JE Labs Arkiv (up to 2008): June 2012

Saturday, June 30, 2012

Hammond 125ESE Part 1

Hammond 125ESE

For years I have been searching for a truly affordable SE OPT that is flexible enough for experimentation with various triode output tubes. Last year I found a DIY SE2A3 amp project featured in MJ 2/00 using a Noguchi universal OPT [pri.Z = 2.5K, 3.5K and 7K], the PMF10WS for JPY 6,800. They even have a lower priced model, the smaller, PMF 6W for JPY 3,500 for people who want to build an amp around a 71A or 112A. Unfortunately they do not export and their fax no. specifically states "not used overseas". This is a clear indication of a well developed market in Japan that caters to the audio hobbyist that makes it unnecessary for manufacturers and dealers to look beyond their shores to thrive.

Even if the SE/DIY revolution in the USA started in the early 90s, the availability of a true high-fidelity airgapped SE OPT for under $100/pr. is practically nonexistent. This could be one of the main reasons why in such a huge and progressive country, proportionately, the number of audio/DIY enthusiasts remain small.

The Audio Note UK "experimenter series" at $75/each was a pretty good performer but has been unavailable for quite a while and it still would have cost over a hundred bucks for a pair. The early Hammond transformers I tested [125E and 1627SE] back in '97 had some issues that fell short of my expectations. Although the 1627SE had pretty good bass extension [due to the massive laminations], the upper midrange to high frequency was very rough, whereas the 125E without an air-gap just didn't have anything below 150Hz with more than 20ma. of DC unbalanced current flowing and forget about the upper range. But that was 4 years ago and I am well aware that the 1627SE is a popular choice for satisfied builders of my SE 300B project while the 125E is a favorite for my Simple 45/2A3 and Bob Danielak's Darling SE 1626 [Sound Practices 15]. I can just assume Hammond has improved the performance of these products based on the market success of these models.

By chance, I stumbled by the new air-gapped 125ESE at $35/each while surfing Angela Instruments' website. After some deliberation I whipped out my credit card and ordered a pair. I also took the chance to say hello to Steve since I have not seen him or the shop for almost two years. Within a day or two they arrived at my doorstep. The 125ESE is an open frame unit weighing a little over 3 lbs and uses M6 silicon steel laminations according to the data. It is indeed twice the size of the original 125E but instead of solder tags, it came with long color coded leads.

Here is a picture of the 125ESE beside a Tango U808 for size perspective. It actually reminded me more of the Tango U708 in terms of size and weight.

detailed specs

The primary is adjustable between 2.5K, 5K and 10K and claimed to handle 80ma. of DC unbalanced current. There was no data on inductance [relevant for bass performance] but it looked promising enough despite my reservations about cosmetics.

I installed them [2.5K mode] on my current test mule, a stereo SE2A3 [schematic below] amp to play background music in my second system and had the surprise of my life because I was actually hearing music and found myself spinning various LPs and CDs. After a while I noticed one channel had a very slight tendency to spit out sibilance in the upper frequencies and confirmed it by switching cables between channels and it remained on the same side.

The amp was taken to my test bench for basic power output, frequency response measurements and I injected square waves to see how the OPTs were behaving. Sure enough OPT 2 had a slower rise time, an overshoot and some ringing at 10kHz, even at 1kHz the overshoot is quite evident [not a good sign].

OPT 2 @ 10kHz

OPT 2 @ 1kHz

However OPT 1 at 1kHz and 10kHz compared favorably with the Tango U808.

OPT 1 @ 1kHz

OPT 1 @ 10kHz

Tango U808 @ 1kHz

Tango U808 @ 10kHz

[Note: top trace is the input signal from the audio generator and bottom trace is the amplifier output].

In spite of my reservations about OPT 2, the 10khz performance was still better compared to the early '97 1627SE and significantly better than the 'ungapped' 125E across the entire audio bandwidth.

Obviously, what I heard [and confirmed on the scope] was a serious mismatch between the two 125ESEs, that is why it can be detected through critical audition. If I had two identical units like OPT 2, I would not have detected the anomaly, although I surmise that the sound would not be as clean as having a pair that measured like OPT 1.

I brought the amp to NYC so that my friend Ding can offer another perspective and I could also hear them through 604-8Gs. He was very impressed and thought they were great value for the money although he did mention hearing something slightly funky about the high frequencies on one channel. On some material he found it more extended but on other tracks it sounded a bit rough. But he qualified that it was not really very apparent and only noticeable when he listened for it. He also made me promise to bring the amp on my next NYC trip because he really liked it. Meanwhile I had already emailed Steve requesting for another pair of 125ESEs because of my earlier findings and wanted to get a handle on quality control. By the time I returned home, the package was already in my apartment.

The first pair was replaced by the second pair. I turned on the amp to play background music for about an hour and then started serious listening evaluation in my main system with the Altec 2-way speakers. I used another SE2A3 amp with Tango U808 OPTs as a reference point. The circuit is virtually the same in both amps with bi-plate 2A3s running at 18W plate dissipation and the U808 set to 2.5K mode [usually set to 3.5K, but I wanted to limit variables]. I listened to a variety of music ranging from LPs by Sinatra, Ella, Billie, jazz/big band, 80s pop/new wave, to Mahler sym. # 5, Bartok concerto for orchestra, Mozart string quartets, Ravel piano trio and DAT masters of live performances I recorded.

Do not be discouraged by the specified +/- 1dB, 100Hz-15kHz bandwidth because it was easily exceeded in my listening evaluation and test bench measurement results. I could hear down to 50Hz, perhaps the fundamental was already rolling off but the bass note overtones [harmonics] were right, which is very important to hear good bass definition. The U808 offered more air and space indicating a higher bandwidth ability and gentler treble roll off, it also sounded more controlled and composed in the bass. If I was to nitpick, I would say that the U808 has the edge in the ability to resolve detail and more transparent overall with a slight tendency to sound dry and clinical. In spite of a bit more grain across the audio spectrum, the 125ESE always delivered the emotional impact of any pre-recorded material. This is what I deem as high-fidelity in the true sense of the word, honoring the music. The relative lack of transparency will not be apparent unless the units are pitted against superior and more expensive units.

Assuming OPT 2 was a fluke, I give the 125ESE my highest recommendation. It should not take that much time nor effort for Hammond to keep quality control within the standards set by OPTs 1, 3 and 4 while keeping the same cost. Based on the impressive performance noted, the 125ESE deserves metal shrouds to cover the core even if the 2 - bolt mounting tab arrangement is kept. This way it can be painted giving DIYers some flexibility with aesthetics. I also no longer endorse hacking PP OPTs from vintage tube integrated amps for use with my Simple 45/2A3 project; the 125ESE will perform much better in this application.

If I had the time I will not hesitate running 300Bs with these transformers. But watch the current, even if it is specified to take 80 ma. the core may still saturate [just a hunch, based on the 100Hz square waves I saw], you may be better off backing down to around 60-70ma. For those who really prefer their 300Bs hot, the 1627SE is a safer bet and will assure greater bass extension.

Given the performance and flexibility the 125ESE offers at such modest cost, it should bring the joy of SE DHT amplification to a wider audience and the unavailability of affordable OPTs is no longer an excuse not to build your own SE amp. Place your order for 125ESEs at your favorite dealer so that Hammond will continue improving their products and come out with quality transformers like the 125ESE for DIY enthusiasts. While you are at it, snap up the remaining American made 2A3s, 50s, 45s, 10s/VT25s, 71As before they dry up and watch out for vintage paper cone alnico drivers, because you will need them.

Go to Part 2

Hammond 125ESE Part 2

Test bench results for the Hammond 125ESE

[Tango U808 used as a reference point]

Foreword

"Reflections of a scope jockey"

These tests are by no means definitive and I still rely on my ears more than anything else. However the techniques I employ have served me pretty well as short cuts in troubleshooting.

Although some tonal aberrations can be recognized on the scope, it should not be taken as the last word. I have tested amplifiers that looked good on the scope but failed to satisfy me musically or two amplifiers with dissimilar circuit topologies that looked and measured the same but sounded totally different from each other. But these were mostly amps with a lot of negative feedback. Negative feedback can extend the bandwidth of an "ill conceived" circuit or output transformer while overshoot and ringing at high frequencies can be "cured" by judicious use of picofarad value caps. So keep these "band-aids" in mind.

I passed up on several opportunities to purchase a good harmonic distortion meter cheap at hamfests, mainly because I do not think it has anything to do with music. On page 32 of the Radiotron 3rd edition, I quote, "The total harmonic distortion is not a measure of the degree of distastefulness to the listener and it is recommended that its use should be discontinued", this was written by someone in 1938 and knew better then.

To a certain degree measurements can be helpful just like what you will see in the case of unit # 2. I also take measurements and observe the behavior of recently completed amp/preamp projects to make sure the circuit is functioning properly. As long as the waves look clean and the math [operating point and etc.] works out right then the unit is ready for an audition.

In the following, all transformers were installed and tested in SE2A3 amps with the same 76-DC-6SN7 input/driver circuit cap coupled to a 2A3 running at 17-18W plate dissipation [60ma. DC unbalanced current through the primary] with no NFB [negative feedback] employed.

Frequency response in 2.5K mode @ 1W output into an 8 ohm load [0 dB = 1W]

Hammond 125ESE [all dated 02/27/01]

Unit # 1: 20hz - 20khz = flat +/- 1 dB, @ 50khz [ -3.5 dB], rolloff is smooth.
Unit # 2: 20hz - 20khz = started rolling off at 10khz [ -.3 dB] @ 50khz [-6 dB], rolloff is rough
Unit # 3: 20hz - 20khz = flat +/- 1 dB, @ 50khz [ -4 dB], rolloff is smooth.
Unit # 4: 20hz - 20khz = flat +/- 1 dB, @ 50khz [ -3.5 dB], rolloff is smooth

Tango U808 [2.5K mode]:

Both units: 20hz - 20khz = flat +/- .5dB, @ 50khz [-3 dB], rolloff is very smooth.

NOTE: Typically the bandwidth of any "universal" type output transformer will diminish when used to step down at the secondary taps. So expect less bandwidth at 5K and even more at 10K primary Zs. However, I do not think this would have any serious sonic consequence in the case of the 125ESE units 1, 3 and 4.

Hammond 125ESE square wave response at 100hz, 1khz and 10 khz

Top trace is the signal from the audio generator at less than .1V rms and the bottom trace is the amp output at around 2.2V rms into an 8 ohm load.

OPT 1 @ 100hz

OPT 1 @ 1khz

OPT 1 @ 10khz

OPT 1 - looks good overall!

OPT 2 @ 100hz

OPT 2 @ 1khz

OPT 2 @ 10khz

OPT 2 - the spike at the leading edge of the 1khz square wave is a manifestation of the harshness heard in the treble. At 10khz the rise time is comparatively slow compared to the other 3 units. The overshoot is an artifact of that seen @ 1khz. a slow rise time tend to curtail transient signals resulting in poor treble resolution.

OPT 3 @ 100hz

OPT 3 @ 1khz

OPT 3 @ 10khz

OPT 3 - slightly slower rise time at 10khz compared to OPT 1 and OPT 4 but still fine. There is a tendency to ring but it is well damped. These slight aberrations were not detected by my ears and sound identical to OPT 1 and OPT 4.

OPT 4 @ 100hz

OPT 4 @ 1khz

OPT 4 @ 10khz

OPT 4 - almost as good as OPT 1 except for the slightly rounder leading edge at 10khz. All four 125ESE units showed greater tilt at 100hz compared to the U808.

Tango U808 @ 100hz

Tango U808 @ 1khz

Tango U808 @ 10khz

Tango U808 [both units looked identical] - less "tilt" at 100hz [greater inductance?] compared to all the 125ESEs and may well be the reason why the bass sounds more articulate and extended. Tango had tight quality control procedures based on several models and samples I've tried.

Back to Part 1

Sunday, June 24, 2012

Shop Talk

JE Labs test bench

(ca. 2000)

From right to left: Genrad W5MT3A Variac, Tektronix 2205 20MHZ dual trace scope, Weller WTCPS soldering station, second shelf - right to left: Heathkit IM21 ACVTVM, Leader LAG27 sine/square wave audio generator, Eico 260 AC/VTVM. Hand held DVMs - Fluke 8060A true RMS, Testmate LCR 195 capacitance/inductance meter and Fluke 75 DMM

In retrospect

My first exposure to high fidelity equipment was at The Juilliard School. I entered the pre-college division n the late 70s and the record library/listening room was equipped with at least a dozen Thorens TD150AB, with Shure M7D, Shure phono preamp/headphone amp driving huge Koss headphones as well as a couple of Tandberg reel to reel tape decks for archive tapes while the classrooms had TD124, Shure M3D, Dynaco SCA35 integrated amp driving AR2A speakers. I spent a lot of free time listening to my favorite recordings which was a crucial part of my musical development aside from practicing and attending concerts at Lincoln Center, Carnegie Hall and other venues in the city.

By the early 80s, I was an undergrad and had an apartment. With some spare change I assembled my first stereo system which consisted of an original AR turntable with a Grado GTE+1 hooked to a NAD 3020 driving DIY speakers with components from Radio Shack.

While the school upgraded their vintage equipment to Denon direct drive turntables, CD players, integrated amps and Sennheiser headphones, I removed the jumper wires from the 3020 to drive a Dyna ST35.

One day while taking a break from practicing I read an article in Fanfare magazine written by Robert Fulton, "Prerequisites for Capturing the Musical Experience" and his description of directly heated triodes left an indelible impression.

My financial status improved in graduate school with a better scholarship grant and concert opportunities that afforded me to purchase used high end gear - conrad johnson PV2Ar preamp, Berning EA230 amp driving Magnepan SMGa speakers.

Given my inclination towards DIY, I purchased the Merrill mods for the AR turntable. Then I mounted a Sumiko FT-3 tonearm and a Grado Signature 8MX cartridge. A SOTA acrylic mat + reflex clamp gave it more high end credibility.😉

My power amp was the Berning EA230, a 30wpc tube amp using 6JN6 beam power tetrode loaded by surplus Scott output transformers using a Williamson derived octal driver tubes (6SN7). On hindsight it was a good sounding amplifier but did not have the transparency of the directly heated triodes discussed by Fulton as I was about to find about a few more years later. It was powerful enough to drive Magnepan SMGas in my tiny NY apartment. But as I got to know these speakers it became apparent that despite the lack of cabinet colorations the midrange was veiled and the low sensitivity limited dynamics.

As an experiment I bridged my back up Dyna ST70 and another ST70 from a friend to drive the SMGas and the improvement with 70W of EL34 pentode per side was not significant. This system sounded fine playing audiophile recordings but it was not at all satisfying when listening to recordings that have meritorious performance.

The SMGa was eventually replaced by Rogers LS3/5a. After a trip to the factory and incurring an expensive repair bill, I unloaded the conrad johnson and Berning I reverted to my back up and hacked Dyna electronics - PAS/ST70/ST35.

I stopped subscribing to Stereophile and TAS after the Walt Bender and Steven Stone articles on "olden goldies" and spent my spare time at the Rodgers and Hammerstein Archives of recorded sound on the top floor of the Lincoln Center Library which has an extensive collection of audio periodicals. This is where I found early tube/DIY publications The Audio Amateur and Audio Update by Audio Dimensions of San Diego, CA which also published Tu-be or not Tu-be.

While my audio buddies where raving about their latest recommended components, I was studying schematics and collecting classic tube equipment from Acro, Dyna, Eico, H-K Citation, Heath, Lafayette, Paragon, Pilot and etc. no Marantz or McIntosh, those were expensive even then.

I frequented what was left of Radio Row around Cortlandt street and also perused the surplus stores along Canal street for parts and tubes. I must have done every PAS modification published in that era as well as grafting every classic input driver/phase inverter circuit that intrigued me, onto my ST70 test mule. I kept a Paragon E-1 preamp in stock form as a reference for my PAS hacking experiments because the cascoded 12AX7 front end had a 3 dimensional midrange I never quite achieved until I reverted to using octal based 5691s/6SL7s for phono.

By the late 80s I was happy with a much modified PAS preamp powered by a Heathkit tube regulated power supply, a pair of Dyna MKIVs with GSI input boards and EL34s strapped in triode or an upgraded Eico HF87 also strapped in triode driving LS3/5As.

The AR/Merrill front end stayed constant since it was not put to shame compared to a Linn LP12 Valhalla Ittok combo. My back-up turntable then was a TD124 which I found for $1 at an antique auction, it had an Ortofon SMG 212 which I foolishly sold for a song and replaced with a Sumiko MMT arm. Deep inside I knew it sounded better than the AR/Merrill but I was in denial since it had no audiophile credibility.

Concurrent with the LS3/5A, I also owned Quad ESL 57s which I found to sound best driven by classic PP EL84 amps I had in my "prized" collection then - Acro 20/20, Dyna ST35, Leak 20 and Pilot SA232, but I gave up the ESLs due to panel reliability and rectifier block issues.

The early 90s was a turning point, I became a customer and friend of Steve at Angela Instruments. Eventually I started working part time in the shop servicing countless classic tube equipment and Audio Note, UK kits. I attended hamfests and radio shows, met Joe Roberts and instantly became a supporter of the then fledgling Sound Practices magazine.

JE Labs/Mullard PP2A3

My first DHT amp was a PP2A3 with a Mullard type input/driver circuit utilizing 6SL7s and 6SN7s, Peerless 16309 OPTs 7W of pure Class A driving Spendor LS3/5a, it didn't go loud but it was so much more transparent than any of my previous efforts. As I went through the mid 90s, I disposed my classic tube amp collection, LS3/5A, AR/Merrill and other vestiges of high-end gear to finance acquisition of Tango and Tamura iron, parts, idler turntables, vintage Altec drivers and wrote a Homebrewer article for SP17. It was an idealistic venture that was destined to remain underground yet had a significant impact on how we view the audio hobby these days.

Tube basics and books

A tutorial or basics chapter in these pages is beyond the scope of my abilities since I developed my skills during pre-internet days almost empirically - through trial and error with the help of reading books, schematics and talking with old timers. A google search will yield websites that will address these concerns. But I recommend to every potential DIYer to acquire a copy of the RCA tube manual and read through the first few pages to get a basic idea of how a vacuum tube operates and read schematics. Another much overlooked book of great basic resource is the Radiotron 3rd edition which contains comprehensive information for anyone who wants to dabble with single ended and push-pull triode amplification as well as preamplifier circuits and power supplies without having to deal with the complex mathematical equations and in-depth discussion of theory found in the 4th edition.

DIY magazines

Since the demise of Sound Practices the only DIY oriented magazine published in the USA is Audio Xpress, occasionally they have articles of interest to Single Ended Triode amp and High Efficiency speaker enthusiasts. Vacuum Tube Valley also went with the tragic loss of Charlie Kittleson. Japanese publications like MJ Audio Technology and Stereo Sound Tube Kingdom are great. Even without much knowledge of the Japanese language I am able to get ideas by looking at the schematics and high quality illustrations. The Sound Practices Magazine Archive CD is a must have. This is the official CD edition and beware of bootlegs.

DIY Tips

Design Philosophy

As much as possible I do not like making rules for myself since it limits my ability to explore new ideas. However in the projects below you will notice that I do not use negative feedback in my electronics because I have not found a design that employed any form of global negative feedback that sounded good to my ears. Some people swear by cathode followers others swear at it. I take the middle road on this particular topic because I found the addition of a cathode follower at the output of a line stage to be sonically beneficial in some cases but not at the output of my phono stage. My non technical explanation as to why a cathode follower does not sound good at the phono output is because the signal is still below 1 volt and the cathode follower being a 100% regenerative form of local feedback affects the purity of the signal. I only use a cathode follower in this position in severe cases like driving a sound card to transfer LPs to CD-R. For critical listening I do not use it.

With speaker crossovers I also take simpler is better approach and have yet to find a better sounding design than a simple 1st order 6dB/octave with L-pad attenuation to match sensitivity between drivers.

Chassis layout

This is very basic and if you look at the various pictures of preamps and amps in these pages you will notice that I place the power supply as far as possible from the audio circuit in power amps and use a separate chassis for the power supply in preamps. With regular unpotted iron, I orient the core of adjacent iron [chokes, power and filament transformers] so that the laminations "cross" each other. According to the Radiotron Designers' Handbook this prevents magnetic induction. Some people claim that they do not hear improvement in reduced noise or hum nonetheless it is good engineering practice.

Operating Points

The bulk of inquiry I get regarding amp projects is power transformer substitution especially from newbies. This is why I try to use power transformers from the Hammond Catalog as much as possible. Please note that adapting another power transformer may involve a redesign. So I'd appreciate it if people can be reasonable.

I was so impressed with Herb Reichert's Flesh and Blood amp (Sound Practices Issue 8) playing in a friend's system that I decided to build a clone. But I did not have the power transformer Herb specified and was disappointed with the sonic result I got from my copy. This is how I discovered the utmost importance of keeping the operating points in creating the sonic signature of an amp since the power transformer and power supply design comprise the heart of a tube circuit.

All the projects listed below use readily available power transformers. Please make sure you follow the circuit diagram and especially if you are a newbie, stick to the power transformer specified in the schematics to insure that you are hearing a JE Labs circuit. If you do not follow my operating points, it is no longer my design.

Signal path

Nowadays I only use paper in oil - Vitamin Q and Russian K40Y/K42Y - or equivalent capacitors for signal coupling and carbon composition [Allen Bradley or Riken] for plate, cathode and grid loading. I use of cement or wire-wound [preferably non-inductive] resistors for output tube cathode bias. These materials do not have the zippiness inherent in plastic [polypropylene, polystyrene, mylar and etc] type caps or grit I find in metal film/oxide resistors. The cheap Asian OEM carbon film resistors available from Parts Express are good too since Allen Bradleys are hard to find in bulk and Rikens tend to be expensive. Try to buy in reasonable quantities so that you can match to close tolerances as possible. It is also worthwhile over rating carbon resistors to make them more stable. Using these type of parts is just second to operating points towards achieving the sound I am searching for.

Cathode bypass

I can justify the use of Black Gate or Cerafine in this position, however if you can no longer find or afford them, Sprague "Atoms" are good replacements at a fraction of the price.

Power supply caps and dropping resistors

Paper in oil 'can type' are ideal but normally not very practical due to chassis space so I use decent electrolytics from Sprague 'Atoms', Cerafine, LCR and even the OEM cans that Angela Instruments and Parts Express sell for reasonable cost. Inductive cement or wire-wound resistors are at their best in power supply application because the additional inductance help smoothen AC ripple.

Wire

I use Kimber TCSS bought in bulk because of the high purity copper and insulation which does not melt easily when soldering. In my more deluxe application I even tried Kimber AGSS [silver] but found that 19 gauge 99.99% solid silver covered with teflon tubing to do just as well. I don't practice any religion with wires, cables and interconnects so any good quality insulated conductor of appropriate gauge should do the job. There is nothing wrong with NOS cloth covered wire as long as the conductors are not corroded.

Boutique parts, tube rolling and etc.

I have received numerous emails inquiring about, what is best? The bottom line is, there is no such thing as "the best". A good sounding system is the sum of all its parts working together by reinforcing and negating its own strengths and weaknesses. Using tantalum resistors, silver foil caps, controlled substance wire, power supplies weighing a ton and exotic metal alloy output transformers will not guarantee musical satisfaction, synergy between components in a well designed circuit is the vital issue in assembling a musically rewarding audio system.

My recommended parts are in no way an endorsement of the best they just sound good to my ears, that's why I use them. It would be fair for others to disagree, but why should we indulge in an endless debate if the ultimate goal is to enjoy music?

Same thing with tubes, I've built and experimented with several circuits through the years and you will find in these pages that I favor Art Deco era 5-pin triodes - 227, 27, 56, 37 and 76s; octals - 6SL7/5691 and 6SN7s; and directly heated flea power triodes - 300B down to 71As. These are tubes that were specifically designed for audio amplification. There are slight sonic differences between, e.g. - 6SN7s but proclaiming which type is best is an exercise in futility, my preferred driver and preamp tube types are listed in each project, so if you substitute a flavor of the month tube that I did not endorse and disappointed with the sound, you know why....

Once you indulge in DIY you will hear that circuitry and operating points make more of a difference than the latest tweak in fashion. Collect your favorite sounding tubes and build around their virtues.

Have fun and happy listening!

Rek O Kut Tips

....vintage studio equipment in a scene from "The courtship of Eddie's Father", starring Glenn Ford..

Not much information can be found in cyberspace about the original Rek-O-Kut company based in NYC. But the company was a highly regarded manufacturer of turntables, tonearms and cutting lathes during the golden age of Hi-Fi. A lot of these idler driven turntables found duty in radio stations due to their quick start up time, stable speed and simple yet well executed engineering. My 1961 Lafayette catalog lists several idler models starting with the entry level 2-speed 4 pole induction motor driven Rondine Jr. L-34 [33 and 45] and L-37 [33 and 78], 3 speed Rondine B12 with same 4 pole motor as the L-34/L37, Rondine Deluxe B12GH which uses the Papst "flywheel" hysteresis motor and the the top of the line B12H which uses the HUGE hysteresis motor [see picture below]. By 1963 the L-34/37 Rondine Jr. series was replaced by the N33/34H belt drive which usually was fitted with the Papst motor. I have no experience with these models or motor but they have a good following.

All the Rek-O-Kut turntables are a model of engineering simplicity [no pitch control or eddy current brake] making the Garrard 301/401 and Thorens TD124 look over engineered. The motor and idler wheel arm assembly are individually isolated through rubber grommet mounts to prevent extraneous vibration from reaching the platter. The control switch physically moves the isolated motor with stepped capstan to engage the idler wheel at a chosen speed. Surprisingly the budget Rondine Jr. model employs dual idler wheels, the compromise being a simpler idler wheel arm assembly that does not need to be moved up or down to engage the capstan. Building a massive plinth for this model is very easy since it only requires a rectangular cut out to accomodate the motor unit. Due to the simple design the condition of the idler wheel[s] and rubber isolators as well as the few lubrication points have to be addressed to insure optimum operation.

The spindle is approximately 5/8" in diameter and comparable to those found in a TD124 or 301/401. The platter is a precision lathe turned aluminum weighing about 5-6 lbs. depending on the vintage [earlier models were lighter].

Pull out the platter and then remove [3 screws] the bearing well from the motor board. The inner rim of the platter and spindle should be cleaned and the bearing well should be flushed with lighter fluid or denatured alcohol. There should be a small ball bearing inside the bearing well. Inspect the condition of the ball bearing and if it shows signs of corrosion, replace it with a 1/4" or 5/16" ball bearing available from a bicycle shop. A brand new shiny ball bearing insures a smooth and silent turning platter. I am not sure what the original diameter of the ball bearing was but find that a 1/4" seems to turn a bit quieter than the 5/16" and the platter rests quite low on the top chassis which looks just like in the original brochures.

The motor assembly can be removed from the top chassis by unscrewing the switch knob [1] and the 3/8" hex nut on the opposite side [2]. Now is the time to check the condition of the rubber mounts [1& 2 below and two more on the other side not visible] 4 of these are used to isolate the motor. If they are pliable and free from cracks just clean up all the grease and accumulated gunk. Replacement rubber grommet mounts are still available from Lord Corporation in Erie, PA although I have yet to encounter cracked or glazed rubber mounts.

After years of storage the top and bottom motor bearings' lubricant may have gummed up. Spray Electric Motor Cleaner and compressed air into the oiling turrets [marked with arrows]. Once the bearings are turning without significant resistance, light oil can be added.

To clean the idler wheel bearing remove the E-clip and flush the stud [1], brass bearing [2] and washers with lighter fluid. For reassembly the sequence [from bottom to top] is - thick washer, thin washer, idler wheel, thin washer, thick washer then E-clip. I use thin gun oil to lubricate the stud and brass bearing.

Idler wheel condition is very critical for a quiet running ROK. Minute flat spot[s] in the idler wheel will definitely be heard as loud rumble. It has been suggested in the Vinyl Asylum that cleaning the rubber with lacquer thinner can rejuvenate a "not so tired" idler. With the platter off, turn on the motor and engage the idler while brushing the rubber wheel with a small paint brush dipped in lacquer thinner. Sometimes this trick will work but if the rubber hardens and becomes noisy when it dries up, it needs to be refurbished. It didn't work on this particular idler wheel set.

Worn out idler wheel - the rubber is glazed and hardened, it also measures 1/32" less than 2.5"

Refurbished idler wheel is exactly 2.5" in diameter

The turntable is now almost as quiet as my Garrard 301. Mechanical noise should not be audible 4 feet away from any idler driven deck in a quiet room. Another way to determine a worn out or glazed idler wheel is to try grabbing the platter and if it stops easily or does not offer much resistance the rubber is slipping.

According to the manual SAE 20 motor oil is the recommended viscosity for the main bearing. I use non-detergent SAE 30 and you only need to pour in enough oil to cover the top of the ball bearing and then rubbing some to the spindle before inserting the platter into the bearing well. As pictured the tip of the 1/4" bearing I used is not quite submerged in oil and needs a couple more drops.

This picture shows the position of the set screws with rebuilt idlers installed and speed calibrated. Although there is no pitch control in most ROK models, speed can be fine tuned by moving the set screw along the arrow marked directions. The motor should have been running for at least 15 minutes before adjustments are made. In general it would be prudent to keep the idler to rim tension at a minimum [closer to the knob] to prevent premature idler wear. Too much tension with good idlers slow down the speed and generate more noise. Proper tension is obtained when the platter locks in to speed within a couple of minutes. I use a neon pilot lamp from Radio Shack soldered/heatshrink wrapped to a long AC cord to view the stroboscope markings.

Other Models

Rondine Jr. L-37 and LP743 - 3 speed

These are very similar in design but the earlier LP743 has rather innovative features - the same idler is used for 33 and 45 and the mechanical switch to the extreme right changes the height of the idler to match the 33 or 45 rpm capstans of the motor. The idler on the left is exclusively a driving wheel to spin [no contact with the motor capstan] the platter at 78 rpm. However the idler arm on the LP 473 is directly attached to the top plate so the idler is rigidly in contact with the inner rim on start up whereas the L-34/37's idler arm is mounted on a substructure isolated by 3 rubber grommets contributing to less mechanical noise but a tad less kick on start up.

The bottom idler wheel [marked with an arrow] is driven by the bottom capstan [78 rpm] in the motor shaft which then transfers the motion to the top idler wheel to turn the platter. This pair of idler wheels for 78 rpm are mounted using set screws instead of an E-clip. The platter on the LP743 is slightly smaller and a bit lighter but the main bearing dimension and quality are identical. Earlier versions of the Rondine Jr. L-34 or L-37 also used this square type motor.

Idler wheels are not interchangeable between the B12H, LP473 and L-34/37.

Rondine Deluxe B12H fitted with a ROK S220 Gyropoise tonearm. This is the top of the line 3 speed model using a single idler wheel. Notice the tool kit under the platter?

The tools are provided to fine tune the speed and idler tension - the Allen wrench is used to remove the big control knob and the hex wrench to loosen the hex nut to fine tune the speed. As you slide towards 2 there is greater tension. Apply the same adjustment procedure as noted in the Rondine Jr.