Guitar tube-amp from junk hi-fi

posted Jan 20th 2011 12:31pm by
filed under: musical hacks

[Tristan Chambers] picked up an old speaker box some friends acquired at a yard sale. It didn’t have any inputs, and there weren’t any tuning knobs like a radio would have, so it’s a mystery what this was originally used for. [Tristan] traced out the circuit and figured out where he could input audio signals which allowed him to hook up an iPod, but it was mono and not very loud. He ended building his own vacuum tube preamp from a schematic he found on the Internet so that he could use it with an electric guitar. As the video after the break shows, the box not only puts out some pretty good sound but it’s nice and loud too.



21 Responses to Guitar tube-amp from junk hi-fi

  • Paul Potter says:
    January 20, 2011 at 12:38 pm

    That really does rock.

    Reply Report comment
  • Focusrally says:
    January 20, 2011 at 12:43 pm

    My grandma has a speaker similar to that which receives a input from a record player through the houses electrical wiring. That could be what it was used for.

    Reply Report comment
  • Erik Johnson says:
    January 20, 2011 at 12:47 pm

    Comes with its own 60Hz accompaniment!

    also, “…the box not [only] puts out some pretty good sound…”

    Reply Report comment
  • jameth says:
    January 20, 2011 at 1:00 pm

    I can’t tell if you need to invest in a tuner, or lessons.

    Maybe both.

    Reply Report comment
  • Alex says:
    January 20, 2011 at 1:00 pm

    Love the jumper cable patch cord.

    Reply Report comment
  • Drew says:
    January 20, 2011 at 1:04 pm

    he needs to make a tone circuit for it, its clipping pretty bad on the highs

    Reply Report comment
  • The Cageybee says:
    January 20, 2011 at 1:14 pm

    @jameth You read my mind!

    Reply Report comment
  • Justin says:
    January 20, 2011 at 1:31 pm

    @Drew
    Hey man, people pay a lot of money for amps with that sort of dirty overdrive (or effects that’ll emulate it.)

    Reply Report comment
  • Aero says:
    January 20, 2011 at 2:49 pm

    His poor neighbors…

    Reply Report comment
  • Mikey says:
    January 20, 2011 at 2:54 pm

    @Aero — agreed.

    Reply Report comment
  • Oren Beck says:
    January 20, 2011 at 3:14 pm

    @Focusrally: Yes, there are a few “Carrier Current” speaker systems of the era when 12AT7 and 6AL5 tubes were commonplace. IIRC some Rauland produced models were used in commercial installs for executive suite remotes etc.

    But, there’s another type of radio with no user accessible tuning settings. FM “SCA” subcarrier channels were used in some cities for services like book reading to the blind, and a doctor’s office network:

    https://secure.wikimedia.org/wikipedia/en/wiki/Subsidiary_communications_authority

    The “reason” for such a history lesson is to introduce the Hacking utility of a control system used in SCA service. Sub to Barely audible after demod at least- tones activated relays that could “do things” all across a city.

    Traffic Light time range settings/reversible lanes etc or in background music services-raise/lower volume so one store’s commercials got muted in a competing store or raised in volume on speakers of the advertised stores:> Hacking traffic lights was and is a CRIMINALLY bad idea. But? Hacking the audio boost/mute of SCA services was a test of RF Hacker chops indeed! Made a bit easier of course by looking at the Motorola PL reeds more than one such system used.

    Sadly- such gear now is almost all history and winding up as excellent re-assignment materials.

    But knowing the past can explain foibles in re-assignment surgery. shortest explanation= Audio suffered horribly by shoehorning into a SCA subcarrier or carrier current path and oftentimes the amplifier sections tried to expand/equalize that audio in compensation..

    If Tristan has any identifier data at all- I’d love to see it posted. Oh- This is a neat hack of course..

    Reply Report comment
  • echodelta says:
    January 20, 2011 at 3:29 pm

    You should be able to cut out the IF circuit and wire in the preamp, it’s the one with the shield on the socket tween the two IF cans. Already shielded, it and short leads with built in ground will kill hum but not from guitar. This thing must have been a dedicated radio or carrier current campus radio, or big Muzak setup.

    It is transformer operated, I see, thankful design. There may be caps feeding the RF signal in from the power-line, these can be death caps. Find them and kill. It could be transformer coupled though, but even that don’t have a modern safety rating so clip it out. This coupling could be causing hum also.
    What causes aspect ratio fubars on video? I can’t stand to watch such. Please check settings and post a test, adjust if necessary then push good vids. Widescrean sucks, westerns made it, we could have done with out that. 3to4 works best on a subject, either a hot model or a hacked model. Some vids on HaD have been clipped off on the right because of this whole aspect ratio mess. I have a test on echodelta9 channel Youtube, it looks great. Stay tuned for a guitar hack soon to be posted that will set standards.

    Reply Report comment
  • Scott says:
    January 20, 2011 at 3:32 pm

    Man…I was actually getting a late 60′s garage band flashback there for a second. Must have been the righteous 60hz tones.

    Reply Report comment
  • strider_mt2k says:
    January 20, 2011 at 4:20 pm

    That is pretty cool considering.

    Well done sir!

    (but yeah get the hum out-then you WAY good!)

    Reply Report comment
  • mjrippe says:
    January 20, 2011 at 4:49 pm

    Tristan – Did you solder to the pins of your 12AX7??? Send me your address and I’ll mail you a socket!

    Reply Report comment
  • John says:
    January 20, 2011 at 5:24 pm

    He’s ok for a beginner.

    But he ain’t no KK Downing or Glen Tipton

    Reply Report comment
  • qwerty says:
    January 20, 2011 at 7:55 pm

    Wilko Johnson’s sound!

    Reply Report comment
  • NiGe says:
    January 20, 2011 at 8:00 pm

    I recognize this. This was a “wireless” speaker. It would recieve audio over a radio frequency from a device that plugged into the receiver. Then you would put this in another part of your house and plug it in and have a “wireless” system…

    Reply Report comment
  • Tristan Chambers says:
    January 20, 2011 at 9:19 pm

    @echodelta the 60hz hum is from two things: the single coil pickup on the guitar and improper grounding in the guitar circuitry, and more importantly the unsheilded audio cable (read: automotive jumper cables) connecting the guitar to the amplifier. There was an IF stage. I removed the tubes early on in the hacking process, and yes it did improve noise.

    @mjrippe you are a sweet heart. I was totally bumbed when I realized that I didn’t have a socket for the 12ax7. I was hoping to use one from the radio but they had the wrong number of pins. Next time… I might rebuild the circuit because I was getting some internal feedback when I buttoned everything up.

    Reply Report comment
  • seanfalloy says:
    January 21, 2011 at 6:13 pm

    that overdrive is almost perfect for most types of music. Not choppy enough for most metal but would be perfect for alot of early heavy metal or rock.
    Nice work on that sounds great.
    Now time to learn to shred.

    Reply Report comment
  • c3711 says:
    January 21, 2011 at 6:39 pm

    no warning or mention of live chasis designs, isolation transformers or the fact that he’s lucky not to have electrocuted himself

    Reply Report comment

    • Leave a Reply

    XHTML: You can use these tags: <a href="" title="" rel=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <pre> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>

    Hack a Day serves up fresh hacks each day, every day from around the web as well as hacking related news.

    Send us your hacks










         



    Hacks

    Resources