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?
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.
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.
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.Originally Posted by Resonator Guy
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
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.
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!
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