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Electromuse A55 in dire need of repair

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  • Electromuse A55 in dire need of repair

    I recently purchased an Electromuse A55 chassis, made by Valco, on ebay. I knew it wouldn't work but thought it would be a fun project as it has a 6SJ7, 6V6, 5Y3 lineup just like early Champs. I haven't recapped it yet and it badly needs that but I replaced a few obviously blown caps and resistors, put on a 3 prong cord to replace the cut off one and it actually works, a little.
    I am making up my parts list and a couple of items have me stumped. In previous years, someone else has obviously "fixed" this and I am working without a schematic.
    There are two items below, resistors of some kind I trust, that I have never seen before so I can't determine their values.
    Attached are some pics. The lozenge shaped ones have 6 colours on dots on them, and the long cylindrical one seems to have two colours in bands. Since the layout doesn't really correspond to a Champ, I can't even make educated guesses as to their values.
    Can anyone assist?
    Attached Files

  • #2
    Capacitor code

    The little guys with the dots are capacitors.
    Can't tell on the banded one. Probably a cap.
    My advise to you, would be to sit down & draw the circuit.
    It may take a while & a few iterations, but it will be well worth the effort.
    I would start with an amp layout & then draw the schematic.
    After you are finished the amp will reveal what it was designed to do.
    Then you can tweak & mod.

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    • #3
      Thanks JPB. I have over twenty amps that I have recapped etc but had never seen stuff like this before. Based on your advice, I checked out some sites and indeed those are molded mica caps and the long one is a molded round paper cap. There is even a molded flat paper cap hidden under the mica ones. Now I know how to read the values, I will continue the rebuild. I will take a shot at drawing out a wiring diagram and schematic as well.
      The thing operates at about 1/20th power right now and I am sure the filter cap can is original, so I will replace all the caps before I try anything else.

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      • #4
        Last post for this one. I will start a new thread if I run into trouble. The long one is not a round molded paper cap, it is an old dog-bone resistor. I am ready to go with the filter cap can now, but it looks ordinary.

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        • #5
          Originally posted by Resonator Guy View Post
          Last post for this one. I will start a new thread if I run into trouble. The long one is not a round molded paper cap, it is an old dog-bone resistor. I am ready to go with the filter cap can now, but it looks ordinary.
          If it's down on volume I'd start looking at those resistors for drifted values. They're notorious for that.

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          • #6
            It may be working fine but with the speaker cone seized up. Check with another speaker to make sure. If all else fails, you can reference an early Champ with a 6SJ7 pre-amp.
            http://www.schematicheaven.com/fende..._5c1_schem.pdf

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            • #7
              Thanks guys.
              It isn't a speaker problem as I got only the chassis. I am testing with (I hope) a good speaker. I have ordered the parts I know I need so far and after checking Champ schematics, it is a fair bit different. For instance a four part cap can (4x10uf) rather than 3x10uf for the champ. I ordered a 4x20uf can that might get here before Xmas. After that is in I will check all the resistors and see where it goes.
              It is all fun. I might get frustrated if I was doing this for some one else, but it is just a great hobby.

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              • #8
                Electromuse A55 just waiting for a cabinet now.

                I finally replaced every cap and every resistor in this chassis. I always have to wait a while for parts as I don't want a five or six hour drive to get to an electronics store, so I order just about all my parts from AES, one amp at a time.
                It isn't a terribly loud amp but it sounds really good. I have run it through several speakers and have settled on a Teisco Checkmate 28 speaker cab that I already have. That seems to work well, so I will build a head cab to sit on top.
                With a 5Y3, the 6V6 was only drawing 37.1 ma, but with a 5V4 it is drawing 42.5, so I believe that will be alright, assuming my meter is anywhere near accurate. The big bottles also look pretty cool in it.
                Thanks for all the assistance. On to the next one!
                Attached Files

                Comment


                • #9
                  Hey Reso-Guy,

                  Just wanted to touch base with you on this project of yours. I just picked up a similar amp, although mine is Black, not Red, and mine has a few differences that make me think your may have been modified at some point in time. First, mine uses different output and rectifier tubes.........I have a 6AG7 for an output tube, not a 6V6. Also, mine uses a 5-pin rectifier....and it's a 6 volt filament rectifier. This was missing in my amp when I purchased it....but as it worked out, I had a 6Z4 on the shelf....and it fits in there just fine and the pin-out is correct....so I assume it's the proper tube, or close enough! I also note that you have a replaced transformer! Your up-right Power Transformer is positioned such that you can see from the pictures where the holes are for the original transformer that was set into the chassis. I'm assuming that you have a 5-volt winding for your 5V4 rectifier...and my amp has only the 6 volt filament winding being used on all three tubes. Anyway, I plan to 'convert' my amp to a 6V6 tube...but this will take more than just flopping in a 6V6 as the pin-out for the 6AG7 and the 6V6 are quite different. Also, I'm unsure as to just what the output transformer is designed for......so, I think I'm just going to find another OT some please. I gather from your comments that you weren't too happy with the gain in this amp......but it's been a while now, so I was just wondering if you'd done anything else to it to improve on that situation. If so, please let me know. My name is Top....I just found this thread via google....so maybe you won't even get this. If you do, please send me a note. My regular email address is Wharf_Creek at Hotmail dot com. Please note the underscore between Wharf and Creek!! Guess that's it! Hope to hear back from you, and Thanks!!!

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