Followup on AB165 Bassman filter caps.

Discussion in 'Amp Tech Center' started by Paul G., Sep 13, 2019.

  1. Paul G.

    Paul G. Friend of Leo's

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    I recently serviced my AB165, clean, inspect, tighten tube sockets and all new electrolytics.

    I was surprised to find the first stage had 250uf caps instead of the Fender spec 70uf.

    I figured the last tech who serviced the amp (I believe it was Tony Bruno back when he was a local repair guy) just put in whatever was lying around, so I put in the modern equivalent 80uf.

    Testing the amp it didn't sound right, the bass was not as tight, the amp wasn't as punchy and I definitely could hear some ghost notes around D on the scale.

    On the advice of Wally and Commodore 64 on this forum I went just installed a pair of 220uf caps instead -- in series so 110uf instead of 40uf.

    BOOM! She's back! Clear, punchy, loud and dripping with syrupy goodness!

    I guess Tony was doing the boutique thing back then too, making the amp better with some heavy filtering.

    Thanks Tony, Wally and Commodore 64. I learn more every day.

    One of my favorite amps, wish it was lighter and smaller -- nowadays you walk into a club with a head and cab, you get the stinkeye.
     
  2. Phrygian77

    Phrygian77 Tele-Afflicted

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    I used the 100uF F&Ts in my AA165 build. I gig with it all the time, although I built mine as a 1x12 combo. I also upped the PI input cap from 500pF to 1000pF.
     
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  3. Phrygian77

    Phrygian77 Tele-Afflicted

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    [​IMG]
     
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  4. Paul G.

    Paul G. Friend of Leo's

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    I'm thinking of getting a combo cab for it so I can gig with it. I can always swap the chassis back into the head shell if I want to.
     
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  5. schmee

    schmee Poster Extraordinaire

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    I wonder why it was that way? Is there something about the BF architecture that causes that? I've had SF Bassman's with stock Filters that are super clean. In fact, the AA371 is my favorite for loud and clean of the Bassman head's. The filter values and related resistors are identical AA371 vs AB165 on the schem. Maybe it's in the PI somewhere...?
     
  6. radiocaster

    radiocaster Poster Extraordinaire

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    Why would you want a combo cab if you complain about the weight? Get a smaller cab instead, it might look funny as a t-shape if you put the head on top, or put the cab on top of the amp. Who cares?

    Or get a 2x10".
     
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  7. Wally

    Wally Telefied Ad Free Member

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    Paul G, I like stories of comparisons. However, ime, good 80mfd caps in series do not yield any problematic ghost notes. It is a different Sonic compared to larger caps, but I have to think that you had a weak cap in that pair. Yes...new caps can be weak or bad.
    I consider the first stage of filtering to be the beginning of tuning an amp for what one wants.
     
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  8. Wally

    Wally Telefied Ad Free Member

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    Here is a neat 2X10 combo I put together.....1964 Dual Showman in a Fender Pro Sonic cab.
    ACCF1CEB-9C50-4654-8E84-79012762D0E7.jpeg



    And just for fun... here is my other ‘motorcycle’....the motor is not shown because I was taking the picture!!!
    D5A7AFDD-85CC-449B-A5C5-72C17939B6A8.jpeg
     

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  9. Paul G.

    Paul G. Friend of Leo's

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    I always check caps before install them.

    Unfortunately I'm testing them at like 3V. If there's a problem at ~300V, I can't know until they're in.
     
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