Two '64 blondes. Two different sounds ... why?

Discussion in 'Amps and Cabs' started by gnugear, Jun 14, 2006.


  1. gnugear

    gnugear Member

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    My buddy brought in his '64 blonde bassman so we could comapre them. We played through the same vintage '62 cab with Jensen P12Ns.

    His has a wonderful bloom, depth, and detail that's lacking from mine. It almost has a tweed vibe to it. At first we thought it was the tubes but after swapping them around, the results were the same.

    We flipped them over and the circuits are the same. All original parts except for the electrolytic bypass caps. All of the filter caps on mine were swapped out for Spragues. He has two filter caps swapped and replaced with 200uf which seems pretty high. If anything I thought that would result in a stiffer tone. But it's just the opposite of what I hear with mine.
    What gives? Component value drift? Anything else?
     
  2. GuitarBrent

    GuitarBrent Member

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    Is your amp biased properly? Did you rebias when you swapped tubes?
     
  3. gnugear

    gnugear Member

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    Wow, I think we just found it.

    The two resistors off the phase invertor are supposed to be 100k and 82k. My 100k is 1000k. Someone at Fender was sleeping when the wired it.

    Can't wait to try it out again tonight.
     
  4. VaughnC

    VaughnC Supporting Member

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    A few things come to my mind:

    1) All electronic componants are born with tolerance ratings....some as high as 20%. So, if one amp's componants happen to lean towards the high side of their tolerance and another amp tends to lean towards the lower side, I would expect to hear some difference.

    2) Componant aging: componants can & do age and can drift out of their original tolerance rating. Capacitors can also develop leakage and thus can behave more like a resistor.

    3)Wiring layout: the relative position of any flying leads can result in different capacitance between the leads themselves and the chassis....resulting in different tone.

    4)How the amp was played during its life. I would expect an amp that was played at fairly low volume with cowboy chords all its life would end up sounding different than a blues/rock guy playing a similar amp full out most of its life. Even though it probably can't be measured, guitar amps seem to take on an imprint of what they experienced in their life.
     
  5. VaughnC

    VaughnC Supporting Member

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    Huh, 1000k? 1000k=1 megohm.....are you sure you're reading this properly? Or are you saying the original 100k has increased in value to 1 megohm (which is possible)?

    100k is brown-black-yellow.
    1000k or 1 megohm is brown-black-green.
     
  6. gnugear

    gnugear Member

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    Yeah, I read it wrong. I saw that the gold band is for tollerance, so it should actually be more accurate than the ones with the silver band. :(

    I'll measure all the resistors tonight and see what I get. I suppose there's no easy way to tell if a cap is leaky?
     
  7. pep

    pep Member

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    Actually, a lot of the time they look like they are bloated at the top and may or may not have some corrosion or fluid on it.

    One other thing. Did you check to see that you have the same choke, power and output tranny's?
     
  8. Ian Anderson

    Ian Anderson Member

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    I wanted to have mine tweaked by Billy Zoom who does Setzers but he's been on the road for a while now. :(
     
  9. Blue Strat

    Blue Strat Member

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    You should measure all resistors and plate voltages and compare them to the "good" sounding amp. Somewhere in these numbers lies the answer to this mystery.
     
  10. Blue Strat

    Blue Strat Member

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    Electrically leaky capacitors, more often then not, show no visible signs. 45 year old electrolytics should be replaced.
     
  11. John Phillips

    John Phillips Member

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    What Mike said... but even then you may never get them exactly the same. A long time ago I had two Fender Super Champs that I used as a stereo rig. They didn't sound the same - one was more "bluesy" (dirtier and more midrangy) and the other more "rock'n'roll" (brighter and cleaner). I tried swapping tubes, speakers - even the cabinets - measuring everything and changing parts (although there were surprisingly few real differences)... but still they sounded different. In the end I just put a blue jewel light on the 'bluesy' one so I would know which was which :).

    I've noticed it with most of the (particularly vintage) amps I've worked on too - they just don't all sound the same. Once you've eliminated major parts variation, I think wiring layout makes a big difference - it's noticeable that Hiwatts (which have the neatest wire dress of just about any amp) are in my experience significantly less variable than (say) Marshalls, which are much more loosely laid out. Component tolerances do as well, even if you measure things I'm not sure you're always seeing the precise characteristic that affects the 'tone' - eg with caps, the value may be less important than the variations in internal structure, if something I read about this (by a cap manufacturer I think) is true.

    But these are relatively small difference compared to what (I think) you're describing, so it's definitely worth measuring as much as possible if you have a reference amp that sounds that much better. Don't assume the effect filter cap values have either, trust your ears. I've never thought underfiltering sounded that good, despite what's often said.

    Another problem which is quite common on old Fenders is board conductivity. This can have a HUGE effect on tone, and in some cases make the amp unstable even if it doesn't just sound bad, but it's a very difficult thing to measure or even trace sometimes. Try undoing the eyelet board on your amp, and lifting it clear of the underlayer - support it on some bits of wood or something - it seems to be more commonly a problem with the underlayer than the main board. If this does make a difference, you can fix it more permanently.
     
  12. Blue Strat

    Blue Strat Member

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    Hey John, you reminded me of something. Have you ever noticed a Fender board, particularly a '70s was coated board, robbing an amp of high frequencies? I have both a Vibrolux Reverb and a Princeton Reverb that both are lacking in highs compared to others I've heard. I've done lots of work on these amps and still haven't gotten them to sound "right".
     
  13. John Phillips

    John Phillips Member

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    Yes, absolutely. This is one of the common 'bad tone' results, presumably caused by unintended negative feedback somewhere - the other is odd 'honky' resonance or very nasal tone, presumably caused by positive feedback.

    For years I could never work these out, then after I started getting a few through that were actually unstable when definitely the stock circuit (so they couldn't have left the factory like that), and struggling to find the cause, I found out about the board-conductivity problem. After that I started coming across it a lot more often when I checked for it, and noticed the effect it was having on the sound below the point of instability.

    The interesting thing is that it's almost always the underlayer - it seems to develop the problem first below the 'points' of the component leads poking through the eyelets above. I cure it simply by fitting a new insulator between the two boards - thick card is plenty good enough. On the rare occasions where it's actually been the main board, I've removed the electrolytics and heavily heated the board with a hairdryer, adding more wax - which sort-of replicates Fender's original 'baking' process and seems to do the trick.
     
  14. slider313

    slider313 Silver Supporting Member

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    Mike,I rewired a '71 Vibrolux, a while back,to blackface specs.and when compared to the '66 it didn't even come close. I even ran a speaker cable to the others cabinet to see if the speakers and cab made a differance.I believe the plastic covered hook up wire,the lead dress and the hotter trannys are all the blame. I tried a 5AR4 in place of the 5U4 and rebiased and still no luck.I have,to this day,never heard a silverface amp that sounded like a blackface even with all the tweeking.
     
  15. Blue Strat

    Blue Strat Member

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    Thanks John and Slider. I've been tempted to mount the tone stack "in the air" coming off the pots to eliminate the board from contention in, at least, this part of the circuit. I'll try adding an insulating layer.

    Silder, I agree in general, though I have encountered blackface amps that were inferior to even "some" silver face amps.
     

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