Building an Ampex MR-70 playback preamp

Options
If this doesn't prove I'm as crazy as a loon nothing will. I am going to try building from scratch one of the most iconic pieces of electronics ever designed. The Ampex MR-70 tape recorder is regarded as the ultimate vacuum tube based machines (only 80 were ever built) in history. It used nuvistors throughout and required 3 years to design and build. I've sent the schematic of the playback electronics to my contact in the Ukraine to see if she can work up a circuit board design. Wish me luck, seriously!

3vte0xh1qkcr.png
«13

Comments

  • pitdogg2
    pitdogg2 Posts: 24,676
    edited January 2023
    Options
    Lost me at "input" :#
  • Clipdat
    Clipdat Posts: 12,656
    Options
  • SeleniumFalcon
    SeleniumFalcon Posts: 3,538
    edited January 2023
    Options
    Some tangible progress. The Ukrainian engineer, Olesia Serba, has been working on converting the schematic to a file that can produce the circuit boards. The first step was for me to select the individual parts I was going to use and send her the lead spacing dimensions. Since I wanted to not use any electrolytic capacitors anywhere the parts would tend to be larger than normal. She has provided a parts outline file:

    uti4d20aksiz.png


    This screen shot was reduced slightly, not to actual scale.
  • SeleniumFalcon
    Options
    Yesterday I received the nuvistor sockets I found on eBay these will be mounted on an external panel.

    fk2r9r3yn1r9.jpg
  • heiney9
    heiney9 Posts: 25,097
    Options
    Very cool. Way beyond my capabilities, but I'll be watching this thread, so lots of pics and explanations.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
  • msg
    msg Posts: 9,591
    Options
    pitdogg2 wrote: »
    Lost me at "input" :#
    I like the bouncy squiggles and seesaw bits.
    I disabled signatures.
  • msg
    msg Posts: 9,591
    Options
    This is gonna be fun to watch, Ken. Looking forward to progress notes and photos, and, ultimately, performance review.
    I disabled signatures.
  • SeleniumFalcon
    Options
    This has, to say the least, been a very educational experience for me. In communicating with Olesia I've had to research the necessary parts and tell her the lead spacing and dimensions and keep track of part numbers so I can order them later. It's also been giving me some small insight into what's been happening in the Ukraine. She'll tell me that the electricity goes off for a while and she can't work on the design. Lot's of appreciation for her efforts.
    It's great how this hobby can create links with other people you otherwise wouldn't meet.
  • SeleniumFalcon
    Options
    Olesia has sent me a schematic drawing she made from the original with connection points to external trim capacitors, variable resistors, potentiometers and the nuvistor connections.

    vv4cvi1u7d3t.png
  • SeleniumFalcon
    SeleniumFalcon Posts: 3,538
    edited January 2023
    Options
    She also sent a file showing component placing that can be printed out 1:1 so I could place the actual components on the surface to make sure everything fits.

    86l3e7ycn33v.png


    There will be two boards for each channel. The yellow squares are the mounting holes for attaching the boards to the chassis.
  • pitdogg2
    pitdogg2 Posts: 24,676
    Options
  • SeleniumFalcon
    Options
    Olivia has finished the two Gerber files needed to build the PCB and she provided some 3D drawings:

    7imyg1inictd.png
    d5n8617hx9g2.png
  • audioluvr
    audioluvr Posts: 5,467
    Options
    You, my man, are certifiable! But most geniuses are. Looking forward to following this!
    Gustard X26 Pro DAC
    Belles 21A Pre modded with Mundorf Supreme caps
    B&K M200 Sonata monoblocks refreshed and upgraded
    Polk SDA 1C's modded / 1000Va Dreadnaught
    Wireworld Silver Eclipse IC's and speaker cables
    Harman Kardon T65C w/Grado Gold. (Don't laugh. It sounds great!)


    There is about a 5% genetic difference between apes and men …but that difference is the difference between throwing your own poo when you are annoyed …and Einstein, Shakespeare and Miss January. by Dr. Sardonicus
  • SeleniumFalcon
    Options
    From my recent drivers license:

    4xfkne3r8yx5.png
  • maxward
    maxward Posts: 1,533
    Options
    I remember the Professor!
  • SeleniumFalcon
    Options
    The company that is making the circuit boards has a way to keep track of the process:

    fehfv2xhhid7.png
  • stangman67
    stangman67 Posts: 2,210
    Options
    What an awesome project! I thought I was handy, you bring it to a whole nother’ level! Seems like you have some very knowledgeable people helping you out as well. Looking forward to following along
    2 Channel in my home attic/bar/man cave

    2 Channel Focal Kanta 3 I Modwright SWL9.0 Anniversary Pre I Modwright PH9.0X I Modwright KWA-150SE I VPI Prime Signature w/ Soundsmith Zephyr MIMC I Lumin U2 Mini I North Star Designs Intenso DAC I Audience OHNO ICs/Audience Furutech FP-S55N and FP-S032N Power Cables/Acoustic Zen Satori I Isotek Sirius
  • SCompRacer
    SCompRacer Posts: 8,367
    Options
    Nice work! Let us know when your manufacturing company goes public. :)
    Salk SoundScape 8's * Audio Research Reference 3 * Bottlehead Eros Phono * Park's Audio Budgie SUT * Krell KSA-250 * Harmonic Technology Pro 9+ * Signature Series Sonore Music Server w/Deux PS * Roon * Gustard R26 DAC / Singxer SU-6 DDC * Heavy Plinth Lenco L75 Idler Drive * AA MG-1 Linear Air Bearing Arm * AT33PTG/II & Denon 103R * Richard Gray 600S * NHT B-12d subs * GIK Acoustic Treatments * Sennheiser HD650 *
  • Jetmaker737
    Jetmaker737 Posts: 1,015
    Options
    the skillset to do something like this is rare indeed. It's a pleasure to watch. Kind of like watching a superhero movie where you're thinking to yourself "I wish I could do that"!
    SystemLuxman L-590AXII Integrated Amplifier|KEF Reference 1 Loudspeakers|PS Audio Directream Jr|Sansui TU-9900 Tuner|TEAC A-6100 RtR|Nakamichi RX-202 Cassette
  • SeleniumFalcon
    SeleniumFalcon Posts: 3,538
    edited February 2023
    Options
    Most of my inspiration comes from having champagne taste in audio gear but tap water budget. I figure if I can read about something and understand how it's done then maybe I can build it. If anybody wants help making a crossover PCB for a speaker or anything else let me know and I'll help.
  • pitdogg2
    pitdogg2 Posts: 24,676
    Options
    You're a rare breed Ken!
  • SeleniumFalcon
    SeleniumFalcon Posts: 3,538
    edited February 2023
    Options
    One of the choices in getting a circuit board made is the thickness of the copper traces: either 1 ounce or 2 ounce. The copper thickness of 2 oz copper is 2.8 mils (0.0028"). 1 oz copper thickness is 1.37 mils (0.00137"). The idea is that the thicker copper is more suited to circuits that handle more current (speaker crossovers, for example) and less copper is needed for smaller signal handling. The 2 ounce copper is a bit more expensive and can add to the wait time, but I went with the 2 ounce choice and it didn't delay the production that I could see.
    I believe there is even thicker traces available (up to 20 ounce), but that wasn't offered in the choices available.
    Post edited by SeleniumFalcon on
  • newbie308
    Options
    "Selenium Audio Kits" sounds like a cool business name...
    Sources: Technics SL1200MKII | SME3009 Tonearm | Monster Alpha 1 MC cartridge | Oppo UDP203 disk player | Nikko NT-790 analog tuner | Musical Fidelity Trivista 21 DAC | Preamp: Threshold SL-10 | Amplifier: Threshold Stasis 2 | Speakers: Snell Acoustics C/V | Kimber 12-TC bi wire speakers | Analysis plus Oval 1 preamp to amp | Wireworld Eclipse 7 DAC to Preamp | Wireworld eclipse digital IC Oppo to DAC | Audioquest Quartz tuner to preamp |
  • SeleniumFalcon
    Options
    Some parts are starting to arrive, the circuit boards (I wish they were the same color, but the undersides are, not the component sides). Some of the necessary nuvistors have posted, 5 from Turkey (I checked with the supplier and he is okay, nowhere near the devastated area) and some from the US. The 7895 is near to impossible to find, but the 6CW4 is the identical device with, perhaps, an increased sensitivity to microphonics. I've found enough of the 7895 for the first and second positions in the design and I'll use 6CW4 for the rest. I've been lucky to find NOS of them. The 7587 came from Turkey and are unused, these are tetrodes and along with the output transformer form the balanced output stage.

    5hpqu8cje0sj.jpg
  • pitdogg2
    pitdogg2 Posts: 24,676
    Options
    Ken how long do those super tiny nuvistor tubes last?
  • SeleniumFalcon
    Options
    The lifespan is given as 100,000 hours, of course there are variables. The worms that will munch on my carcass will have evolved to travel in space and the nuvistor will still be good.

    gdmwqs5ctjjl.png
  • pitdogg2
    pitdogg2 Posts: 24,676
    Options
    I kind of figured they would outlast both you and I. Exspecially since the R2R will not be used like it would have been back in the day. :D:D
  • tonyp063
    tonyp063 Posts: 1,051
    Options
    Ken,
    Out of curiosity, who are you using for your board fabricator?
    I like the looks of those much more than the usual suspects.

    I continue to enjoy & be fascinated by your threads. Thank you.