Announcement

Collapse
No announcement yet.

Melody A-3LNP (Teisco #61?)

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

  • Melody A-3LNP (Teisco #61?)

    Looking for a schematic for this little tube amp. The circuit board says A-3LNP. It has 4 tubes: two 12AV6, one 50C5, one 35W4. Don't know if those are the tubes that are supposed to be in it, just what I got it with. Two knobs, tone and volume. One 8" three watt 8 ohm speaker. No PT, only OT. I'm sure this is a typical cookie cutter circuit but it would be nice to have a schematic it it exists.

    Pretty much looks like this one. https://reverb.com/item/2773706-vint...-made-in-japan

    Thanks,
    Greg
    Last edited by glebert; 10-17-2017, 07:28 AM.

  • #2
    I see that there was an AA5 variation that used 12AV6, 50C5, and 35W4 so this is probably very similar with an extra 12V6 gain stage?
    Last edited by glebert; 10-17-2017, 05:37 AM.

    Comment


    • #3
      In case anyone else is looking for this schematic the AA4 design done by Joe Bento (based on a design book by Tino Zottola) is pretty close in structure with some different component values. If the link dies do a search for AA4 schematic. I love that he build his prototype with a bread pan as a chassis.

      AA4 prototype and schematic
      Last edited by glebert; 10-20-2017, 05:29 AM.

      Comment


      • #4
        Cool, but if it´s still
        No PT, only OT.
        then you MUST add an isolation transformer, as in the bread pan chassis one you show.
        There´s lots of threads here on that very subject.

        Post a couple pictures, both inside and external
        Juan Manuel Fahey

        Comment


        • #5
          Originally posted by J M Fahey View Post
          Cool, but if it´s still then you MUST add an isolation transformer, as in the bread pan chassis one you show.
          There´s lots of threads here on that very subject.

          Post a couple pictures, both inside and external
          Agreed on the isolation transformer. This amp is not hot chassis, there is a resistor and cap between chassis and circuit ground, but isolation transformer is necessary.

          I will post some pics, but this amp has not been babied. I had to give it a gentle scrub down with isopropyl alcohol just so my DMM probes could get through the 60 years of grime on the traces and solder joints.

          Comment


          • #6
            Thread revival, just because I finally found a schematic for this amp. Someone is selling one on Ebay and was nice enough to put a pic of the schematic in the sale.

            Click image for larger version

Name:	Melody_A3L_schematic.jpg
Views:	1
Size:	264.8 KB
ID:	851622

            Comment


            • #7
              Click image for larger version

Name:	Melody_A3L_schematic.jpg
Views:	1
Size:	162.7 KB
ID:	851629
              "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

              Comment


              • #8
                Thanks for the cleanup!

                Comment


                • #9
                  Reminder

                  Input tube (1st 12AV6) no cathode resistance (cathode on ground), resistance in g1 should have a value of 10 Mohm
                  It's All Over Now

                  Comment


                  • #10
                    Originally posted by vintagekiki View Post
                    Reminder

                    Input tube (1st 12AV6) no cathode resistance (cathode on ground), resistance in g1 should have a value of 10 Mohm
                    The schematic says 1M (kind of faint, looks like a schematic edit), but that should be 10M? I suck at tube theory, can you explain what difference that will make? I can check and see what is actually present on my amp.

                    Comment


                    • #11
                      Grid-Leak Biasing

                      https://www.diyaudio.com/forums/tubes-valves/272689-grid-leak-bias.html
                      Grid leak bias, how does it work?

                      http://sound.whsites.net/valves/bias-gain.html#s31
                      Grid Leak Biasing

                      http://electriciantraining.tpub.com/14178/css/Grid-Leak-Biasing-45.htm
                      About Grid-Leak Biasing see Page Navigation (up, right) page 33 - 36

                      http://www.valvewizard.co.uk/Common_Gain_Stage.pdf
                      Common-Cathode, Triode Gain Stage

                      https://ampgarage.com/forum/viewtopic.php?t=29704
                      Further Grid Leak Bias Questions

                      https://music-electronics-forum.com/showthread.php?t=32789
                      Why was grid-leak/contact bias used in guitar amps?

                      https://music-electronics-forum.com/showthread.php?t=30471
                      Grid leak bias and hum...

                      https://music-electronics-forum.com/showthread.php?t=22484
                      Grid leak/contact bias preamp

                      http://www.valvewizard.co.uk/Common_Gain_Stage.pdf
                      Triode Gain Stage

                      Some guitar amps with Grid Leak Bias

                      http://www.magnatoneamps.com/schematics/magnatone_M-197-3-V_PM.pdf

                      http://www.magnatoneamps.com/schematics/magnatone_M-195-4-J-1949.jpg
                      It's All Over Now

                      Comment


                      • #12
                        Ah, my confusion was that I misread the schematic as the 1M as being between cathode and ground (with no resistor symbol) but that 1M is actually the value of the grid resistor and is superimposed over the cathode net.

                        Comment


                        • #13
                          https://www.tremolo.pl/Firmowe/TeiscoJapan/Teisco_Tube_Amp_Model_62.jpg
                          Teisco Tube Amp Model 62
                          It's All Over Now

                          Comment


                          • #14
                            Originally posted by vintagekiki View Post
                            Thanks!

                            So in addition to getting this working I will need to convert it from grid leak biased to cathode biased. I did get it partially functional, but it buzzed like a kazoo. I assumed that was because my voltages were low due to old caps and crappy connections, but maybe it was distortion due to the grid lead biasing. And low voltages.

                            Comment


                            • #15
                              Originally posted by glebert View Post
                              So in addition to getting this working I will need to convert it from grid leak biased to cathode biased.
                              If you want to experiment, you can easily custom that the input tube is working in grid-leak or cathode bias mode.

                              https://i.imgur.com/SRjx8qO.gif
                              Grid-leak or cathode bias
                              It's All Over Now

                              Comment

                              Working...
                              X