Odd 1 Watt Amp

Discussion in 'Project Depot' started by Manodano, Apr 17, 2019.

  1. Manodano

    Manodano Well-Known Member Supporting Member

    Joined:
    Jan 25, 2015
    Messages:
    2,182
    Likes Received:
    3,552
    Trophy Points:
    113
    Location:
    Nashville
    I came across this simple circuit on pintrest for a 1 watt amp using a 12ax7 with an automobile ignition coil as an output transformer. Interesting, but the coil does not isolate plate voltage from speaker output.

    Unless this is just too risky to experiment with, I think with some mods it might be interesting to. experiment with in order to build a flea powered bedroom amp.

    https://www.allaboutcircuits.com/textbook/experiments/chpt-5/vacuum-tube-audio-amplifier/

    Comments?
     
  2. Manodano

    Manodano Well-Known Member Supporting Member

    Joined:
    Jan 25, 2015
    Messages:
    2,182
    Likes Received:
    3,552
    Trophy Points:
    113
    Location:
    Nashville
  3. toomanycats

    toomanycats Well-Known Member

    Joined:
    Dec 29, 2014
    Messages:
    7,679
    Likes Received:
    17,271
    Trophy Points:
    113
    Location:
    North Carolina
    I know just enough about this stuff to probably electrocute myself. I'm really hoping you build one though.
     
    Jaymo and Partscaster like this.

  4. andrewsrea

    andrewsrea Well-Known Member

    Joined:
    Jan 1, 2009
    Messages:
    7,633
    Likes Received:
    6,333
    Trophy Points:
    113
    Location:
    Lake St. Louis, MO
    Operates on the same principles of car radios which operated on vacuum tubes, which were highly isolated components.

    Unless you are experimenting , I'd pass.
     
  5. Mickey

    Mickey Gandalf the Intonationer

    Joined:
    Jun 8, 2007
    Messages:
    33,071
    Likes Received:
    20,290
    Trophy Points:
    113
    Location:
    Wausau, Florida
    IF I built it I'd put a cap in series with the + speaker lead to make sure ONLY AC goes to the speaker.
     
    Manodano and andrewsrea like this.
  6. Poodlesrule

    Poodlesrule Well-Known Member

    Joined:
    Aug 12, 2008
    Messages:
    5,331
    Likes Received:
    3,221
    Trophy Points:
    113
    Location:
    East of Eastern MA
    Hijack: there were vac. tubes in olden car radios..?

    Other: For some reason this reminds me of Occupy Boston, where a few odd human power electricity generation units were set up!
     
  7. Mickey

    Mickey Gandalf the Intonationer

    Joined:
    Jun 8, 2007
    Messages:
    33,071
    Likes Received:
    20,290
    Trophy Points:
    113
    Location:
    Wausau, Florida
    It wasn't until the 1960's that you had transistorized car radios.
    Also, until the 1960's there were only AM radios......not AM/FM.
     
  8. mozz

    mozz Well-Known Member Supporting Member

    Joined:
    Jun 10, 2015
    Messages:
    2,121
    Likes Received:
    2,834
    Trophy Points:
    113
    Location:
    NEPA USA
    High voltage on the speaker? Pass. It's a triode anyway, you want a pentode for a output tube. Never heard anyone who liked triode mode. Almost any tube desktop radio or clock radio with tubes will have a decent small single ended output transformer for a project.
     
    Manodano and Mickey like this.
  9. toopicky

    toopicky Well-Known Member

    Joined:
    Sep 23, 2010
    Messages:
    408
    Likes Received:
    385
    Trophy Points:
    63
    Location:
    Malfunction Junction
    Yep. The good old days. Seems like I was always replacing those vibrators or what ever they were called in those tube radios.
     
    Mickey likes this.
  10. Mickey

    Mickey Gandalf the Intonationer

    Joined:
    Jun 8, 2007
    Messages:
    33,071
    Likes Received:
    20,290
    Trophy Points:
    113
    Location:
    Wausau, Florida
    Yep, my uncle made a ton of money (for the day) replacing vibrators in car radios back in the day. :)
    For those who only know "Vibrators" as a female sex toy, they were an electromechanical device
    used to convert DC to AC so it could be stepped up with a transformer so it could be turned into
    high voltage DC needed by tubes. :)
     
  11. andrewsrea

    andrewsrea Well-Known Member

    Joined:
    Jan 1, 2009
    Messages:
    7,633
    Likes Received:
    6,333
    Trophy Points:
    113
    Location:
    Lake St. Louis, MO
    That is where the 6V and 12V heater requirements came from. 6V from European car batteries and early American ones, and 12V from American car batteries.

    For a 12AX7, the '12' is heater voltage and most likely evolved from some type of 12v American transportation system (car , plane, etc.) . 6EU7, the '6' is a 6 volt heater and probably evolved from European requirements.

    Simple car radio designs only used a tube or two and had a watt or less output. Some of the ones @Mickey and @toopicky are talking with a vibrator, were the HiFis and had 5 watt systems (ooh!). Great Grandpa didn't have a trunk full of sub-woolfers, for sure.
     
    jimytheassassin and Mickey like this.
  12. Mickey

    Mickey Gandalf the Intonationer

    Joined:
    Jun 8, 2007
    Messages:
    33,071
    Likes Received:
    20,290
    Trophy Points:
    113
    Location:
    Wausau, Florida
    Yep, the changing auto electrical systems is what caused a lot of later tubes to have a center tapped filament (for example 12A?7, can be used in either 6 or 12V autos.)
     
    andrewsrea likes this.
  13. Jaymo

    Jaymo Well-Known Member

    Joined:
    Jun 17, 2017
    Messages:
    847
    Likes Received:
    722
    Trophy Points:
    93
    Location:
    Georgia
    I'm going to build one in the hopes that I DO electrocute myself. :D
     
    toomanycats and Mickey like this.
  14. Zipslack

    Zipslack Well-Known Member

    Joined:
    May 21, 2015
    Messages:
    628
    Likes Received:
    615
    Trophy Points:
    93
    Location:
    Wesson, MS
    If you're lucky, you can find old vibrator radios with 12ax7 and 6v6....a Champ waiting to happen!
     
  15. Poodlesrule

    Poodlesrule Well-Known Member

    Joined:
    Aug 12, 2008
    Messages:
    5,331
    Likes Received:
    3,221
    Trophy Points:
    113
    Location:
    East of Eastern MA
    This reminds me, I have a Zenith tube tabletop radio in working condition. Need to open the thing to see what's in there.

    Oh, and a 1920's RCA (with schematic!) which I fired up four years ago - without taking precautions, because I did not know any better then. Old caps taking the whole thing down and such.
     
  16. Manodano

    Manodano Well-Known Member Supporting Member

    Joined:
    Jan 25, 2015
    Messages:
    2,182
    Likes Received:
    3,552
    Trophy Points:
    113
    Location:
    Nashville
    Thanks for the comments, nobody seems too excited about the oddball circuit, including me. Sometime people post things on the internet that are actually crap. Present company excluded, of course.

    I'm pretty sure that the rich sound coming from the Delco AM radio in my Dad's 1956 Olds Rocket 88 is what hooked me on music at a very early age. I remember thinking that the transistor radio in his 1965 Impala sounded like crap.
     
    jimytheassassin likes this.

Share This Page