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Thread: my little 54 GA-5 needs rescue

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    my little 54 GA-5 needs rescue

    Hi Friends
    I am trying to repair my little amp.
    It has been really messed up for a long time.
    I took it to several people including someone who is supposed to be a good amp tech with 20 yrs experience.
    He is a friend and did some things right. He replaced all filter caps and probably all other caps as well.
    The amp was not in original condition any way.
    I have taken a slow methodical approach testing every resistor and replacing when way off. I noticed a couple of things that were actually soldered to the wrong pins on the 5Y3 and put it back to match the schematic. I should have noted what it was but I didn't. I don't know if it was a mod but it just looked like a mistake. Im almost finished and I just noticed something else that I am about to change back to original. The 470 ohm, 2 watt resistor connected in parallel with the 20uf 50v cap connects from pin 8 on the 6V6 to ground. The resistor was replaced wit a cement 150 ohm, 7 watt resistor. The cap was also changed very slightly from 20uf 50V to 25uf 25V but I don't think that will affect anything. I am concerned about the resistor though. I have included a schematic.

    I need answers about 2 things:
    1/ What was going on with the resistor change? Was there any wisdom or danger with what was done? Am I right to return the amp to original or should I leave that 7 watt 150 ohm in place?
    2/ Are there any mods that would make this amp more harp friendly?
    I am a novice. I do know how to work safely inside an amp and my soldering skills are good but my understanding of tube circuits (or any electronics) is limited.
    I am studying as I go so I need laymans terms.
    Gratefull for any wisdom
    Thanks
    Harpslinger
    Attached Files Attached Files

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  2. #2
    Old Timer Leo_Gnardo's Avatar
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    1/ I can't see why your amp tech friend went to 150 ohms on that cathode R. Perhaps trying to panel-beat a dead 6V6 into delivering some power? Not the thing to do. I'd go back to the 470R, dont' worry 20 or 22 or 25 uF but I would select a 50V rated cap as the voltage may exceed 25V at times when you're really honking a big signal thru the amp. Also put a little distance between the R and C so the C doesn't get baked by heat from the R. Even if it's as little as 3/8 inch.

    Or his vision is poor & he thought is was a 450 ohm resistor. Seen that sort of thing happen. Imagine a tech who's color blind, and too lazy to reach for his ohm meter. Red looks like brown, and brown looks like brown. Resistors off by a factor of 10, no wonder amps don't work so well.

    2/ I'd leave that circuit stock. It's very Champ-like and that's a good harp tone for many purposes. Youl'll need to mic it up & send thru the PA for a gig any bigger than a very small club. You may want to collect a few more amps for different tone and volume choices. I've seen people use everything from a Champ (South Side Johnny) to a pair of Twin Reverbs (Paul Butterfield) for harp. Many of the small Gibson, Sears Silvertone, Wards Airline, Magnatone, & similar amps are good harp candidates.

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    Don't forget the joker g1's Avatar
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    As far as the 5Y3 wiring, was the amp working before?
    The schematic does not show pin numbers for the 5Y3, how exactly have you wired it up?

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    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

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    Thanks

    Wow that was a quick reply./
    Thanks so much for that.
    Im not sure who changed the resistor in question. It could have been there all along.
    But I will take your advice and change it back and Ill take your advice on the 50 volt also. Much appreciated
    I have some other amps.
    I have a 1955 Gibson 9 model GA-9. I have had for about 20 yrs. I have also owned the ga-5 for about that long.
    I have a 1953 National tremotone model 1224. It was also butchered. Someone decided to change every cap. I have had about a year.
    It sounds ok and Ill get into it at some point. Ill just put it back to stock but with high quality components as close to original as possible.
    I also have a 1962 national twin tone model 1210. completely original. needs very little work.
    I have a 1947 Masco MAp-15. I got for 60 bucks really beat up.
    it has had an extra knob installed probably tone control so I have no idea what is going on in there.
    I also have a 50's Lafayette (2) 6V6 PA amp . I cant find schematics so once agin Ill try to just replace whats needed and see what it is like . Also $60.00 but very clean.
    I got a beat up premier twin 8 around 1959.
    I also have a radio tube amp I bought in my ignorance that I have to sell and an old low watt 1960's garnet that I also have to get rid of and a 1948 Kiesel completely original and clean. Lowell Kiesel was the founder of Carvin amps. It is beautifully made and very nice dark brown alligator tolex with beautiful gold grill cloth. Beautifull soldering job with red laquer to seal all the joints.
    The cabinet has an outside dimension of 13 1/2 inches and a 12 in speaker inside. crazy. I don't think it will be good for harp though and I don't want to touch it. Id rather pass it on to someone ( probably a guitar player) who would value it as is and make their own restoration. Ok Im probably boring you to tears now.

    The only way I could afford to buy all this gear is to feed my children every second day.

    Thanks again for your help Leo
    Harpslinger








    Quote Originally Posted by Leo_Gnardo View Post
    1/ I can't see why your amp tech friend went to 150 ohms on that cathode R. Perhaps trying to panel-beat a dead 6V6 into delivering some power? Not the thing to do. I'd go back to the 470R, dont' worry 20 or 22 or 25 uF but I would select a 50V rated cap as the voltage may exceed 25V at times when you're really honking a big signal thru the amp. Also put a little distance between the R and C so the C doesn't get baked by heat from the R. Even if it's as little as 3/8 inch.

    Or his vision is poor & he thought is was a 450 ohm resistor. Seen that sort of thing happen. Imagine a tech who's color blind, and too lazy to reach for his ohm meter. Red looks like brown, and brown looks like brown. Resistors off by a factor of 10, no wonder amps don't work so well.

    2/ I'd leave that circuit stock. It's very Champ-like and that's a good harp tone for many purposes. Youl'll need to mic it up & send thru the PA for a gig any bigger than a very small club. You may want to collect a few more amps for different tone and volume choices. I've seen people use everything from a Champ (South Side Johnny) to a pair of Twin Reverbs (Paul Butterfield) for harp. Many of the small Gibson, Sears Silvertone, Wards Airline, Magnatone, & similar amps are good harp candidates.

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  5. #5
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    Hey g-one
    Thank you. Man this forum is awesome I cant believe how quick I hear from people.
    Sorry here is another schematic with pin #s
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  6. #6
    Don't forget the joker g1's Avatar
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    Well, if you have wired it that way it is correct. Was it working with the alternate wiring before? It's possible they were just using some unused socket lugs as tie-points.

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    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

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    Lifetime Member Enzo's Avatar
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    So after all this discussion, just WHAT is wrong with it that you are trying to fix?

    it may have different resistor values than we expect, but what does it do wrong?

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    Im gonna double check to make sure it is according to the schematic.
    Im a little insecure because the schematic does not tell me what colour coming from the transformer goes where.
    So Im going by the other connections the wire makes to identify it.
    I will not turn it on until I am more certain of what is going on.
    Thanks again
    Ill keep you posted.

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    I wired it correctly,
    I do not know if a lug was used just to join the wires from pin 8 but there are 8 pins on the 6SJ7.
    None of the lugs would be empty.
    Im not sure what the 8 pins do so maybe one or more are not being used and would not be affected but I feel safer this way.

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  10. #10
    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by harpslinger View Post
    Im not sure who changed the resistor in question. It could have been there all along.
    Wow, you have a harp amp museum! Just gotta get some of 'em working better. The Kiesel sounds a treat - back when Carvin had good amps. Let's get your GA-5 gem going then the rest one by one. Twin-8 another fantastic harp amp. I'm knocked out.

    The circuit for you GA-5 output is so similar to a Champ I'll bet 470R is the right value. You can do a little detective work by looking at solder connections & neatness of build. New looking solder, sloppy work, it's been repaired. Proper amount of corrosion and dust on the solder & part squared away nicely in the chassis, likely original build.

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    Hey Enzo,
    It was originally making a harsh kind of loud screaming/gargling noise.
    If I slapped it the noise would go away, Eventually it would not go away.
    One guy put in a new tube, (a metal 6V6 which I got rid of immediately) but to no avail.
    Another did something else, I have no idea what. Still no good.
    Then the amp tech did get it fixed but I lost my tone, it sound muffled and and it has a very loud hum.
    I believe the hum increased as the volume was turned up.
    Which he seems to want to ignore. But the hum is very loud.
    The amp does have a 3 prong plug by the way.
    I have inspected every solder joint and some had way too much and some too little so I sucked a lot of old solder out and put new.
    I cleaned tube socket pin holders, input jacks and the volume pot.
    I picked up some carbon film resistors locally today to get it going again.
    I should be done tomorrow.
    When I do get it working properly I will replace with carbon comps.
    I will never sell this amp as it was given to me by my son about 20 yrs ago so I hope I can get it back to where it was.
    I have played through a champ and I like this better.
    The champ was more powerful but harsher and would feedback very quickly. Im sure it could be modded. But The Gibsons distortion is warmer and creamier.

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    all done, here is a photo

    Thank you to Leo and g-0ne and Enzo.
    I finished working on the little Gibson today.
    I plugged it in and held my breath. It was absolutely quiet, awesome I thought.
    I let it heat up then turned the volume up full still no hum or noise at all then I plugged in my mic and turned it up and still no sound.
    What a bummer. I was totally discouraged. I changed tubes still no good. Oh man I thought maybe I fried something with too hot soldering iron and no heat sink.
    I went to my office praying all the time for God to help me and show me what was wrong.
    I sat in my chair in the office and it crossed my mind that it could be as simple as a wire on the volume pot being soldered wrong or something simple not necessarily a big problem
    I went back to my bench and opened it up. (drained the caps) and as I was looking around guess what I saw. One of the wires from the volume pot to the power tube was disconnected... I had earlier taken that wire off to get at something else and said to myself I have to remember to put that back on. But I forgot to.
    I soldered it, put it back togeather, turned it on and held my breath. Wahoo!. It sounds great. No more grizzly noise and no hum at all. Well a barely audible hum that does not increase with the volume control. It is completely playable for the first time in about 10 years.
    Even My tech didn't know what was up with the loud hum.
    I found some wires from the power Transformer that were soldered to the wrong pin on the rectifier tube so I changed it to match the schematic and I think that was the problem.
    No problem now
    Ive included a photo
    Thank you all very much for the encouragement and technical advice.
    Now on to the next amp
    By the way my son plays guitar and he is purchasing a national glenwood amp.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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