Building an Ampex MR-70 playback preamp
SeleniumFalcon
Posts: 3,781
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!
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Lost me at "input"
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Exciting!
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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:
This screen shot was reduced slightly, not to actual scale. -
Yesterday I received the nuvistor sockets I found on eBay these will be mounted on an external panel.
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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! -
I disabled signatures.
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This is gonna be fun to watch, Ken. Looking forward to progress notes and photos, and, ultimately, performance review.I disabled signatures.
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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. -
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.
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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.
There will be two boards for each channel. The yellow squares are the mounting holes for attaching the boards to the chassis. -
Sweet!
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Olivia has finished the two Gerber files needed to build the PCB and she provided some 3D drawings:
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You, my man, are certifiable! But most geniuses are. Looking forward to following this!Gustard X26 Pro DAC
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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 -
From my recent drivers license:
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I remember the Professor!
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The company that is making the circuit boards has a way to keep track of the process:
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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 along2 Channel in my home attic/bar/man cave
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Nice work! Let us know when your manufacturing company goes public.
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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
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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.
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You're a rare breed Ken!
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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 -
"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 |
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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.
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Ken how long do those super tiny nuvistor tubes last?
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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.
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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.
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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.
