Need some guidance on a BassmanAB165

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Gmc, May 25, 2015.

  1. Gmc

    Gmc Member

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    Hello all,
    Hoping you can help. I have a bassman head AB165. I have it it for a few months, it was playing up, a little craking static sounds. I believe it had some unspecified mods to it when I bought it. It sounded pretty good. Not 100% the sound I was looking for but heading in the right direction.

    So I took it it the local amp repair place not going to name names I am sure they are perfectly good. Had a Few discussions about the amp I thought it was the power tubes going but apparently not. Long and short of it we decided to put it back to stock and start again as apparently some crazy stuff on the inside. So I have it back and thinking of taking it in to get some mods, I have done a lot of research and am now feeling far more in the know ( might do it myself but may just get the guy to do it).

    The issue at hand!!! At last. The amp has completely lost its soul. It sounds completely sterile and the highs are shrill and terrible. Unfortunately this is the second time this has happened. I took in a musicman sixty five with so much personality, it came back like it had a labotimy. It's the same shop but have no idea if it's the same person who worked on it. I even changed the tubes which helped a little but the magic is gone. So now I have two amps that sound as exciting as a kick in the head.

    No cracking sounds very quite except no soul.

    Pleas help, what to do? Does the ab165 really have no personality whatsoever stock? I just cannot believe it could be that bad. (This is all for guitar by the way) the mods I was thinking of are the hybrid AA864/AB165
    Some guidance please. 1st post so be kind! Thanks in advance.
     
  2. Blue Strat

    Blue Strat Member

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    Post a few photos of the inside of the amp. There may be something we can spot right away.
     
  3. Gmc

    Gmc Member

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    Here are some photos. I actually have a photo of before work was done. One thing I did notice was the connection from the volume to the 7025 tube. On the layout it goes from the bright switch instead. I have had a look I can see he added back the 220k feedback loop. Maybe some of the resistors are the wrong value.

    Has this been converted to a true bias? I was going to get that done if it had not.

    Thoughts would be appreciated.

    Cheers

    George



    i View attachment 1523



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  4. smolder

    smolder Gold Supporting Member

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    One man's sterile could easily be another man's sparkly cleans. If it was modded to achieve a high gain distorted sound, they may have just put it to "no balls" stock. Could also be a matter of a colder bias than you prefer.
     
  5. Gmc

    Gmc Member

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    Understood. I know a lot of this is subjective. But those highs are really unpleasant and unmusical. I need to figure out how to bias it also.
     
  6. Blue Strat

    Blue Strat Member

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    Looks like it's true bias now. Not seeing anything jumping out. This is probably a situation where you need a tech, who knows what these are supposed to sound like, working on it. Besides that, I got nuthin'! :)

    What speakers are you using? They could be part of the unpleasant brightness.
     
  7. garret

    garret Member

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    Have you jumped the channels together?
     
  8. jaytea4

    jaytea4 Supporting Member

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    speakers/cab type? ... preamp tubes (V1)? ... bias (plate voltage/current)? What sound were you "looking for"?
     
  9. Gmc

    Gmc Member

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    I am currently playing it through the speaker in my musicman amp, so nothing fancy.its an Alnico. I have taken it into a good shop here in town and played it through an Austin Speaker Works 2x12 kts 60. Sounded amazing before the "fix" not so great anymore. When the amp sounds good I will go and blow some money on a cabinet but not before.

    I have jumped the cables the shrill high end is still an issue.

    Does the patch going from the volume instead of the bright switch make any difference.? 1st photo. Would removing the capacitor at the volume help?

    Well, I might as well go ahead with the aa864/1b165 hybrid and see where I land.

    Are the mods easy to do for someone who has not touched a soldering iron since I was 16? So 20 yrs. Or should I get a tech?
     
  10. Gmc

    Gmc Member

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    Speakers as above Musicman Alnico. Preamp tubes are(looking at the back going right to left from the power tubes) ECC81 JJ TUBE, THEN 2X FENDER 12AX7WA (Really faint text so the "A" might not be an A), THEN SOVTEK 12AX7 WC.

    Where do I take a measurement for the bias? I have a volt meter just have not figured that out yet. Took me ages to figure out the Musicman amp.

    Sound I am looking for is to have some great cleans, Jeff Buckley clean tele sound, with ability to get some great dirt at about 4-5 on the volume or heading that way, adding "Soul Food' Overdrive pedal to get the rest. I love the low end on the bassman generally it just has such a rich tone throughout the bass up to the trebles.
     
  11. Blue Strat

    Blue Strat Member

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    Your best bet is to discuss with the tech how the amp changed, for the worse, with the work done. Since we can't hear it it's kinda pointless to speculate.
     
  12. Gmc

    Gmc Member

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    Thanks Mike. I will do.
     
  13. AL30

    AL30 Member

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    Any pics of the filter caps? If they're too big the amp can sound stiff. I'm also not a fan of the 220K resistors on the power tubes. And I'm sure you're gonna get differing opinions on this but - I don't like using those particular Orange Drop caps in Fenders. I much prefer to use Mallory 150's. The OD's (715/716) sound sterile to me and there seems to be a bit of an annoying high end spike to my ears. But, as Mike said, talk to the tech first. Let him know what you're looking for and go from there.

    AL
     

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