker)

*replaced all electrolytic capacitors in amp (approx. 20)

*replaced all B+ and plate-mixing resistors in upper preamp chassis (approx 15)

*replaced all caps in tremolo circuit (some needed to be replaced twice in order to get the right response)

*clean all tube sockets and replace 3x 12ax7 in pre-amp.

*add grounded AC line to power amp chassis

*replaced 6L6 and 5U4 and 12au7 tubes in power amp chassis

Good lord.  Was it worth is?  Who knows.  Once you start a restoration like this, you kinda just need to push on through until it’s done done done.  This is possibly the only working example of this amp in the world, so I felt like it deserved a chance.

The repair was difficult owing to 2 conditions:

*There is no schematic available for this particular iteration of the Premier 88, and the pre-amp is extremely complex owing to the bandpass filter arrangement.

*The amplifier is split into 2 sections: The top half is the pre-amp and trem circuit, and the bottom half is the phase inverter, power amp, and power supply.  These two sections are joined by two cables: a shielded RCA line (audio signal) as well as an octal snake that carries B+, ground, heater lines, and tremolo defeat control.  Owing to the extremely short length of these two cables and the manner in which they pass through the tight trapezoidal enclosure,  the preamp cannot be operated unless the unit is fully assembled.  So… the preamp circuit cannot be operated while its circuit is accessible.

Now that all is said and done, it is clear that I would have benefited from making an octal extender cable so that the preamp circuit could be accessible while active.  Hindsight is of course 20/20.

A few things other repair tips that this repair has illustrated:

*If you are missing a schematic:  don’t assume that the plate resistors for 12A_7s are 100k ohm.  The 88 had 270k ohm plate resistors.  Generally speaking, when i get an old, noisy amp, I just replace all the 100k resistors, assuming that these are the plate resistors.  Bad carbon-comp plate resistors are often the source of weird intermittent noise in guitar amps.  But not in this case!  Premier used 270k ohm.

*Alnico speakers definitely sound better than ceramics for old guitar amps.  I always suspected this, and now I am convinced.  Wish I had sprung for the extra $100 for the Alnico Jensen.

*Don’t assume that working tubes can’t be causing weird intermittent problems.  I am generally pretty trusting of working preamp and rectifier tubes, and  I am often quick to assume that B+ resistors are bad, when i fact, it COULD also be the tube…