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1963 Gibson GA-5T Skylark

Discussion in 'Amp Tech Center' started by Omni7, Aug 14, 2017.

  1. Omni7

    Omni7 TDPRI Member

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    Hello Im new to the forum so forgive me if this has come up before.
    I am working on a 1963 Gibson GA-5T Skylark and trying to get the most out of it.
    I have replaced the original speaker with a 10inch alinco speaker, got rid of the death cap, stuck a three proged cord on it, replaced all the caps, changed the on/off swich (It was faulty) and finally changed all the tubes for Nos. I would love to know if there are any other mods out there?

    Here are some things i would love to do -

    1) I would dearly like to tame the Tremolo a bit by getting a little more direct guitar signal with it, rather than the tremolo sounding all effect.

    2) I like to get the impression of a little more Sag, the circuit is quite unforgiving!

    3) I would like the breakup to be a little less harsh. (ironically it has only been harsh since I changed the big cap to 3 new spragues. (I am thinking of putting the old large cap back in because after I took it out I measuring its ESR and was shocked to find it was better than any new caps I had ever tested and this thing is old!

    Anyway.. Many thanks in advance for any help advice and tips you can give me with this lovely little amp!
     
  2. zook

    zook Friend of Leo's

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    What is the tube complement of your amp? There are several different versions of the GA5T.
     
  3. Omni7

    Omni7 TDPRI Member

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    • Hi, Zook its got the following specs
    • 1x10"
    • 5 watts
    • 1 6X4
    • 2 6AQ5 power tubes
    • 2 6EU7 preamp tubes
     
  4. zook

    zook Friend of Leo's

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    There is no Depth control on your amp for Tremolo. If you look at the Schematic you will see a 330K resistor to ground at the junction of the two 220K resistors in the Power amp section. Replace that with a 250KL or 500KL pot (depending on your ear, ) and you should have an intensity control. If that doesn't work, look at the GA16T (GA18T) schematic and reconfigure the tremolo circuit to that one.
     
  5. Crashbelt

    Crashbelt Tele-Holic

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    I'm no tube amp expert but I'd confirm the the tremolo circuit on my GA18t is really sweet and very musical sounding so great if you can replicate that as soon suggests.
     
  6. Omni7

    Omni7 TDPRI Member

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    Many thanks thats great!
     
  7. Omni7

    Omni7 TDPRI Member

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    (This trems really sweet too i'm just being a tad fussy and would love about 15% more direct guitar signal mixed in) Thanks for your reply
     
  8. muscmp

    muscmp Tele-Afflicted

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    i have the ga5t with the same configuration. i've swapped the speaker for a weber. since it is no depth control, i either tweak the knob or run without tremolo and add a pedal in front to use it as a recording amp. great sound either way.

    play music!
     
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  9. Milspec

    Milspec Poster Extraordinaire

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    I have a White Panel using 2x6BQ5 tubes, but yours must be the Crestline if it has the 2x6AQ5. I don't know what the circuit changes are (there were many changes over those years), but mine doesn't have a harsh break-up at all and yours should be even better.

    I did install the smooth cone WGS speaker which made a world of difference in taming the treble on that thing. Maybe that is why it doesn't get harsh when pushed either?

    Cool little amps and seem built quite well, but I guess I am not much help to you.
     
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  10. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    don't do it!

    Old caps are past their service life and can fail without warning. it makes no difference how it tests or how the amp sounds with it - they have a service life of appx 15 years and beyond that you are on borrowed time. You can have a failure without warning that can take out your power transformer. It's not worth it.
     
  11. Omni7

    Omni7 TDPRI Member

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  12. Omni7

    Omni7 TDPRI Member

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    Yes Silverface this is the reason I replaced them all because I had read they could go bad at anytime. It's just a pity the breakup is a little harsher. Still there are two other components that are not reading well lets see how it goes after these changes.!
     
  13. Omni7

    Omni7 TDPRI Member

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    Always great to here about the potential of amps! what was the name of the speaker you used?
     
  14. Milspec

    Milspec Poster Extraordinaire

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  15. dkevin

    dkevin Tele-Meister

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    Have you attempted to check the layout against the published schematic? I have owned several of these amps. There are a few things that can be addressed besides the speaker. I found and removed the Sprague network in the preamp. I replaced it with a .02 cap. Then, I found the cathode bypass cap for V1b to be .1uf which emphasized the harsh treble content and minimized the bass response. This cap is not found on the 5T schematic and yet, there it was is real life! There is great benefit in making a hand-drawn layout and comparing the components you see with the ones supposedly installed by the factory.
     
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  16. Omni7

    Omni7 TDPRI Member

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  17. Omni7

    Omni7 TDPRI Member

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    I am really struggling my way through the amp having no previous experience of electronics at all so im just picking up ittle things very slowly. Im certainly no good enough at this moment to br reading the schematics very well. I have simply watched some videos and read things on net, improved my soldering and taking a learning curve to get this amp the best i can. Thanks for your input!
     
  18. muscmp

    muscmp Tele-Afflicted

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    the reason dkevin states this is that gibson was known for not following their own schematics.

    play music!
     
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  19. Omni7

    Omni7 TDPRI Member

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    Good job i am replacing like with like instead of following their schematic then! :)
     
  20. Tele wacker

    Tele wacker Tele-Holic

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    Did you try the amp with the tubes that were in the amp? Did you test the tubes?
    After changing all that stuff, you may have a really different sounding amp from the original amp.
    I will change some components but never do I go in and change everything without some testing and listening first.
     
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