Sell or mod my 64 bassman AA-165?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Rock-On!!, Dec 15, 2004.


  1. Rock-On!!

    Rock-On!! Member

    Messages:
    491
    Joined:
    Jan 22, 2004
    Location:
    The Crossroads
    I have just acquired a low powered twin tweed clone. The normal channel inputs are voiced pure tweed, the two bright inputs are voiced #1 blackface #2 slight plexi. This amp is also set up for fixed bias or cathode bias and will run 6L6s or EL34s, run one rectifier or two. So I have a lot of tonal options in this amp. Which leads me to the question of do I mod the AA-165 bassman I have to get a Marshall OD tone with a master volume or sell it and have an 18 watt built. I am looking for good classic Marshall tone at volume levels for home use. Money is an issue so modifying the bassman would be the cheapest way out, but I am not sure I could achieve the outcome I am looking for . Have any of you had success modifying a bassman like this? If so do you have any links that you might point me to.
    Any thoughts or suggestions welcome.
     
  2. TheAmpNerd

    TheAmpNerd Member

    Messages:
    1,063
    Joined:
    Sep 23, 2004
    Location:
    Tejas
    Rock on,

    That is great on the low powered tweed twin clone.

    So then obviously you don't want another blaceface
    tone. You are on a budget, so I would mod that little
    head that you have. You'll get the most bang for the buck
    that way too.

    Success, indeed. I've done a few of these and the guitarists love'em. In fact it makes most of the Marshall
    friends jealous too. : )

    Where in Texas are ya located?

    email me at NOspikeoneSPAM at NOSPAM airmail dot net.

    Remove NO SPAM to send.

    or we can try out the new pm feature here.
     
  3. Rock-On!!

    Rock-On!! Member

    Messages:
    491
    Joined:
    Jan 22, 2004
    Location:
    The Crossroads
    TheAmpNerd,

    Sounds like a good idea. I tried to email you but it bounced back.
    I will try to give you a ring Thursday.
     
  4. John Phillips

    John Phillips Member

    Messages:
    13,080
    Joined:
    Mar 17, 2002
    Location:
    Scotland
    Do NOT mod that amp. It's a very rare model - FWIW, it was made only for a month or so in very early 1965. Notice both it and the AB165 circuit have January 1965 dates codes, that's what the "165" means. Sell it to someone who cares about old Fenders, and buy a real Marshall or a good clone.

    If it was a later SF Bassman (or maybe even a later BF AB165), there are thousands of them and it isn't any great loss, although I wouldn't personally mod any BF amp these days. The Bassman isn't the most desirable, but it's still not geting any more common, or any cheaper.
     
  5. TheAmpNerd

    TheAmpNerd Member

    Messages:
    1,063
    Joined:
    Sep 23, 2004
    Location:
    Tejas
    Yeah, good point, I didn't think of that.
    Trying to figure what that might fetch...
    Then get a later model bassman to mod.

    Thinking anything descent is probably going to
    cost more then the baseman to start with so
    it is kinda a no win, unless he buys a crummier
    bassman to build from.

    He has budgetary constraints..any good Marshall
    is going to fetch some $$$$ a good clone too.
    And it sure as **** ain't going to be worth it
    to dig into a TSL now is it?
     
  6. Swarty

    Swarty Member

    Messages:
    1,143
    Joined:
    Dec 16, 2003
    Location:
    Michigan
    I disagree about that amp being particularly rare, it does however, bear the infamous distinction of being the first Fender model to be screwed up by the CBS era regime! Yippee

    Here is a link to some HC reviews of a Marshallized Fender mod I've developed and performed on scores of amps just like yours.

    CLICK HERE TO SEE HC REVIEWS
     
  7. Jon Silberman

    Jon Silberman 10Q Jerry & Dickey Gold Supporting Member

    Messages:
    35,174
    Joined:
    Jan 3, 2002
    Location:
    Northern VA
  8. 908SSP

    908SSP Member

    Messages:
    5,794
    Joined:
    Jun 22, 2004
    Location:
    Michigan
    My Bassman says AA165 on the paper chassis tag. PE stamped on the tag, is that the date code? I had it repaired, it had been repaired before with the wrong resistors and some wrong capacitors, now it is back to stock. I haven't had it that long so am learning new stuff about it all the time. Looking forward to this discussion.
     
  9. Swarty

    Swarty Member

    Messages:
    1,143
    Joined:
    Dec 16, 2003
    Location:
    Michigan
    The AA165 got the screwy bias balance circuit and the AB165 added the 220k feedback resistors.
     
  10. Rock-On!!

    Rock-On!! Member

    Messages:
    491
    Joined:
    Jan 22, 2004
    Location:
    The Crossroads
    The tube chart reads AA-864, but when I took it in for caps and tubes the tech sail it is an AA-165.
    Here are a couple of pics
    [​IMG]
    [​IMG]
     
  11. fullerplast

    fullerplast Senior Member

    Messages:
    6,793
    Joined:
    May 5, 2003
    I wouldn't modify that amp either. You will not get a convincing 18W marshall tone out of it IMHO. You should be able to get a decent amount of cash for that amp (although some of your signal caps have been replaced unfortunately) and with a little more you can pick up a used 18W or something like a Winfield or Pete Cage which are both great bang for the buck. They also sound really good! There are plenty of kits out there if you are so inclined as well.

    Here's the link for Winfield:

    Winfield
     
  12. TheAmpNerd

    TheAmpNerd Member

    Messages:
    1,063
    Joined:
    Sep 23, 2004
    Location:
    Tejas
    I guess modify is the word eh?

    The amp has already been worked on already.

    It is obvious that rock on isn't too happy with the
    amp as it sits, otherwise he wouldn't think about
    doing anything with/to it.

    It is not original either, so we can dispense
    with the collector value argument too.

    The pics show a couple of my pet peeves too.

    1. The way the power cord was installed.


    2. The output socket "fix". If you are going to
    do one, do them both.


    Still the most bang for the buck is to make it into
    some cool amp he'll use and be happy with.

    AND

    You can do it without drilling holes in it.

    So why not?
     
  13. Jon Silberman

    Jon Silberman 10Q Jerry & Dickey Gold Supporting Member

    Messages:
    35,174
    Joined:
    Jan 3, 2002
    Location:
    Northern VA
    Because, as fullerplast has already correctly noted, he's unlikely to get the results out of it that he's seeking ("a Marshall OD tone with a master volume"/"good classic Marshall tone at volume levels for home use").

    Add my vote to the folks advising Rock-On!! to sell the Bassman and buy what he really wants.
     
  14. Rock-On!!

    Rock-On!! Member

    Messages:
    491
    Joined:
    Jan 22, 2004
    Location:
    The Crossroads
    After giving it some thought, I think that a low watt clone would be the best way to go. I do like vintage gear, but if it doesn’t and can’t do low volume Marshall then off to ebay it will go. Now, that leads me to my next question. I have read a lot of good things about GDS but the price is a little out of reach. I have a contact that can get me the Mojo kit for about $350.00 less, Has anyone here built one or have any experiences with the Mojo kits.
    Thanks,
     
  15. John Phillips

    John Phillips Member

    Messages:
    13,080
    Joined:
    Mar 17, 2002
    Location:
    Scotland
    Yes, quite extensively. There's a still a difference between that and 'modding' though. What's been done (although largely unnecessary and potentially tone-changing, in the case of the coupling caps) is still 'maintenance', and in any case could be put back to stock very easily.

    Yes... I'd agree with both of those. I'm also unhappy with the way the screen-grid resistor is touching the wire from the PT.

    It's got the wrong knobs too... ;)

    Still, I would guess that the most bang-for-buck is to sell it (it's still got some collector, or at least old-Fender-enthusiast potential) and buy something else.

    Nah, that's an in-house screw-up. Although CBS did buy Fender at the start of 1965, I doubt they had a team of engineers lined up and waiting to get in there and mess with the products in the first few days!

    What's interesting is how many amps they must have been cranking out then - the AA165 was made for only about a month, and yet isn't impossible to find. The AA864 is almost common, and that was made only from August '64 to Jan '65... five months at the most.
     
  16. Swarty

    Swarty Member

    Messages:
    1,143
    Joined:
    Dec 16, 2003
    Location:
    Michigan
    Lessee, this amp revision was January 1965, when CBS took over Fender, and the revision included the first of many "enhancements" associated with the CBS era that culminated in the '68/'69 silverface abominations that included not only the AA165s bias/balance, but the partial cathode bias and suppressor caps caps through out the circuit.

    OK, perhaps if I reworded it without reference to CBS (although it may be difficult to prove or disprove the association).

    How's this:

    The AA165 bears the dubious distinction of being the first Fender amp to incur circuitry changes more often associated with the silverface amps that came out years later.
     
  17. Rock-On!!

    Rock-On!! Member

    Messages:
    491
    Joined:
    Jan 22, 2004
    Location:
    The Crossroads
    Ok, I am no electronically challenged when it come to technical stuff, can you point out the issues in more detail. What is wrong with the power cord, output socket and the screen-grid resistor? Can these things be easily fixed? I do have te original knobs.:D

    Thanks again for the feedback:dude

    What Marshall or clone would you recommend for jamming at home with friends, couple of guitars, bass and Roland V electronic drums. I am looking for an amp that can pull off early Clapton to Gary Moore and Slash tones. Does this amp exist?
     
  18. John Phillips

    John Phillips Member

    Messages:
    13,080
    Joined:
    Mar 17, 2002
    Location:
    Scotland
    That's OK, the knobs seriously affect the tone and you should put them back immediately ;).


    The power cord being connected with a 'chocolate block' is not good. It should have been stripped back further, then the core wires taken directly to the AC outlet. The screws in those little terminal blocks can work loose with time.

    I can also see that the 'death cap' appears to be still present on the ground switch, even though the cord has been replaced with a 3-wire... get rid of that.

    On the output socket, the new screen-grid resistor should be mounted directly above the socket (like the original one on the LH socket in the pic), with its leads as short as possible to stop it flapping around and stressing them. Also, it should (ideally) be a wire-wound type - that's a metal-film by the look of it. Wirewounds are the most robust when it comes to short-term overloads (like when a tube blows) and so more reliable. Also, if a tube does blow, that resistor will get very hot, so having a wire touching it is very bad practice since the wire insulation will melt.

    Plus, as TheAmpNerd said, if you're going to change the resistors on one socket, do them both! Long-term heat cracking of the original carbon-comp resistors (both the screen-grids and the smaller grid-stoppers) is a known issue on old Fenders. That amp's been 'fixed', not 'serviced', in other words - most likely one or both of the replaced resistors broke.

    Oddly, someone has gone to the trouble of changing almost all the original coupling caps, which was almost certainly not necessary. These are the yellow caps on the tag board. Changing the electrolytic caps (the small black ones) is a good idea - and it's been done, including the bias cap (often overlooked) but they've left the carbon-comp bias feed resistor, which can also be a good idea to replace...

    Even more baffling, although they've changed most of the caps in the tone stacks (I've never seen one of those fail, ever) they've left the two phase-inverter-to-power-tube ones (the red ones at the RH end of the board), which are about the most commonly prone to leakage and the ones that cause the most serious trouble if they do!

    Maybe done by more than one tech... it's quite random and not very logical, anyway.
     
  19. John Phillips

    John Phillips Member

    Messages:
    13,080
    Joined:
    Mar 17, 2002
    Location:
    Scotland
    Given that the circuit must have been finalized at the start of January 1965 - or else there wouldn't have been time to make any significant quantity of AA165s before the AB165 revision later that month - I'd take a bet that it was developed before the CBS buyout. Not only that, I really don't think any serious personnel (or design practice) changes happened immediately. Certainly not within days. I think it's unfair to blame CBS for everything that went wrong at Fender - they didn't help, but there are plenty of things that were definitely the fault of the previous regime too... for one, who do you think designed the infamous 3-bolt Strat neck? Leo Fender :eek:.

    Most of the first obvious CBS features of the guitars started to come in mid-'65, so I'd think it's more likely that any CBS-inspired amp changes began about then too. I certainly don't think they came in on Jan 5th 1965 with orders to immediately downgrade and mess up everything.

    I'd agree with that. I think sometimes these days it's hard to remember just how quick all these changes were though. We talk about the 'classic BF period' as if it went on for ever, but in fact it was less than five years - three of which were under CBS.
     
  20. Rock-On!!

    Rock-On!! Member

    Messages:
    491
    Joined:
    Jan 22, 2004
    Location:
    The Crossroads
    For those of you that know waht the numbers mean I will post them.
    Part #125P7D is 606-502
    Part # 125C1A is 606-4-45
    Part # 125A13A is 606-512
    Chassis serial # is A 05252
    Here is a link to the transformers.

    [​IMG]

    [​IMG]
     

Share This Page