Here is something you never hear about

Discussion in 'Ampage Area' started by noelweller, Dec 12, 2008.

  1. noelweller

    noelweller Banned

    Age:
    46
    Jun 25, 2008
    schaumburg
    With all the talk of small tube amps, Fender champ 600, and the Gretsch 5222. The one amp I never hear about is the Gibson GA-5 Les Paul.
    ANd a big plus for everyone, it's point to point wired.
     

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  2. mugsy

    mugsy Synchromatic

    766
    Nov 3, 2008
    Indiana
    Those are great little amps. I have a pair--one stock and one undergoing some changes. Some cool features: made in the US, Heyboer transformers, JJ/Tesla tubes, el84 output tube, Sprague/Mallory caps, turret board construction, and they usually go for around $300. It's a very loud 5/6 watt amp--much louder than the G5222.
     
  3. Bonedaddy

    Bonedaddy Banned

    Jun 8, 2008
    Silicon Valley
    I've played one, for the money, I'd look around for a Silver Faced Champ.
     
  4. roadjunkie

    roadjunkie Country Gent

    Jul 4, 2008
    Middletown,PA
    I had one. It was a nice lil' amp but wasn't on par tone wise with the TH Prince Royale I had. My only real complaint about it was the RCA plug for the speaker. I would play the TH thru a Blue and it was near nirvana! I couldn't do that with the Gibby. I miss them both but not as bad these days since I'm covered in the low power tube amp dept. with the Fargen and Allen.
     
  5. mugsy

    mugsy Synchromatic

    766
    Nov 3, 2008
    Indiana
    I wasn't keen on the RCA output either, so it was changed to a standard 1/4". I also added a SPDT switch to take advantage of the 8 ohm tap that taped up next the OT. Now I just need an extension cabinet :)
     
  6. unbridled

    unbridled Synchromatic

    926
    Aug 20, 2008
    Montana
    Here's Mine

    Even though they look similar, there are actually differences in the GA-5s. Mine is an 03 model and is different from the ones like Mugsy had. (I'm assuming) The most noticable differences between models like mine and others are the lack of a protective screen on the back of the amp and behind the grill cloth. There is also no cord box like those found on the later models that you are supposed to try to shove the power cord in for storage. The big difference, however, is in the electronics. Models like mine use Sprague caps (I can't remember what the others use) The OT is also different on models like mine and doesn't have an 8 ohm tap like the others. Another thing that is kind of wierd is that no where at all on either the amp, or the packaging (I still have it, although the amp is an '03, I've only had it about 6 months. It was new, old stock) that refers to it as a GA-5. It simply calls it a G-5.

    Maybe I got lucky or have a freak, but I love mine! It's a lot warmer than it should be with only an 8" speaker.

    l[​IMG]
     
  7. JohnnyCrash

    JohnnyCrash Gretschie

    336
    Nov 22, 2008
    Fullerton, CA
    I built a GA-5 circuit for a small practice amp. I put a 10" in it (AlNiCo Jensen P10R). I also added a diode clipping switch for really quiet overdrive stuff.

    With diodes off and running it stock, it's just as good as any Champ, but my favorite 5w circuit has been Kalamazoo Model-One amps. Low plate voltages make for warm overdrive at quieter volumes.
     
  8. ruger9

    ruger9 Country Gent

    Nov 1, 2008
    NJ
    Still looking forward to hearing one of YOUR Kalamazoo-inspired creations, Johnny!
     
  9. mugsy

    mugsy Synchromatic

    766
    Nov 3, 2008
    Indiana
    Hey, that's a cool idea. I'll have to add bits to my next mouser order :)
     
  10. JohnnyCrash

    JohnnyCrash Gretschie

    336
    Nov 22, 2008
    Fullerton, CA


    I can walk you through a diode clipping install if you need help. I added a 3way switch to my Kalamazoo Model One clone I built. Symetrical clipping--Center Off--Asymetrical clipping.

    Also a more "natural" way to get more overdrive out of this thing is to add a cathode bypass cap to the second triode of your preamp tube.

    As you can see from this schematic, the reissues only run one triode with a bypass:
    http://www.diycustomamps.com/pdf/GA5_schem.pdf

    Better yet, add a switch to pull that 25uF cathode bypass on the preamp tube in or out too. Smaller valued caps in the preamp's cathode bypass will overdrive at higher frequencies making for a brighter tone.

    I've built so many 5 watt circuits and tweaked them every way imagineable... they're very simple and extremely fun.
     
  11. Jukebox

    Jukebox Gretschified

    Age:
    64
    Jun 2, 2008
    Foreston,MN
    Johnny did you ever come up with an idea for that little amp that I have ! 1/2 watt?
     
  12. JohnnyCrash

    JohnnyCrash Gretschie

    336
    Nov 22, 2008
    Fullerton, CA


    Crap, I totally forgot... it's finals week at my college.

    A Firefly MIGHT be able to fit in that small chassis of yours.

    I'll measure the transformers I used on mine and see how much space it all takes up. The guts space (caps and resistors) might be an issue too, but doubtful.
     
  13. Jukebox

    Jukebox Gretschified

    Age:
    64
    Jun 2, 2008
    Foreston,MN
    I really think with a five inch speaker and wanting clean sound.It will have to be 1/4 or 1/2 watts?
     
  14. JohnnyCrash

    JohnnyCrash Gretschie

    336
    Nov 22, 2008
    Fullerton, CA


    The Firefly can be built in a lower gain version, but it distorts way early compared to even a Champ.

    It can be run "clean" though.
     
  15. mugsy

    mugsy Synchromatic

    766
    Nov 3, 2008
    Indiana
    Yeah, I'd like to see what you did--especially which components you settled on.

    In my effort to reduce hum, I made a couple of changes which included an NFB. I may disconnect it now that I've added some shielding to regain some gain. I didn't think about adding the bypass cap... I was all set to add an MV or l-pad :) Thanks for the suggestion.
     
  16. JohnnyCrash

    JohnnyCrash Gretschie

    336
    Nov 22, 2008
    Fullerton, CA


    Do the Gibsons have a center tap for the 6.3 volt heater taps?

    If not, wire a 100ohm resistor to each heater wire and have that end at the power tube's cathode (before the resistor and bypass cap). This forces the 6.3vAC heaters to float on top of a negative DC voltage (the power tube's cathode). This reduces hum bigtime. It's called "DC elevating" the heater supply.

    As far as the diodes, I don't remember which ones I settled on. I know for my "asymetrical" clipping position on the switch I used two 1N4001's in one polarity and a single 1N4001 in the opposite polarity right off of the coupling cap to ground that fed the Volume pot.

    The other setting on the switch I forget the diodes I used. I might have used LEDs in this spot.

    As for the cathode caps, I left a 25uF in V1 triode #1 and put a switch to put in a 0.1uF (or maybe it was a 1.0uF) in on the second triode's bypass.

    I actually prefer NF. I know that technically speaking NF is "defeated" when the output section clips or overdrives, and this is true when it comes to the amount of "rawness" in the overdrive (or level on the dial when it starts to overdrive), but at the same time the frequency response is still widened even when clipping. Brighter and deeper. Therefore I always use NF for it's frequency benefits on tone - even if I want a rawer overdrive earlier on the dial.

    I have a 5f! tweed Fender Champ build that has NO bypass caps in the preamp at all and it is a very clean sound. I like it for warm cleans and actually for recording Bass through a 1x15" Jensen AlNiCo P15N when I find it's sweet spot that doesn't fart or distort.
     
  17. mugsy

    mugsy Synchromatic

    766
    Nov 3, 2008
    Indiana
    The GA-5 does have resistors to reduce filament hum. I think my problem was unshielded wiring and an unshielded cabinet. I also converted it to star grounding. I'm not sure what made the most difference, but it's very quiet now.

    I tried the 1N4001s. It worked, but the sound was "fizzy." Adding resistors seemed to smooth it out, but lessened the effect. I didn't have time to tweak it much (I was on baby duty this afternoon), but I'll try some different combinations when I get a chance.

    The cap on the cathode of V1b was a HUGE improvement. It really brightens up the amp along with adding significant gain--much more to my liking :)
     
  18. JohnnyCrash

    JohnnyCrash Gretschie

    336
    Nov 22, 2008
    Fullerton, CA
    Yeah, the diode thing is more of a "volume convenience" than a "tone mod."

    I personally dislike the diodes AND the 2nd bypass for "good tone", but it does help take an extremely basic amp and add gain and treble in a pinch - especially when you need a 5w even quieter.

    Low/High inputs are likewise just as useful in a one knobbed 5w amp. Try a lower value for the High input's input/grid resistor. Heck even try no resistor and use ferrite beads to filter out radio interference instead of the 68k resistor. It opens things up and hits things a little harder in the front end to boot.

    The great thing about the cap and diodes is I can switch them off and just run the amp stock.
     
  19. Jaybird

    Jaybird Electromatic

    38
    Nov 2, 2008
    California
    Can this also be used on a 5F1 circuit?
     
  20. mugsy

    mugsy Synchromatic

    766
    Nov 3, 2008
    Indiana
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