Categories
Custom Fabrication Technical

The Old ’76

My latest microphone preamp design is completed and sounding very cool… The Old ’76.

The Old ’76 is a novel three-stage design; it’s not based on any past or current production microphone preamp.  That being said, the circuit is nothing revolutionary: an input transformer (in this case a UTC O-1, as I was temporarily out of Jensen 115s) connects to an RCA 76 tube, biased in textbook (or, at least, RCA-Receiving-Tube-Manual-book) fashion; volume pot follows and then on to a 6SL7 tube with the first stage plate directly coupled to the grid of triode 2; the output is a cathode follower with a Solen cap and onto an Edcor output transformer.   The pushbutton switch (with associated pilot lamp) activates 48V phantom power.  Overall gain is approx. 60db and response is flat 50hz – 18khz.  I am betting that the slight high and low end roll off is due to the UTC O-1; the next build will use my customary Jensen input transformer and we should see 25hz-20khz flat response.

76 tubes were often used in ancient console radios with a large tubular shield positioned around them; the reason for this became quiet clear once I had finished my piece; before I added the above-depicted aluminum plate between the 76 and 6SL7, I was getting some unpleasant ringing on very high frequencies.

I had wanted to build a mic pre with some of these very old two-digit designation tubes for some time now.  Hi-Fi fans seem to love the 76 tube, so I figured there was probably something worth investigating.  76 tubes are readily available and pretty inexpensive; it is a bit of a challenge to find the 5-pin bases that they require though.  AES sells only one 5-pin base, and it’s expensive and oversized.  My prototype unit here used an older Amphenol socket that I dug up somewhere.

Some other miscellaneous design notes: B+ rectifier is a 6×5 tube; hammond 15mh choke was used in the B+ chain; DC filaments, as usual; the phantom power supply has a slow ramp-up when activated; the three-pole phantom switch 1)connects the 48v supply to the main power supply; 2)connects the phantom indicator lamp to the 6v supply; and 3) connects the 48v to 6.8k resistors that actually connect to the mic input jack.  I find a three-pole switch necessary in these instances because there is some ‘drain’ time involved when phantom is turned off, even with a bleeder resistor; disconnecting the 48v right before it hits the mic jack provides 100% assurance that you (I) won’t melt that BK5 ribbon (again).

An A/B test of The Old ’76 vs. the usual API 512 will be posted here in the next month or so.

 

Categories
Microphones

The Mics of ’42

Download a four-page catalog scan of the microphones of offer from Allied Radio in 1942:

DOWNLOAD: Mics_Of_1942

Models covered, with photos, text, and some specs, include: Astatic T-3, JT-30TT, GT-3, N-30, and DN mics; Shure 708-A, 750-B, 730A Uniplex, 55c, 55a, and 555 Unidyne, Shure 7A, 705A, and 70H Crystal microphones; Electrovoice 630, 640, and Cardax dynamics, and V-2, V-1 ribbon mics; Amperite PGL Dynamic and RBHK and RBMK ribbon mics; RCA MI-6205 Aerocrystal Microphone; Bruno WS, SS, and HS high-impedance ribbon mics; plus more.

Bruno Microphones Circa 1942

Astatic Crystal Microphones Circa 1942

Electrovoice and Universal Crystal Microphones of 1942.   The most primitive of microphones.  I recently got the chance to use my ancient Lifetime Model Six Carbon mic on a contemporary vocal session.  It actually worked out great.  This is ATLANTIC CITY, my studio project with T.W.  LISTEN: Ten Past Midnight

Electrovoice and Amperite Ribbon Mics c. 1942

Shure Cardiod Mics c. 1942

Categories
Antique Hi-Fi Archive

Mystery Amp Circa 1955: Mystery Solved. Anyone have a schematic?

*UPDATE NOV 2016:  please read thru the comments section!  In all likelihood, this is in fact an original Mirko Paneyko piece, which means I am a huge A-hole for selling this thing for $180 on eBay in 2012. I only learned about MP in 2016 via a huge collection of old journals I purchased.  He was a titan in the audio field, and certainly one of the most interesting historical figures in the Bridgeport area in the mid 20th century.  Read his NYT obit here. – ED

  I picked up a big pile of old audio equipment this past weekend; notable items included a Shure Level Loc, a massive Bogen tube pa head, a kit-built Acrosound ultralinear 5881 amp, and a Gibson acoustic gtr case from the early ’60s (no gtr).  Also included was the mono amplifier shown above.  It’s a push-pull amp, cathode biased 807s, with 6SN7 driver and phase inverter; there is also a 2x 12A_7 preamp section with this ‘remote’ control section attached via 10′ of cabling…

After a little cleaning, the amp actually works fine if I remove the ‘remote’ and input directly into the final 12AX7 stage prior to the phase inverter.  As far as actually using the remote, well, I can’t quite figure out what sort of patching needs to be inserted with the two RCA jacks and one RCA male plug coming out of the face of this thing.  It’s a little bewildering.  If anyone can tell me who made this amplifier, I imagine I could find the schematics somewhere.  There are no markings on the unit anywhere besides an inked serial number inside the chassis and the letters ‘MP’ on the remote.  I am sure that this is a factory-wired unit, as there is tamper-paint on every solder joint.  BTW, I added the on-off-switch and the IEC socket on the side, so don’t let those two details derail your ID’ing efforts.  I am guessing that this a circa 1955 unit as the 12AX7 was only introduced in 1953, and the 807 craze was in the process of winding down by ’55…  so we’re likely looking at a unit made between 1953 and 1958.  Any ideas, please let me know.  This thing is 95% of the way to full operation and I’d like to get it running strong again.  It’s a tremendous looking piece, and it has a lot of volume.

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Updated: the mystery has been solved.  This amplifier was built by the Saulnier Music Service of Columbus, Ohio; so sez the son of the man responsible.   Read the comments section for the full story.  I am still in a need of a schematic (or even just a manual?) for this thing so that I can figure out what do do with the assorted preamp jacks n’plugs.  According to our poster, this circuit came from a transformer manual; which would likely mean a Stancor audio-manual circa 1954.  Anyone?

Categories
Uncategorized

(Updated: Link To) Live Radio Show: The Ladies of Psychedelic Folk: 11/14/11: 89.5 WPKN:

Monday November 14 2011: Tune in tonight to WPKN 89.5 on yr FM dial in Southern Connecticut/Northern Long Island: or listen live in high-quality at www.wpkn.org.  I will be appearing as a guest on Steve di Costanzo’s excellent program ‘Radio Base Camp’ presenting a show I’ve put together on the Ladies of Psych-Folk.   We’ll be listening to some classic and lesser-known gems from the late 60s, as well as more recent artists who have drawn inspiration from that era.  Steve had me on air back in June; you can check out that show here. Hope you enjoy the show.

UPDATE: Steve has added the show to the WPKN archives.  You can stream it until (insert personal favorite apocalyptic event) at this link.

Categories
Uncategorized

Open Studio Event 2011

This coming weekend: November 12+13 2011: we will be having another Open Studio event at our arts building in historic Bridgeport CT.  Forty artists and fine craftmakers will open their studios and exhibit their work and their work-practices in our century-old lace factory, and this is only one part of a larger Bridgeport Arts Trail going on that weekend (read some media coverage of the event here).   Believe-it-or-not, our dusty lil post-industrial town features not one but three very large art-space buildings, and there is some fantastic work to see (and hear…).  After you’ve come by to listen to some of my Recycled Champs, the Model 22277 hi-fi amplifier, and my latest development in all-tube mic preamps (w/ ancient RCA 76 tubes), be sure to check out the work (and amazing studio) of the photographer Tom Mezzanotte, world-renowned quilter and textile artist Denyse Schmidt, and all the odd characters that have assembled in this strange+semi abandoned place that we call BPT.  If you’re lucky, you might even get to commission some print-on-demand work from my wonderful wife E., who will have numerous print-publications of her work for sale.  Details and directions below.

Categories
Custom Fabrication Uncategorized

A couple of recent guitar amplifier builds *Revised (2)*

Cassius #10; aka #10 in the the ongoing series of Fender Champ-derived guitar amps built into recycled ‘found’ vintage speaker enclosures.  See here and here for some of the earlier examples. #10 is already sold, but will be avail for examination at the upcoming Open Studios event at our building this coming weekend.  Cassius #10 is my first ‘Cassius’ with an EL84 output tube: it’s basically the front end of a tweed fender champ married to the power stage of a Vox AC4.  Add a nice full-range 8″ Alnico HiFi driver and holy shit does this thing sound great.  Solid-state rectifier, no choke, extra filtering stage in the power supply.  Output transformer is from a 1950s R GE HiFi console; all other parts are new.

Of all the pieces that I have posted on this website this the past year, the one that gets the most page-views is still my scan of the 1970 ORANGE amplifiers catalog.  I’m much more of a large-combo-amp guy then a stack-guy so i’ve never owned an actual vintage Orange amp head.  That couldn’t stop me from building one though.

Above, my version of an Orange Graphic 80.  Two EL34 output tubes, two 12AX7 preamp tubes, effects loop, variable low-cut filter, adjustable ‘fixed’ bias.  Unlike an actual Orange Graphic 80, I used a high-voltage mains transformer and a 5U4 tube rectifier (Orange originally used a voltage doubler and a diode bridge).  I also used a slightly different supply for the grid bias voltage as my Hammond power transformer did not have a bias winding.  For the output and choke transformers I used pulls from a beat 1950s RCA PA head; it was rated at 30 watts (7027 tubes) so we’ll see how long this output transformer lasts….

The most unique feature of the Orange amps is the bit labeled ‘filter’ here; Orange called it the ‘F.A.C’ control; it’s simply a 6-position high-pass filter that follows the coupling cap before the phase inverter.  It’s composed of a 6-position rotary switch with 5 carefully-chosen caps strung in series between the taps.   Simple as it is, it does make for a much more versatile amplifier.  I recently built this circuit into one of my Cassius amps (already sold) it worked great there too.

Above, the preamp wiring. 

Want to know more about building your own Orange Graphic from scratch? Follow the link below to READ ON…

Continue reading “A couple of recent guitar amplifier builds *Revised (2)*”

Categories
Altec Microphones

Studio test of obscure circa 1965 Altec dynamic microphones

L to R: Shure SM57; Altec 684 Omni; Altec 682 Cardiod; Altec 683 Cardiod

Altec made a great number of different microphone models in the 1950s and 1960s.  A certain few of these are still widely used in recording studios today: most notably the 639 ‘Birdcage’ dual-element microphone (see here and here) and their various small diaphragm ‘Laboratory’ condensers (see here, here, and here).

During this period Altec also made a variety of conventional-looking dynamic microphones, some of which have quite good specs on paper.  Today we’ll be having a listen to the Altec 682, 683, and 684.

I’ve prepared three stereo audio tracks which all document an identical solo guitar performance which we tracked in the big room at Gold Coast Recorders.   In each of the three tracks, you will hear a new-ish Shure SM57 in the left speaker, and the selected Altec mic in the right speaker.  I chose an SM57 as a reference because it is a microphone that most of us are very familiar with and it is often used to mic electric guitar amps.  I placed the mics a big further back than I would generally use a dynamic-mic on a guitar amp in order to minimize any differences that might result from the slight variation in mic placement in relation to the amplifier.  All signals were taken from the microphone into identical Sytek mic preamps and then directly into Aurora Lynx convertors and into Protools.  No processing whatsoever was used other than minimal Digidesign MAXIM on the bounce-buss to ensure strong playback level; it was taking off 0.3db at most.

Levels were matched initially by running a 1K tone into the guitar amplifier and then fine-tuned on playback to within the tightest possible margin.  The 684 Omni required 30% more gain to reach an equal level; the other three mics were within 5% or so of each other in terms of output.

Alright now that you’ve seen the setup, here is the audio:

SM57 vs Altec 682: SM57L_682R

SM57 vs Altec 683: SM57L_683R

SM57 vs Altec 684: SM57L_684R

Have a listen and draw your own conclusions.  My quick assessment: the 682 sounds pretty similar to the 57, but IMO a lot prettier, a lot more detailed, and just more presentable in general.  The 683 sounds thinner than the 57; bass is notably lacking and there is an aggressive character to the mids.   Not sure that I would ever select this mic for anything.  The 684 sounds like… an omni mic, so it’s not a valid comparison to a 57, but it does sound pretty decent as an omni.  Might make a good under-snare microphone.

All of these forgotten Altecs are available cheaply on eBay from time to time.  I’ve never come across one at a flea market or swap meet, though, so I don’t think they are very common.  From what I can tell from my limited sample-pool, the ‘A’ designation after the model-number indicates that the mic uses an XLR5 (rather than the current standard XLR3) connector.  If you get one of these ‘A’ designated mics, you will need to find an XLR 5 female jack.  Wire an adapter to XLR 3 as follows: (XLR5:XLR3) 1:1, 2:3, 4:2.   The ‘B’ designated mics seem to have our current-standard XLR3 jacks.  Again, I am not 100% about this distinction, so check closely before buying if you don’t wanna be soldering adapters.

Categories
Microphones

University Microphones circa 1963

Download the eleven-page University modular-microphones catalog circa 1963:

DOWNLOAD: University_Microphones_1963

Models covered, with text, specs, and photos, include University model 401, 402s, 501, 502s, 403L, 404L, Model 70, and Model 71 dynamic mics; and the associated Model SA10, PA10, SSP10, SP10, and CC10 microphone bases. By ‘Bases’ I refer to the lower-half of the microphone itself: the connector, stand-mount, and switch assembly.  Apparently the user could ‘mix-and match’ among the various University capsule/transformer mic bodies and whatever jack/mount/switch assembly the user preferred.  The catalog itself is formatted with a 1/3rd-page insert in order to facilitate comprehension of this ‘feature.’  Here’s an example:

I purchased a well-worn University handheld cardiod dynamic mic recently; it was a model 8100 I believe.  It was the first University microphone I can recall finding.   I picked it up with a nice older desktop stand and a big pile of useless old cabling for a few bucks.  It worked well, and once I constructed a proper cable for it was moved along.    University was a subsidiary of Ling electronics, as was Altec; that being said, there was no way to identify the 8100 as being possibly Altec in origin other than the fact that it used an uncommon XLR4 cable connector, as most 1960s Altec mics also do.  I don’t know if there is any significance to this.  The 8100 was sold to me with possibly the best microphone provenance I have heard in a long time; the junk dealer told me that it had been the announcer mic at the Wallingford Speedway, a (now defunct? Leveled?) Connecticut auto racetrack that I remember vaguely from my early childhood.

A similar model 8100 recently sold on eBay for the terrific  sum of $0.99; new in box, nonetheless; no stories of former racetrack glory accompanied that particular mic.  Dig the fantastic graphic design on the box.  Original eBay listing on-view here.

 

Categories
Antique Hi-Fi Archive

University Speakers Circa 1963

Download the complete 20pp 1963 University Speaker Systems catalog (in two parts due to file size)

DOWNLOAD PART 1: University_1963_p1

DOWNLOAD PART 2: University_1963_p2

Products covered, with text, specs, and photos, include: University Medallion XII speaker system; Classic Mark II and Classic Dual-12 speaker systems; Companion II, S-80, Companionette, and Mini-Flex, and Mini bookshelf speaker systems; the full range of two-and-three-way coaxial University components including 315, 312, 6201, 200, 308, 200, UC-153, UC-152, UC-123, UC-122, UC0121, and UC-82; and University woofers, midranges, , tweeters, and crossover networks including C-15HC, C-12HC, C-8HC, C-15W, C-8W, HF-206, UXT-5, 4401, C-8M, Sphericon, H-600, Cobreflex, T-30, T-50, N-1 High Pass Filter, N-3 acoustic baton, N-2A and N-2B crossovers, plus more.

Above, the flagship Medallion XII system in a variety of “select-a-style” grilles.  There is a pair of Medallion XII (in French Provincial trim, naturally) on eBay right now for $200.  University Sound was founded in 1936, and became part of the LTV_Ling_Altec family of brands sometime before 1963, and eventually became absorbed into the Telex corporation.

Above, the University Classic Dual-12 system.  These things look serious.  I currently own a University single-12 system; it is a corner unit from the Mono era; its has very nice cabinetwork and it sounds surprisingly good for a full-range 12″ system.

This catalog is obsessively dedicated to selling speakers to a male/female couple.   Nearly every human image consists of a sample couple in the throes of consideration.  Which system to buy for our home?  So much to learn.  Let University help you.  Honestly I can’t read the emotions in these faces.  Perhaps early-1960’s people had a different feeling-set than we experience in the (post-Vietnam/LSD/Civil Rights) era.  Confused by these photos, anyhow.  This series seems to suggest: 1) ‘quiz-show-don’t-know-the-answer’; 2) ‘I’m not really paying attention to you’; 3) (undeserved?) smugness; 4) ‘we’re on a boat, and you’ve been naughty.’

Categories
Publications Technical

Stancor Amplifiers and Full Transformer Data c.1937

The Stancor ‘306’ 6-watt PP audio amplifier

Download the 1937 (‘third edition’) of Stancor Transformers’ ‘Amplimanual,’ a 24pp publication which conveniently combines schematics for ten original audio amplifiers with full data for their entire line of transformers.  If you (like me) have some pre-war Stancors lying around and you are unsure what exactly what the specs are, this is a godsend (blogsend?  awful).

Split into two parts due to size:

DOWNLOAD SCHEMATICS:Stancor_Amplimanual_Schematics_1937

DOWNLOAD 1937 STANCOR  DATA: Stancor_1937_Transformer_Specs

Schematics are provided for Stancor’s own 303, 305, 306, 312, 318, 320, 325, 335, and 360 audio amplifiers.  The first ‘3’ in the designation seems to represent this ‘third’ edition of the publication, and the second two digits correspond with the stated audio-output of the particular device.   Looking through the schematics, you will see the following tube types most often:  6F5, 6C5, 6J7, 80, 6V6, 76, 6N7, 6L6, 6A6, and 6A3.

Above, the schematic and parts list for the ‘303,’ a microphone pre-amp.  I will be building one of these shortly.  I was most excited by this publication due to the 76 tubes in a few of the circuits.  I am close to completion on a novel microphone preamp design that uses a 76 tube as the input stage and I am in-general trying to get more into the early ‘two-digit-designation’ tubes: the 75, the 76, the 42, 80, etc…   we are looking back etc etc.

Above, an image of the Stancor factory which describes a certain transformer-manufacturing process which I will not put into text because I get enough porn spam as it is. 

Several completed Stancor amplifier units

Above, several transformer units photographed for the catalog with their model-numbers included via practical photography.  What a great design move this is.  I bet we see a return to this product-photography technique in the coming years.  ‘If you can find a way to do-it practically (rather than digitally), then do it practically!’