WE/Altec 755 Part 2 (2 cf box)

As many of you know I am an open baffle advocate and have used the 755A and 755C in this concuction for years. However, I recently attended a radio show event after a few years of hiatus and saw my friend Chong Ong. He handed me these ~ 2 cubic foot "homebrew" sealed boxes designed for use with the 8" WE/Altec 755 speakers. According to him these cabinets were acquired from a retired WE engineer which encouraged me to give the sealed box enclosure another chance.

In the past I have experimented with two types of slanted 2 cu. ft. enclosures - an original Altec 618 and custom built 622 using 1/2" plywood - and always ended up with mixed results. The above cabinets look like the 618 and the dimensions are - 22"H x 17"W x 10 1/2" top depth x 13 1/2" bottom depth - using 5/8" plywood instead of the 1/2" used in the original Altec 618 Utility cabinet. The panels are lined with ancient type of damping material known as "Kimsul", which reminds me of crepe paper. I have seen this material inside Western Electric 753 and 757 loudspeaker systems and even as wrapping material in old tube boxes.

Altec 618

Custom Altec 622 with Altec 408A

The first driver I tried was the 755C but these observations were also validated when I installed the 755A and 755E. Compared to the open baffle, this cabinet gives an impression of quicker transients and dynamic nuances which Joe Roberts call "snap" which I could never achieve from dabbling with the 618 and 622. My main frustration when I experimented with the aforementioned cabinets was, both sounded slow in spite of the many tricks I tried - walls lightly damped with pillow stuffing [Dacron], bare "lacquered and resonant" panels and etc.

Anyway, along with the "snap" comes a more forward soundstage presentation. There is a bit of a midbass hump in the 90-120 hz region reminiscent of an LS 3/5A, most evident with the 755C and 755E because they extend lower in the bass. Bass aficionados will probably prefer this cabinet over an open baffle because of this sonic illusion. But remember that even with open baffles, there is not much solid bass below 60 hz on any of these drivers. For that matter I never heard a modern high-end speaker with an 8" woofer that can go down flat to 50 hz and still possess a lucid midrange like these vintage units. The midbass bloom is less obvious with the 755A and overall this was the best sound I got from this box.

Even if the pancakes are claimed to go up to 15khz, they sound like the highs begin to drop slowly around 9khz whereas the 755A still has some energy past its 13khz limit. This may be a psychoacoustic phenomenon given that the pancakes have been redesigned to extend almost an octave lower and lost the "exotic" cone chemistry of the 755A which brings out the even more glorious midrange and silky highs. As many of you already know specs really do not mean much in real world conditions.

The lack of high frequency extension in the "pancakes" is more apparent in the 2 cu. ft. box and I was compelled to use a super tweeter. The Altec 3000 is a natural choice but since this is hard to find and pricey I found the Fostex FT-17H as an excellent and modestly priced [$70/pr.] alternative. I use a 1uf oil filled capacitor and an 8 ohm attenuator to hook up either tweeters to fill-in the drooping response above 10 khz on these drivers. With the 755A, I did not deem it necessary to use a super tweeter. Even the "ribbon-like" Altec 3000 can diminish the purity of the high frequency abilities of the 755A if not attenuated and crossed over properly. If you insist on extending the 755A's, I can only recommend using the 3000 with a .5uf oil cap and attenuated judiciously.

When I designed the JEL SE300Bdx, my only reference speakers were the 755As and 755Cs in open baffles. The 755As can tend to sound peaky if driven by a brighter sounding amplifier or source component while the 755C and 755E are more forgiving. In terms of "apparent" sensitivity/efficiency, the 755C has a slight edge over the "A" and "E". I need SE300B power to enjoy large scale symphonic music with the 755A and 755E. With the 755C I can get by with an SE2A3 amp. However this does not prevent me from using microwatt SE71A for listening to small scale music on any of these drivers.

Like I said in my SP17 homebrewer article, the 755/OB combination reminds me of the Quad ESL57 with greater dynamic range and sensitivity. This 2 cubic foot box is like an LS 3/5A with a larger soundstage presentation, greater dynamic contrasts and SPLs without the "bextrene" coloration in the mids. If you like planar speakers, the open baffle will yield flatter bass response, even bigger soundstage, provide more depth and airy spaciousness at the expense of "snap". But if space is at a premium, you can achieve an "SE amp" friendly speaker system with BBC nearfield monitor quality from this 2 cu. ft. enclosure with the 755A and the 755C/755E with an Altec 3000 or Fostex FT-17H super tweeter.

Below is a sketch of this enclosure's external dimensions:

Building tips:

·        Use 5/8" cheap plywood, the more resonant the better, 1/2" slows down the sound from my experience

·        Do not use MDF, this was not a known cabinet material to the designers of the 755 and other vintage drivers, anyway it is a sure fire recipe for disaster when using any vintage driver

·        Front mounting will probably lessen the midbass bump and the darker mid-range tonality of the "C" and "E" but make sure that the driver is "routed in" so that the front of the speaker frame is flush with the baffle which will provide enough space at the rear for sound to exit through the small holes at the back of the speaker frame

·        If the driver is front mounted, it is no longer necessary to have a "screw on" front or back panel, this way the cabinet will be tightly sealed

·        I have no source for Kimsul but reckon that Dacron polyester fill will be a decent substitute, just line the walls with 1- 2" of this stuff and it should be fine.

Back to Part 1

Visit Joe Robert's Junkyard Jukebox for great WE755A information!

Another site I just discovered with good information on WE/Altec 755s.

WE/Altec 755 Part 1

From Western Electric to Altec

The original Western Electric 8" 755A driver along with the 10" 756A and 12" 728B and 754A were marketed a couple of years after World War II. According to Walt Bender, former publisher of Audiomart and a leading authority and expert on vintage American audio components, the transition from WECO [Western Electric Corporation] towards Altec [All Technical Services division of WECO/AT&T] was not completed until the early 1950s. This was due to a 1930s anti-trust lawsuit filed against the giant telephone company whose business ventures, amongst other interests, included providing sound systems for movie theatres during the booming Hollywood film industry of the pre-WWII era.

Below is an email I received from Steve Schell, manufacturer of Cogent True-to Life Loundspeakers and whose research on vintage American classic speaker components I truly respect. This is probably the most comprehensive and easily grasped explanation of the transition from WE to Altec as well as establishing the [James B.] Lansing connection. Many thanks to Steve for allowing me to upload this information!

May 26, 2006

Hello Joseph,

I just read your 755 pages, after following a link from the Audio Asylum High Efficiency Speakers forum. I recall running across your site several years ago, as well as reading your fine contributions to my well worn and valued copies of the Angela Instruments print catalogs.

There is a little history I can add to the story of the 755. What follows is not authoritative, but based on the reading I have done. Altec Lansing was formed in 1941, after All Technical Services bought Jim Lansing's struggling Lansing Manufacturing Company in Los Angeles. All Technical had been the theatre service branch of Western Electric, which maintained service contracts with several thousand theatres that were equipped with Western Electric sound systems. When the U.S. Government forced W.E. to divest itself of its U.S. theatre sound operations in September 1937, the All Technical branch was purchased for a token amount by several of its managers. They continued to maintain the theatre contracts, though they began running low on replacement parts. Part of the reason for their purchase of Lansing's company was to give them facilities to manufacture the needed parts. They also acquired the designs and production capability of Lansing's theatre systems, regarded by many as being the best at the time. The Lansing product line continued in production, and formed the basis of many of Altec's later sound products.

Western Electric continued to manufacture sound products for numerous applications, but not for domestic motion picture theatre use due to the 1937 consent decree. In about 1940 they began making the 750A, which looks to me like the ancestor of the 755A. It was a 10" driver with an aluminum cone and 4" edgewound aluminum voice coil- please see attached pictures. The 750A is very scarce, and sells for $5000 or more in Japan.

After WWII they introduced their postwar line of speakers, including the 755A, 756A, 728B, 754A, and several phenolic cone variants. W.E. made a huge effort to design the best speakers possible, and to market them effectively through Graybar. In 1949 the U.S. Government intruded on them again and insisted that they cease manufacture of these products. W.E. signed another consent decree at this time. In late 1949 a full page ad in Audio Engineering magazine announced that W.E. was discontinuing manufacture of several of their speaker and microphone models, and that these products would be henceforth be manufactured by Altec Lansing. W.E. had apparently made a deal with their former associates at Altec to manufacture these products and provide W.E. with a portion of them as an OEM. This apparently satisfied the gov't. and allowed W.E. to continue to offer products such as their monitor systems, which contained the Altec-produced components, now labeled with "KS" numbers.

One funny story... I have seen at least two Altec hi fi speaker cabinets from about 1950-1952 on ebay that used shiny perforated metal discs to hold their fiberglass lining in place. Looking closely, I realized that these discs were identical to the metal rear plates on a W.E. 756A. Altec must have received a box of these along with all the other stuff from W.E. and found a use for them.

Altec continued to produce several of the W.E. drivers, horns and microphones through the 1950s. Most of them eventually left the catalog, but a few W.E. designs like the 755 continued to be produced through the 1970s and 1980s.

Apparently the government had good reason to go after W.E. in the 1930s, as they held a majority of market share in the theatre sound business and often acted as a tyrannical monopoly. I'm not sure why they hounded W.E. in 1949, except possibly to try and contain W.E's endeavors to the communications industry for national defense purposes. I have often wondered, though, if the awful performance of most current consumer loudspeakers would have been better if the government hadn't repeatedly driven W.E. out of the business. I suppose we'll never know the answer, but at least we can enjoy some of the surviving W.E. products. I got to hear a pair of 753C monitors recently and they were really something.

Best regards,

Steve Schell

Long Beach, CA

Co-founder, Lansing Heritage web site www.audioheritage.org

---

Altec 755C, Altec 755A and Altec 755E [left to right]

This 8" full range driver has achieved "cult status" amongst audio aficionados. The most desirable version are the ones branded with the Western Electric logo with the frame in smooth silver or textured charcoal greyish brown finish. The mounting gasket always had 5 - 8 quality control stamps showing the tight tolerance procedures excercised in their manufacture. The later Altec branded 755As only had 1 or 2 stamps but essentially looked the same and came finished in either textured charcoal greyish brown or silver hammertone. A lot of silver Altec 755As served as the midrange/tweeter unit in Edgar Vilchur's AR-1 speaker.

Aside from those quality control procedures and alnico magnet, what sets the 755A apart from the later 755C and 755E is the chemistry of the cone material. The procedure was very intensive according to Walt Bender, involving a "vacuum formed" process to produce a cone that contained silk and cotton components. This cone material is also found in original examples of WE/Altec 756A, 754A and 728B. Perhaps this contributes to that beguiling and lifelike midrange quality of a 755A that eludes the later "pancake" versions.

I have seen 755As without the WE or Altec logo but with a KS14703 decal. KS = Kearny Specification, a New Jersey subsidiary which supplied replacement parts for WE. These units may have been represented the final transition period from WECO to Altec. But take note that there are ferrite magnet "pancake type" with KS14703 logos finished in Altec green. These units are really 755Cs and should be identified as such.

Altec 755A

early to mid 50s

[alnico magnet]

Frequency Response: 70-13,000

Sensitivity: 81.5dB/8W/9M

SPL graph courtesy of Steve Schell

Nominal impedance 4 ohms

Impedance graph courtesy of Steve Schell

Typical prices asked for a mint matched pair of WE755s are in the stratosphere, about $3,000/pr. while the Altec 755A go for about 50% less. I never owned a pair of WE nor heard them in the context of my system. But I have heard them in familiar systems and honestly cannot hear much difference between the WE and Altec. Although my impression might change if I start splitting hairs....but I do not want to get into that, through the years I learned that if I can't afford it, I would not think about it.

Altec 755C

Introduced ca. 1961

[ferrite magnet]

Frequency Response: 40-15,000, Impedance: 8 ohms, Sensitivity: 95.5dB/1W/1.2M

In 1961, the "Altec green finish" 755C "pancake" was introduced and the alnico magnet was replaced by ceramic/ferrite. Although the cone looked familiar, the material is diferrent, indicating a move towards 'cost effectiveness'. An additional roll or two was also added to the suspension surround [more compliant] to extend bass response.

This unit was later replaced around 1969 by the slightly less efficient but still SE amp friendly 755E, also with ferrite magnet but the frame is now finished in white and blueish grey combination. The 755C usually came with the surrounds heavily doped, even running and staining the cone itself, whereas the 755E is typically doped sparingly.

Altec 755E

Replaced the 755C around 1969

[ferrite magnet]

Frequency Response: 40-15,000, Impedance: 8 ohms, Sensitivity: 92dB/1W/1.2M

These later versions should not be overlooked because they sound good. Supply is drying up but nice clean units with intact cones show up ocassionally at eBay - 755Cs normally trading from $700-$900/pr. and the 755Es for $500/pr.

I have not come across a modern 8" full range driver that sonically comes close, so they are still worth it in my opinion. Amongst the classics, the only 8" FR drivers I've heard that compare favorably are the rare and hard to find Japanese Pioneer PIM8L OEM for the Lafayette SK98.

The most important consideration when purchasing any of these drivers is to make sure that the drivers are matched! Since they were used in various applications, they may have been electrically damaged or physically abused. Typical problems include partially damaged voice coils. This usually shows up when tested with a DVM, for example the DC resistance reading on my Altec 755A is 2.2 and 2.3 ohms and 6.8 ohms for both 755Cs and 755Es.

At a reasonable price, slight cracks or splits in the cone material can easily be repaired with careful application of Elmers glue and will not significantly impair the sound, if the voice coil is intact. Unfortunately I am not aware of NOS replacement cones for the 755A. There may still be replacement cones available for the "C" and "E" but the availability of original voice coils for these models is also unconfirmed, I have a pair of 755Cs with damaged cones waiting for this procedure.

Here are some 755 sonic impressions from esteemed hobbyists collected from Sound Practices list archive:

Joe Roberts: "Well the 'C' is pretty good. A little bit less high frequency energy than the 755A but good nontheless. More tilted towards the lower mids and a little less crisp than the 'A'.

jc morrison: "by the way, i would also like to add that the later 755s are, in my not always respected opinion, much better than the early ones, which are too peaky for my taste [especially joe's favorite, the really dry cones...] i have heard a lot of 755s. i like the c's and e's crossed over to a tweeter (yegads) in a tapered pipe. these are some of the nicest direct radiating midrange speakers of all times. make a nice pipe drea with a 755C or E, add a focal titanium tweeter: nice, in my book anyway...."

Koji's [of EIFL] translation of Stereo Sound "Tube Kingdom" No. 3 comparison:

Altec 755A - "...reproduces musical sources as it is. The presence of musical instruments is excellent..."

755C - ".....sounds modest but sonic qualities very amplifier dependent. Very good for monitoring the sonic characteristics of amplifiers."

755E - "....also sounds modest, calm, thick and beautiful. Very good for a real audiophile."

WE 755A - "....you feel as if you were embraced with music. Sounds open and brilliant."

Sources and references:

• Stereo Sound Special Issue Volume 1 featuring vintage American speakers.
• Stereo Sound "Tube Kingdom", No. 3 and No. 26
• Walt Bender's "Ask Walt" essays in Audiomart and article on "Olden Goldies" published by The Absolute Sound in the '80s

Go to Part 2 (2 cf box)

Visit Joe Robert's Junkyard Jukebox for great WE 755A information!

Another site I just discovered with good information on WE/Altec 755s.

JE Labs Plinth

Any idler driven turntable should be free from vibration or rumble before building a plinth since a heavy plinth is not a cure for a worn out idler wheel or mal adjustment. 

I used my TD124 for several years on a stock box type plinth and my 301 spent months on a single layer of 3/4" plywood while I made sure it was working up to factory specifications. 

Turntable restoration sites:

Thorens TD124

JD's Garrard 301

Lenco Heaven

JE Labs Rek O Kut Tips

Only then did I avail of the benefits of a heavy plinth which in my experience serve to dampen the last vestiges of vibration from the heavy duty motors employed in idler drive design.

My choice of using layered plywood evolved from my open baffle project wherein I purposely avoided the damped everything approach. Besides I got used to working with the material. ;) I decided to make the plinth 20-30% heavier than the turntable assembly, not very scientific either. ;)

Construction is very simple, it is a sandwich layering [anywhere between 5-7 layers] of 3/4" Birch or Fir plywood boards clamped overnight using hide glue which is the preferred adhesive of violin makers. Using a jigsaw, I cut the first two or three layers based on the mounting template of the turntable and once the proper clearance [depth] is attained I usually leave the two bottom layers solid except at the arm mounting positions which should be pre-determined along with the motor board cutout. 

Fortunately my local lumber yard cut the boards evenly so that the sides square up nicely and only a touch up with a hand plane and sander is necessary to smooth things out.

My 301 plinth 24"W x 24"L x 7 layers of 3/4: plywood

Pictures of 301 plinths built by my SETUP buddies.

Living proof wood veneered MDF also works.

A custom base for a TD124 built using scrap pieces of Philippine Mahogany and other indigenous hard wood glued together. 

Some people claim the best material to build a plinth is using different types of hard wood glued together which is supposedly the Shindo approach in building his plinth. 

Have fun and happy listening!

JE Labs Monaural Playback

Time travelling through the monophonic Hi-Fi era!

One of the fringe benefits of being a freelance musician is travel. I drive close to 20k miles a year and in between rehearsals and concerts I try to make it a point to get to know a new city or town I visit. I particularly enjoy exploring sites that look like it was locked in the 1920s to 1960s timeline. After enjoying Art Deco, streamline and mid 20th century modern architecture, I go to a local diner for a quick bite and then hit the flea markets and thrift stores to hunt for records and vintage equipment. I accumulated several mono LPs and 78s in this manner since I buy records mainly for musical content.

In the past I listened to these treasures using modern stereo cartridges, Stanton 500 or a Grado GTE + 1 equipped with a 78 rpm stylus through a Diego Nardi monophono variable EQ preamp hooked to my main stereo system with the mode switch flicked to mono...nice mellow sound, a bit lacking in dynamics (mostly due to paralleled stereo cartridge coils), very midrange oriented and with 78 rpm discs, accompanied by shellac groove noise. Hi-Fi enthusiasts 60 years ago were already already debating the virtues of triode and pentode output tubes in search for an ideal amp to drive a huge horn loaded speaker using cutting edge driver technology in their quest for better sound.

from "The New High FIdelity Handbook" by Greene and Radcliffe, Crown Publishers, NY, 1956

A typical mid 20th century American high end Hi-Fi set up would consist of a Rek O Kut turntable with a Gray viscous damped transcription arm, a GE RPX triple play cartridge, Fisher 50C preamp and 50A mono amp driving a single Altec 604 duplex speaker with an FM tuner, open reel tape deck and the output from a 20" B&W TV as additional sources. Knowing the capabilities of these classics, there is no doubt in my mind that the sound of this system is formidable. I am aware that there are a few modern day aficionados who maintain that the purest sound can only be achieved from a dedicated mono system.

Some sites to drool over:

My dearly departed friend and inspiration for this project, Brian Clark's mono fantastico! 

Susumu Sakuma (1943-2018) owner of Concorde Restaurant and avid DIYer has been a monaural hifi advocate since the 90s. Watch more Sakuma Videos.  

It is worth noting that stereo evolved from several decades of research and development stemming from monaural sound reproduction. The great recording engineers from the mid 50s who captured the sound cut into the grooves of RCA shaded dog and Mercury living presence as well as other labels like Blue Note, Columbia six eyes and etc., honed their microphone skills in mono.

All these factors inspired me to re-evaluate my approach to monaural playback. Based on my research the starting point is to use a true mono cartridge - single magnet or single coil.

Triple play = 33,45 & 78
GE RPX + GE VRII

Before we proceed to cool gear let's examine the software. During the mono era there were two types of 10" or 12" record formats - LP microgroove and SP coarse groove. In either case the mono signal was etched laterally on both sides of the groove wall. "Hill and dale" Edison discs are notable exceptions. LP = long play (33 or 45 rpm) vinyl and SP = standard play (78 rpm) shellac records that are heavy, brittle, fragile and will break when dropped. Coarse groove SP requires a 3 mil stylus (purists have styli ranging from 2.5 - 4 mil) for proper playback while early mono LPs were cut to playback with a 1 mil. stylus. A .7 mil stylus also works with no danger of damaging the groove but some purists maintain that the smaller profile rides the record groove too low and picks up more noise. I found this to be true only if the record is worn out. It would be safe to presume that any mono LP released after 1967 or thereabouts were cut with narrower grooves and should only be played with a .7 mil stylus.

Aside from the slightly narrower groove width, the reason why stereo LPs can get damaged by using a vintage mono cartridge that does not have vertical compliance is because stereo LPs employ the Westrex 45/45 cutting system wherein the combined stylus motion (horizontal and vertical) is the vector sum and difference of the two stereo channels. Effectively all horizontal stylus motion conveys the L+R sum signal and vertical stylus motion carries the L-R difference signal.

Guide to GE VR stylus replacement

The American GE variable reluctance cartridge was considered state of the art when first introduced in the late 40s. Variable reluctance is a moving iron principle that still exists in modern form in Grado cartridges. A lot of GEs were sold to professional studios and domestic users, thus used samples are still easy to find and affordable. The triple play feature is very convenient to use - flip the red button to switch from an LP to a 78 stylus. "Clip on" replacement styli are still available from dealers at eBay; I use .7mil or 1mil spherical tip for mono LPs and a 3 mil tip for 78 rpm. Cantilever suspension is via rubber blocks (almost rigid) which are not prone to decay but can fall off. Since there is practically no vertical compliance I do not use it for stereo LPs. NOS GE styli are scarce and I use generic replacements.

After hearing the GE l could not go back to a mono strapped Grado or Stanton. But be prepared for needle talk due to high tracking force and lack of vertical compliance. The GE VR cartridge mounted on a viscous damped tonearm has great sonic synergy with the sensuous feel of a cueing lever at your finger tips. The earlier RPX on this tonearm track LPs between 4-5 grams and 6 - 8 grams VTF for 78s; take a gram off in both cases for the later VRII.

GE RPX + Denon DL102

The Denon DL102 is a high output (step-up device not required) moving coil type true monophonic cartridge that can play all types of microgroove format including stereo since it has vertical compliance but no signal sensitivity since it only has one armature. Superb technical information on the DL102 was uploaded by Murray Allen to dispel all the lost in translation issues found in internet forums. A must read! This cartridge was introduced in 1961 for broadcast applications and reissued in 1996 to cater to monaural aficionados. It is a fine cartridge with the familiar DL103 sonics, better tracking ability (3 grams VTF minimum) than the GE VR/RPX but edged slightly in the midrange where the GE possesses an SPU like warmth and transparency. The DL102SD model is for SP/78 rpm shellac playback.

For best performance these 10-13 gram cartridges (DL102 and GEs) require a high mass tonearm like an SME 3012, vintage Ortofon or Rek O Kut, FR64/66, Audio Technica ATP12T, Lenco L-70 or my favorite viscous damped arm.

SPU Mono

For those with Dom Perignon budget yet classic taste Ortofon offers the SPU (Stereo Pick Up) mono which has the motor armatures connected in series and rotated 45 degrees to minimize vertical sensitivity. Even if the SPU mono has vertical compliance it is not stereo compatible because the stylus is 1 mil. The single coil CG25di and CG65di are direct descendants of the 1948 Fonofilm mono cartridge. These mono cartridges are expensive and remain in production mainly due to interest in Japan.

Rek O Kut B12H + Velvet Touch
viscous damped tonearm + GE VR

The RIAA EQ curve was established as the standard EQ for stereo and microgroove record cutting in 1955. Prior to that various EQ curves were used in cutting mono LPs and 78s that was why I built the Nardi monophono circuit from SP 16. This is a good design concept and uses my favorite tubes however I was not too sure about the split EQ time constants which may not be tracking each other accurately for a given curve. The direct coupled cathode follower also made it sound dark and a bit lifeless. I also found myself spending too much time fiddling with EQ rather than listening to music. Initially I was scouting eBay for a Fisher 50C but due to collector interest this unit is priced out of reach for mere mortals. I ruled out the McIntosh C8 and Scott 121 because they use negative feedback EQ. In my audio journey I try as hard as possible not to set design rules but so far any preamp or amp circuit that I encountered employing negative feedback always chokes the sound.

JEL mono preamp with variable phono EQ

After going through my collection of vintage preamp schematics I built a monophonic preamp with passive EQ networks taken from the RCA SV1 preamp which is very similar to my stereo preamp that was based on the phono circuit found at the back of an RCA tube manual. I wanted a period correct project and did away with Ni-mH battery biasing.

As shown in the schematic the standard RIAA/New Orthophonic, AES, Columbia LP and Old 78 passive EQ networks are inserted between the two triode halves of a 6SL7 and selected by mounting them on a 6 position double pole rotary switch. The "Old 78" EQ setting sounds and looks in the scope like it averages various American 78 EQ curves used from the late 30s until the mid 50s with a mild scratch filter that reduces shellac groove noise but still preserves enough top end to 10khz. This might not be compatible with European 78 pressings and do not have any to confirm. I have been enjoying American 78s from RCA, Columbia, Capitol and Decca using this EQ curve.

Even if one uses a vintage tube preamp equipped with a comprehensive EQ selection it is almost impossible to determine exactly what EQ curve was used prior to RIAA standardization, thus the existence of tone controls in vintage units for the user to season to taste. One can get carried away with dialing various EQ curves before playing a record but I would rather live with my four EQ settings sans tone controls and enjoy!

The preamp can be built as a standalone mono preamp with this line stage circuit using a 250k log taper potentiometer for volume control. Cheap carbon track CTS or 250k Alps Blue Velvet will do the job.

Separate chassis CLC power supply with B+ 300-330V @ ~ 10ma. with DC rectified filaments connected via umbilical cord for lowest noise.

SE2A3 + SE10 mono amplifiers

Warm glow of a thoriated filament 

Altec 605B Duplex in a folding open baffle

mono = single speaker

The use of a single speaker was a revelation! Monaural playback is not as simple as flicking the mode switch to mono and hoping for a precise phantom center image. Listening through a pair of stereo spaced speakers introduces phase incoherence that leads to loss of detail and compression of dynamics. There is a wealth of musical information imbedded in the microgrooves of a mono LP. Even the limited bandwidth electrically recorded 78 coarse groove format has information that we have not heard for several years due to improper playback. Pure unadulterated sound - the aural equivalent of B&W images captured by Henri Cartier-Bresson and other fine photographers of that era - with detail, warmth and dynamics to satisfy modern day audiophile requirements. No need to psyche oneself to the illusion of being transported to Carnegie Hall because there is no soundstage to worry about. I now understand why some die-hard mono enthusiasts from the 50s initially claimed stereo was a conspiracy to sell more amps and speakers. The standard achieved at the height of monaural high-fidelity era was great!

Have fun and happy listening!