SFTR - Any Mods for Better Jazz Tone?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Washburnmemphis, Jan 23, 2008.


  1. Washburnmemphis

    Washburnmemphis Member

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    I have a Silverface Twin Reverb that I plan to replace the 100k plate resistors in to get rid of some intermittent static/"bacon frying" noise. I was wondering if there are any recommended mods that I could do while I'm in there, to make a very good amp better?

    AA270 circuit

    By jazz tone I'm thinking Pass/Montgomery/Burrell rather than Stern/Metheny.

    Currently everything is stock except for replacing the electrolytic caps and converting the bias balance to bias control.

    I want to keep the cleans as clean as possible so I assume "blackfacing" it isn't the answer.

    The amp is set up with two Weber Michigan speakers and currently TAD 6L6WGC STR tubes.

    Any suggestions, tips, etc are appreciated.
     
  2. AL30

    AL30 Member

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    Well Blackfacing it will help take the "spike" out of the high end and mellow things out a bit. But, if you don't want to go that route - Have you tried a 12AT7 in the V1 or V2 (not sure which channel you're using) position? And are you running a 12AT7 in the PI spot? Some people swap this for a 12AX7 for more gain.


    AL
     
  3. Blue Strat

    Blue Strat Member

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    Since many find this the perfect jazz amp (Wes Montgomery for one) this begs the question: "What do you feel the amp lacks for your needs?".
     
  4. Washburnmemphis

    Washburnmemphis Member

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    Nothing lacking, just curious if there is any fine tuning that can be done to make a great amp even better.

    For example, the amp sounded good with the stock Fender speakers but now sounds much better with the Weber Michigans.

    I was under the impression that Blackfacing would lead to less headroom, but maybe I will look into selectively Blackfacing certain parts of the circuit.

    re: the tube changes, Thanks for the tip, I 've tried different brands but I hadn't tried different types.
     
  5. AL30

    AL30 Member

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    If it's headroom you're after then you may want to leave it "as-is". However, headroom on any twin isn't that much of issue. How loud are you playing this guy? Unless you over-ride the Master Volume (not sure if your twin has one or not) you probably won't get much of a break-up until around 5 or 6 - and that'll get the cops called on you in no time. :)

    AL
     
  6. Clutch21286

    Clutch21286 Member

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    I would not blackface to get a jazz tone. JMHO.

    I also read that a 12AT7 is not a good tube for anything other then phase inverter. I would suggest speakers or tubes (12AU7 or 12AY7) to get what your after.

    FWIW - I would check with Blue Strat regarding the 12AT7.
     
  7. AL30

    AL30 Member

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    Not trying to be negative but have you tried it? Where did you read this? I'm sure some players don't like it - I'm not one of them. For certain amps I really prefer a 12AT7 in certain slots. It seems to "warm" things up a bit while lowering the gain. All amps and ears are different.

    I agree with checking with Blue Strat on the tubes.

    AL
     
  8. Blue Strat

    Blue Strat Member

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    "Better" can mean 4 different things to 4 different people. Unless you're specific all your going to get is opinions based on guessing what you like.
     
  9. Blue Strat

    Blue Strat Member

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    Then again, many of the tones that we emulate or our jazz heros emulated came from underpowered, dirty tube amps, not 80 watt clean amps.

    There's no single answer to any of this.
     
  10. Rosewood

    Rosewood Member

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    Boy that's true, some of those old recordings you could hear the amp running out of headroom Quick. Then came the Polytone.;)
     
  11. Washburnmemphis

    Washburnmemphis Member

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    Yes and I welcome differing opinions, I don't plan to make any changes that aren't readily reversable.

    Sounds like the best approach is to continue experimenting with tubes.

    Thanks for all the responses.
     
  12. PRNDL

    PRNDL Member

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    That noise is usually caused by a bad preamp tube or electrolytics.

    While you're in there, I'd recommend measuring all of the tube and power supply voltages and check the bias and matching of the output tubes.

    You could also measure resistance values and replace those that are way off. You can measure them in the circuit, but the readings are usually lower. If you find one that's way off, remove one lead to get an accurate measurement.

    Some recommend replacing the carbon comp resistors with metal film for lower noise, but this usually removes tone.
     
  13. slider313

    slider313 Silver Supporting Member

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    The first thing I would do is take out those TAD's and replace them with either SED's or the New Tung Sol 6L6GC STR's. I find these to be the best tubes for Fender amps. It's a matter of personal taste but I'm using the Tung Sols and find them warm with a nice transparent woody tone.
     
  14. Blue Strat

    Blue Strat Member

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    "That noise is usually caused by a bad preamp tube or electrolytics."

    Preamp tubes yes, electrolytics: not likely.

    Plate load resistors and tubes are first on the list. Then coupling or tone capacitors.

    Electrolytic problems are more associated with hum, lack of power and low end, or blowing fuses.
     
  15. jay42

    jay42 Member

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    Try some different types of 100K plate resistors. You'll be surprised by the Vishay-Dale MFs, 71-RN65D-F-100K at mouser. Carbon films would be 294-100K-RC. Try 5751's or 12ay7's for V1, V2, and V4. That will darken the tone a bit...I prefer it that way, ymmv. Install a couple beam blockers.
     
  16. Washburnmemphis

    Washburnmemphis Member

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    Thanks guys, this is the kind of info I was looking for.:AOK

    PRNDL, I will probably replace all the plate load resistors but I plan to also do what you suggest and measure the resistance values to see if any others have drifted. Thanks.
     
  17. Washburnmemphis

    Washburnmemphis Member

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    Slider313,

    I tried your tube suggestions replacing the TAD 6L6WGC STR. My findings were:

    Tung Sol 6L6GC STR -
    Very good tone, to my ears as far as Fender cleans go it was hard to say whether or not it was better than the TAD. Depending on the day, I might give one an 8/10 and the other an 8.5/10.

    Winged "C" (SED) 6L6GC[​IMG]
    Great tone lots of depth, IMO easily better than the TAD and the Tung Sol. A keeper.:dude

    Thanks for the tips
     
  18. MrChet

    MrChet Member

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    Be careful, you may be on the slippery slope to TAA and GAS (Tube Amp Addiction and Gear Aquisition Syndrome).

    Webers Michigan speakers are his take on EVs IIRC. I had a Traynor MK III, which is virtually the same circuit as a TR. I didn't like EV or Altecs for jazz tone. Too sharp transient response. EMI GB-12s, Celestion G12-65 and EMI Texas Heat actually pleased my ear more. So at the risk of causing damage to your wallet, speaker swapping may be in order. Alnicos can be good in fixed bias amps, something like a P12N Jensen. YMMV
     
  19. Groovey Records

    Groovey Records Member

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    Thought I'd clarify a couple of thinhgs about Wes's Sound if thats the vibe you'd like to feel in your tone WashburnMemphis

    First this was his amp. He used a stock Standel Custom 15.


    [​IMG]

    Later a model he colaborated on with Standels owner Bob Crooks The Standel Super Custom XV. The 1965 SS 70 watt version featured two channels. The Normal channel included: Volume, Treble, Bass.

    [​IMG]


    In the above photo of Wes he is shown playing through the Reverb/Vibrato channel which included: Volume, Treble, Bass, Contour (cut only), Reverb, Intensity and Speed.

    [​IMG]

    In know small way the JBL-Lansing 15" High Fidelity speaker contributed to Wes's sound and tone. Along with his thumb and its slight caloused wart nothing shaped Wes's SSound more then this Standel Amp and his own musical genius.

    [​IMG]

    [​IMG]

    Iactually bid on this amp it went from $1150 to $2700 in 30seconds and I missed it. I believe that price is still a bargain. There is no other amp in its class and quality.

    Take a look at this thread I started on the History of Standel and some of the players associated with their Amps.

    http://www.thegearpage.net/board/showthread.php?t=358788

    EnJoY ThE MuSiC
    GrooVey Records
     
  20. phsyconoodler

    phsyconoodler Member

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    A good mod for Fender amps to get some nice jazz tone is adding local negative feedback at the first preamp tube(reverb channel)
     

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