1967 Fender Bassman Ab165 Help.

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Fltwrench, May 19, 2015.

  1. Fltwrench

    Fltwrench Member

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    Hello,
    I have a I believe a 1965 Fender Bassman Head that belonged to my father. I think it is a AB165 circuit? It was completely stock original but was rather noisy. I had an amp tech take a look at it for me to test everything out. I told him if he could get the amp to "break up" a little sooner that would be good. I'm looking for help because I have no idea what he actually did to it as far as MODS / cap replacement / etc.. I see there are still some blue molded caps left, there is also a blue molded cap attached to the ground switch, but obviously some of them were replaced. Can anyone tell me what was actually done to this amp? What parts would i need to buy to return it to original specs? I'm worried that my amp tech jacked some of the goodies and replaced with crap. I can post more pics if needed. Thanks All !!

    View attachment 234 View attachment 235 View attachment 236 View attachment 237 View attachment 238
     
    Last edited: May 19, 2015
  2. axpro

    axpro Member

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    Hey replaced some noisier caps by the looks of things.... Orange Drops are pretty common for Fender circuits, the Mallory caps (yellow ones) look new. but without knowing how original it "was" i don't know for sure. It may have been stock, but was it all original? Does that matter? The parts used on the board seem to be common good parts. Not crazy "holy grail" parts, but the sort of stuff i build amps with for myself, as with lots of professional repair guys. Does it sound bad now? Why are you so worried? If you asked him to make it break up earlier, he would have modded it. WIthout seeing values I don't know how much. I severely doubt he jacked any of the parts, as it's an ancient amp and to be honest they are ALL WAY PAST THEIR ESTIMATED LIFESPAN! These amps weren't designed to last 50 years. They weren't even designed to last 20. The parts get old and drift, it just happens. and old worn out parts aren't good for anything. New Old Stock parts? Maybe, but old worn out parts??? Nope. just junk. The big changes would most likely be in the power supply filter caps. Don't remember where they are on blackface bassmans, usually under the bottom of the chassis in a little seperate box on most fenders. THOSE he would have definitely changed for newer and less noisy parts.
     
  3. axpro

    axpro Member

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    If you are worried that it doesn't sound the same... IT WON'T.... EVER to be honest. That amp sounded like it did BECAUSE the parts had drifted off of their values. Without knowing what each part had drifted to specifically, and how much the old power caps were losing as far as voltage handling, the circuit is different now. Not always necessarily worse, but different. If you have really good ears, you can hear the difference between cap brands (apparently) I can't tell much difference with a single cap, but cumulatively there is a noticeable change. Again, not "worse" just different. If you want original era parts that are just like what was taken out, prepare to shell out a LOT of money to find New Old Stock replacements.... that might sound better... or worse... but most likely very slightly different.
     
  4. donnyjaguar

    donnyjaguar Member

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    I see a bunch of resistors have been replaced. He probably went through all the components and replaced anything that was out of specification.
     
  5. Fltwrench

    Fltwrench Member

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    Thank you for your help, I really appreciate it. I know for a fact that it was 100% original when I had the amp tech look at it. Original tubes and all, wasn't a orange drop anywhere. Now I am wishing I would have gotten all the parts that he replaced back. Amp sounds sterile now and wont break up for nothing.
     
  6. TimmyP

    TimmyP Member

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    Shouldn't those two white Mallorys have been replaced?
     
  7. garret

    garret Member

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    They break up a bit at high volume, but for the most part are very clean amps.
     
  8. xtian

    xtian Member

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    An amp tech should give the owner ALL the parts he/she removes, even if they are blackened lumps of carbon.

    But you didn't say the most important thing: how does the amp sound now?
     
  9. Fltwrench

    Fltwrench Member

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    I didn't ask for the old parts back so that's my fault I suppose. It sounds sterile. Doesn't really start breaking up like I had hoped. When dimed it does break up some. I just wish I could figure out how it differs from stock now. Are just a few components updated or is it a modded circuit.
     
  10. xtian

    xtian Member

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    Just shout if I'm pointing out the obvious, but why not download the Fender layout, and compare the components yourself?
     
  11. Fltwrench

    Fltwrench Member

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    Yes indeed I need to do that. I posted on here because I know there are people on here who have much more experience than me and prob know this circuit like the back of their hand. I know very little about electronics. I was hoping just by people looking at my pics they may be able to shed some light on how this thing is put together now. I appreciate all the insight. I suppose it could be a good way for me to start a new hobby, dissecting this amp that is.
     
  12. axpro

    axpro Member

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    Yeah, your tech SHOULD have given you a little bag of parts that he removed, whether you ask or not. When i repair a guitar and pull bad pots, or components i leave them in a bag in the case... Just so that the customer has them in case they want all the original parts. Did you go to a tech who deals with players? or someone who specializes in old Fenders? I just ask because literally ANYONE could fix a bassman, it's a very simple circuit. But if it's not a player, he will fix it, check it on a scope and pronounce it "in spec" (I know a tech or two like this) If it's a player or someone who understands guitar players, he (or she!) is usually all about making sure the amp "sounds right" instead of performing correctly. A Blackface Bassman, performing "correctly" is not always a great amp for everyone. I had one that had been restored, and i didn't like it. I found an old one in a junk shop and it sounded WAY better, to me at least... all because the components had drifted in a way that made sense to my style and my brain.

    There are no "magic" parts, i.e. your old components. Orange drops work just fine to make a nice sounding amp. You just need to be working with someone who shares your idea of what a Bassman is supposed to sound like. Blackface Fenders were CLEAN MACHINES for the most part... though i''ve played a few old amps that really kick it up a notch, due to parts being way out of spec.

    Good Luck sir. I am sure in Nashville there is a tech somewhere who will be able to tweak it to your liking.
     
  13. Kyle B

    Kyle B Supporting Member

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    It does appear to be AB165 by the presense of the the two 220k feedback resistors. Hard to say exactly what you have there without really analyzing it though.

    Um - VERY VERY BAD if this is indeed still in the circuit. This is the fabled "death cap", and if your amp tech returned this amp to you with that cap still active, he needs to have the amp taken back to him and smashed over his head. Well, not literally, but that is a remarkably stupid thing to leave behind. Take a better picture of the power input section so we can see if it's actually still connected or not please.
    Hope you at least got a 3-prong plug on it now.....


    If you REALLY want this head to rock, consider this mod:
    http://acruhl.freeshell.org/mga/main/AA864_vs_AB165.html
    It takes the best characteristics of the AB165 and AA864 and combines them together to make a tone machine of monstrous proportions :)
     
    Last edited: May 23, 2015
  14. swiveltung

    swiveltung Member

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    He left those great blue caps in the bass channel, but unfortunately removed them from the other channel. I would try to get them back. (they are worth about $20 apiece for one thing)As best I can tell from the pics, the white caps are new replacements. They come in yellow or white depending on values etc. Which number on the Orange Drops? One version is known to be a bit sterile sounding. It should be a number something like "716P" etc.
     
  15. axpro

    axpro Member

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    Perhaps did he make the "Normal" channel break up more? You mentioned that you asked him to make some changes... Things certainly have been changed.

    As for the blue caps and relative value... Who knows. If they were out of spec, or starting to fail, they are not "worth" anything in my book. black magic or voodoo be damned. As i said earlier, depending on the type of tech you went to, it might simply be "Those parts were out of spec, these parts are in spec" I worked with a guy like that in the past. He tested mainly with a scope, and a little sears test guitar with a humbucker... with 3 strings tuned to a triad. he couldn't play a note! It was all about "working to specification" and not "sounds good" Because sound is subjective. If the old caps are really important to you, call the shop. see if they are in a pile of junk parts or something. they may be,
     
  16. Fltwrench

    Fltwrench Member

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    I believe this is the death cap? I do have a 3 prong plug. View attachment 370 View attachment 371
    View attachment 367
     
  17. Fltwrench

    Fltwrench Member

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    Orange drops.... View attachment 375 View attachment 374
     
  18. Fltwrench

    Fltwrench Member

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    Could you tell me which blue molded caps i would need to purchase? The ones I am missing? View attachment 376
     
  19. Fltwrench

    Fltwrench Member

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    Wow that MOD looks interesting I am going to look into that. Any idea what blue molded caps are missing from my layout? View attachment 377
     
  20. Fltwrench

    Fltwrench Member

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