Announcement

Collapse
No announcement yet.

1937 amp head

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • 1937 amp head

    i recently bought on ebay a 30 watts tube amp PA...and i am searching for any information about it. No tubes...no schematic...but i thing it's a challenging restoration project...hhhheeeellllllpppppp fellows!!!
    Attached Files

  • #2
    Google.

    Your photo shows it is an Electroacoustics (division of Magnavox) Model A3023.

    Not sure how you got 1937, but I'll take it. If I had to guess, I;d think at least ten years later, but I don't know.

    The schematic tells what tubes are used. Read the text, a quick scan led me to wonder just what impedance load it wants. I'll look more closely later.
    Attached Files
    Education is what you're left with after you have forgotten what you have learned.

    Comment


    • #3
      enzo you are the man!!! thanks a lot...the only information on internet about the unit: 30-watt Amplifier Amplifier Electro Acoustic Products Co., b

      first year of production was 1936 - 37...mine is coming home in a few days...i was told that maybe the serial in pots or caps can reveal a real age.

      thanks a lot.

      Comment


      • #4
        I am no expert. But I do rebuild old juke box amps from time to time, and the 1938 Rockolas and similar have tubes like the 2A3 and four and five pin tubes with 2-digit type numbers.

        On google, I searched "electroacoustic A3023", and about the third thing down was the swchematic on a web site ENGINE ROOM.....

        I could read the legend on the baqcks of the pots, but couldn;t read a good date. Might be some good numbers on the4 can cap the transformers, even some larger caps.
        Education is what you're left with after you have forgotten what you have learned.

        Comment


        • #5
          Originally posted by fedcarmo View Post
          i recently bought on ebay a 30 watts tube amp PA...and i am searching for any information about it. No tubes...no schematic...but i thing it's a challenging restoration project...hhhheeeellllllpppppp fellows!!!
          considering 6J7 preamp tubes and field coil speaker output...
          makes it right about late 1930's for sure no later than 1942.
          And a really nice amp, I may add.

          Comment


          • #6
            BEWARE that in that schematic, on resistors "M" does not mean "Megohm" but "kiloohm".
            Megohm is indicated by "Meg."
            And in electrolytic caps, "M" means "micro-Farad"
            And agree with Enzo that it probably (at least according to schematic) it only has distribution line outputs (125/250/500 ohms) and not regular speaker ones (4/8/16 ohms).
            But of course, if you want to rig a School or Bus Station PA system, that's the perfect amp.
            You may have a "civilian" model though, with a different output transformer.
            Juan Manuel Fahey

            Comment


            • #7
              THESE THINGS MAKE KILLER GUITAR AMPS. THE 6J7 GRINDS LIKE A CHAINSAW. TOTAL ANNIHILATION.
              However you will need to convert the field coil output or use a field coil speaker.
              Field coil speakers sound much sweeter than modern speakers, but finding a really good one is difficult.
              Last edited by soundguruman; 06-08-2012, 08:11 PM.

              Comment


              • #8
                thanks for the comments and ideas...the main intention was make this unit a guitar amp head...like sounguruman suggested...but i don't really have the skills to do that...i am gonna check for tubes (i search on ebay and 6j7's NOS = $20 each, 6C5 and 5Z3 = $10)

                by the way 6j7's beam tubes or metal tubes? I guess glass ones...but if somebody knows...help!

                field coil speakers...good god i really like this projects...because there is a bunch of things i don't really knew!!! but i am going to research about that!

                Comment


                • #9
                  The 6J7 was manufactured first as a metal tube then as a glass bottle 6J7GT.
                  For Tuse like that you can do well to buy from places like Antique Electronics Supply, 6J7GT - Pentode, Sharp Cut-Off | Antique Electronic Supply LLC.
                  You will see that they currently sell for $7.15.

                  Comment


                  • #10
                    And since you want to make a guitar amp anyway, you could easily repurpose those 6J7 octal sockets for a different tube. A 6SJ7 would be similar, but without the cap on top. Or a 6SL7 dual triode could be interesting. SImple rewires in each case.
                    Education is what you're left with after you have forgotten what you have learned.

                    Comment


                    • #11
                      Funny thing is that the amp as shown has only 500/250/125 ohm speaker outputs and speakers shown below have their own impedance adapter transformers.
                      So far so good, typical of a "line distribution" PA system, with speakers far away from the main amp.
                      Problem is they show field coil speakers, which would make sense if each one had its own little independent Power Supply .... but they run with the same 400V as the rest of the amp.
                      Did they *really* run ***400VDC*** along *long* lines all over the place? Crazy !!!
                      Oh my God!!!
                      Juan Manuel Fahey

                      Comment


                      • #12
                        Like a Hammond B3 sending B+ down the cable to the Leslie/tone cab.
                        Education is what you're left with after you have forgotten what you have learned.

                        Comment

                        Working...
                        X