Frankenstein, an all-tube home theater amplifier

amp

Here’s an exercise in excess if we’ve ever seen one. While working on his undergrad at Michigan State, [Gregory] thought it would be a great idea to build an all-tube home theater system. He calls his seven-foot tall rack of amplifiers ‘Frankenstein,’ and we’ve got to agree this build is an impressive monstrosity of engineering prowess.

[Gregory]‘s Frankenstein is a complete 5.1 home theater system. In the interests of sanity, the majority of the equipment in the rack is off-the-shelf gear including a CD player, surround sound processor, and a beautiful McIntosh solid state preamp. The power amps, though, are where this build really shines.

For the sub, [Gregory] built a wonderful monoblock tube amp, able to push nearly 300 watts into a subwoofer. The other channels for this home theater system are amplified with a huge four channel tube amp providing 480 watts per channel. In total, there are 23 tubes in [Gregory]‘s amplifier system, enough to consume 20 amps of filament current.

You can check out [Gregory]‘s demo video of his system after the break.

Comments

  1. Repost(again, this is like the 3rd or 4th time I see this here).

  2. Cold_Turkey says:

    ^^^ most pointless comment of the year! Why do peole who have nothing nice to say still bothet? I have been reading hackaday for many years and I have never seen this anywhere before let alone on here! Great build! Who wouldn’t love one of these?!?

    • metro says:

      I agree. Not a post I have seen anywhere before, let alone here.
      Sticking to the point its a well documented and interesting build. Can someone explain how he is getting almost 300w output at low THD from a pair of EL34’s; which should have a Max of around 50w.

      • Nico Verduin says:

        Based on the 550V (or something like that) he is using on the Penthodes he might theoretically push spikes to that output power. But it would be more interesting to calculate and measure the real output power. I suspect somewhere between 50-60Watts. But you would need the primary impedance of the outptu transformer to calculate that. But for a living room still high enough. Nice design. Don’t see menay do this anymore unfortunately. Most buiders just copy design and fiddle a bit with components

        • Nico Verduin says:

          Just checked his Output transformer he used. It is a Hammond 1650 Ultra lineair OT primary impedance of 6K6 ohm and max power output of 40W. Max current 200mA. If he were to push it a lot more, the primary coil would melt en short circuit. Due to the UL type OT and high voltage, he is probably getting something like 50-60 watts.

  3. mental2k says:

    Awesome, those switches have a very satisfying thunk to them as well. Probably don’t need the heating on in the room either!

  4. Bertho says:

    Although I like the setup, I still have to think about the power usage of this rig. It must cost a fortune to keep it running.

    Ah well, when you can afford to build it, you may have the wallet to feed it too, I guess. ;-)

  5. Natalie says:

    Awesome build.
    Did anyone figure out if he measured THD and other parameters under operation? .65 % THD for a tube amp typically achievable at less than 1 W.

    PS has anyone tried a smart biasing network with protection on the output tubes, there is significant amount of money tied up there in glass?

  6. laazarus says:

    at the end of the power up sequence did any one else half expect the camera to pan back to show Marty McFly standing in front of a massive speaker with a guitar?

    just a shame there’s no way of knowing how it sounds with out been there,

  7. mjrippe says:

    Those peak power ratings are a bit misleading. According to the RCA Receiving Tube Manual (RC-30), EL34 in class AB have a maximum signal power output of 40 watts each.

    • whatsthis says:

      “A bit” ? He claims 480 Watts per channel and he’s using two 25W tubes in AB … that’s only 10 times more than what those tubes are capable of delivering …

      I’m surprised to read all the appreciative comments here. It looks like a big heap of garbage to me. Bad amps and bad signal switching.

      • SleeperService says:

        i agree. this is a fairly easy to make setup and overdriving the valves like he is makes it even worse for audio than transistors!
        and why use the mac SS if hes gone to all the trouble of making the valve amps…
        all in all not a very impressive build.

      • Rob says:

        maybe it’s a PMPO vs a RMS measurement? Remember when all the computer speaker manufacturers started bragging with PMPO numbers back in the late 90’s? Took folks a few years to get that sorted through. The 10:1 ratio here seems like a similar thing. I could be all wrong, but that’s the only explanation I can come up with.

        • Rob says:

          In re-reviewing his write-up on the four channel amp, he’s claiming 80w per channel, RMS. In the write-up of the monoblock, he’s claiming 50wpc, RMS, and that there are five monoblocks for the system. So if all 6 units (nine channels total) are in play, that’s a max total of 570 watts, RMS.

          In short, no matter how you count the amps or run the maths, you still end up with different watt totals from article to article. I wish the creator would chime in and explain how he’s getting the wattage he claims and how he gets his totals. Would really help clarify things.

        • Rob says:

          SOLVED! As I suspected, he is measuring Peak Power Output (which does matter, it’s not strictly a method to generate big numbers). See his whitepaper on the whole project here: http://web.mit.edu/gr20603/www/website%20pdfs/MIT_Haystack_Lunch_Talk_2_3_10.pdf

  8. Whatnot says:

    There is a flaw, it’s not completely cat proof.

  9. Rick Autry says:

    As an added bonus, you never have to pay home heating bills again! Summertime, it’s perfect for driving a heat pump, or just add a couple ‘o hundred pelletier junction units to keep a bunch of deep cycle cells charged and ready for led house lighting, or the odd power failure, all in the name of even order harmonic goodness! May the great goddess Mho smile upon that gorgeous temple you have built for her!

  10. h_2_o says:

    I don’t say this often but that is beautiful, as a tube fan i can only imagine the sound

  11. echodelta says:

    Tube goodness whoa! Lust! But do gunshots sound as good?
    I stopped the video when the faint mumbling of a description started. I don’t turn my audio system up when it’s on the computer, it’s set for full broadcast quality audio level and delivers. Card mixer allows radio in, and file and web activity.
    Please don’t talk near or around a camcorder or phone. Talk right into it in front less than 4 feet away. Since there is no post production on this type video, it goes straight to the web.

  12. mixadj says:

    Great project. I might have my priorities wrong but I was more impressed by his solution for the record player…. I might have to hide my Technics turntable like that now. I need to start looking into tube audio amps and see what all the fuss is about. I might go find that tube headphone amp that’s floating around on the inter-webs. I have used tube HF radios but never anything for Hi-Fi.

  13. Hedley says:

    awesome. I would love to see the waf on that system, “honey, first the switch on the right, then wait… then the left switch… ” ;)

  14. thefekete says:

    Think you meant “Frankenstein, an all-tube home heater / amplifier”

  15. Mike says:

    How much did those tubes cost? Last I checked the cheapest tubes in my area were around $80 a pop.

  16. mark rehorst says:

    I’m sorry to be contrary, but tubes suck. Every minute this thing is on the tubes and sound are degrading. Cost of replacing them is going to be astronomical, especially at the prices that tube audiophools have created in the last 10 years or so. I know, I know, I’ve heard all the crap about even-order harmonics and euphonic distortion, but I prefer no audible distortion which can only be achieved with solid state amps operated well within operating specs. And vinyl! Don’t get me started on vinyl…

  17. mrz80 says:

    Ok, a pair of EL34s running AB? Just the thing for a guitar amp, but in a high fidelity application? Thanks but no thanks. I don’t want my amplification adding “character” to the output – you’ve by definition drifted from *reproduction* to *production*. Naughty naughty. :)

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