I'm blackfacing a SF Pro Reverb...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Slick51, Jul 27, 2005.

  1. Slick51

    Slick51 Colonel Curmudgeon Silver Supporting Member

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    starting from an AA1069 schematic currently.

    My question....

    Where do I end up, schematically? I'd like to go as close to the AB763 as possible while maintaining reliability(with a full electrolytic cap job as well as upgrading some of the coupling/tone caps, 5AR4 vs the 5U4GB rectifier, bias adj vs balance, clipping out the .002uf caps on the power tubes, 3 prong wiring correction/dropping the ground switch/cap, replacing the Utahs w/ JBL D120Fs, the whole nine yards).

    From the schematics, I think the AA165 is a suitable sub. And, since the voltage is lower, the Pro transformer should be fine.

    Is the difference in the tone that obvious? Is it worth the hassle... :p

    Like to hear your opinions...

    Slick51
     
  2. TheAmpNerd

    TheAmpNerd Member

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    Schematically, you'll end up at the AB763 or AA165
    if that is what you used.
    As long as you do the work correctly, use at least the
    min votatage rated components you will have a
    very reliabe amp.
    Which ever schematic you choose is fine, you've voltages will still be with in 20 percent.
    Well, if you are starting from a 1970ish amp that hasn't seen any service work performed on it, Hell yes, you are
    going to be amazed at the difference!

    Is it worth it? Depends on you. If you like the sound of old dried out caps, no dynamics, little sustain, snap crackle pop, and don't play very well and you want to hide your playing in the tone of a vintage amp with the reverb cranked up...I propbably wouldn't do it.

    HOWEVER

    If you want an amp that kicks ass, has good dynamics,
    touch sensitivity, sustain, and will help you hear how
    your playing really sounds, then do the following:

    electrolytics

    Do that first and see what it sounds like to you.
    This is also a good trouble shooting step.
    Make sure the amp works before you start
    doing anything else!

    THEN

    Once the amp has the fresh electrolytics and works
    properly, you can then judge what the rest of the circuit
    do in comparison to a properly working amp.

    ASLO

    Fresh electrolytics are one of the most bang for
    the buck service proceedures you can do. Less
    time consuming then desoldering and resoldering in
    lots of little components, (i.e., resistors, caps, wire).

    THEN

    You do the rest of the blackface changes one section/
    stage at a time and see what the changes do for you.


    SUMMARY

    Electrolytics first, play the amp for a while get comfrotable
    with it, learn its tone, ensure no problems.

    Then, make other changes as you desire.

    Learn from this and know that we are here to help.

    Have fun and enjoy!
     
  3. Slick51

    Slick51 Colonel Curmudgeon Silver Supporting Member

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    All good points! Thanks so much...

    Slick51
     
  4. TheAmpNerd

    TheAmpNerd Member

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    You will be surprised at the difference.

    Clip out those supressor caps on the
    outputs!
     
  5. doctorx

    doctorx Member

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    I have blackfaced several Fender amps and can say the difference is remarkable. The AB763 circuit is just damn cool.

    I replace all ceramics with silver micas, but some people like the tone of the ceramics.

    So far I have used Orange Drops, but people say good things about the Yellow Mallory caps.

    You can fool with the tone caps too. Try a 500pf instead of a 250pf, and visaversa. The .047 can be changed out for a .033 or .022, which is what the Super Reverb used. I like the .022, and I just put a .033 in a Bassman 100 I modded, looking forward to see what that is like.
     
  6. doctorx

    doctorx Member

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    I just looked at the AA1069 and saw it already has the .022 in the tone circuit. You could put a .047 in the normal channel for some variation.

    Try replacing the 6800 ohm resistor with a 8200 in the normal channel as done in the Bassman for more mids.

    If the amp has those turd brown caps replace them with Orange Drops or Mallorys. Those brown caps suck. If the amp has those dark blue chicklet caps, they are a little better but still not as good as ODs or Mallorys. What year is the amp?

    Modify the amp so you can have reverb and vibrato in both channels.

    Replace the Vibrato Intensity pot with one that has a switch so you can cut out the Vibrato circuit. I did this to my Bandmaster and it provided a noticible boatload of gain.

    This is a cool amp. Really, it's not much different from the Blackface amps to start with.
     
  7. Slick51

    Slick51 Colonel Curmudgeon Silver Supporting Member

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    I plan to replace all the 'turds', testing both Mallory 150s and 715P Orange Drops to see what I like better. I'm doing the channel equalization mod that Kevin O'Connor shows in his "The Ultimate Tone" to get the reverb/vibrato on both channels.

    I don't know where to get the vibrato pot w/ switch, but will find it.

    The amp is a '73, with the white Mallory cathode bypass caps, plus brown paper Mallorys in the filter cap positions.

    I have a well-stocked parts bin, and plan to try many configurations for the tone stack (and see if my ears follow my eyes, using the Tone Stack Modeler at Duncan Amps).

    I have many other amps, so this one is just a personal hobby shop; no rush. I just didn't want to base the whole set of mods on an unknown or a baseless assumption...

    Thanks everyone...still listening.

    Slick51
     
  8. TheAmpNerd

    TheAmpNerd Member

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    Hey Doc,

    Did you just blackface the amp or did you do the old lytics at
    the same time?

    It is cheating if you did more than one thing at a time
    and call the change remarkable.:BEER
     
  9. Slick51

    Slick51 Colonel Curmudgeon Silver Supporting Member

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    :confused:

    The good Dr is being helpful, and has not implied I bought an amp to hide my playing with...let him speak.

    Slick51
     
  10. doctorx

    doctorx Member

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    Of course I changed the electrolytics.

    I don't call it cheating when you replace low grade parts selected by bean counting accountants, and circuits designed by clueless post-Leo engineers with parts and circuits that reflect Leo's superior designs.

    And yes, to me the difference is remarkable. YMMV.
     
  11. TheAmpNerd

    TheAmpNerd Member

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    Slick, you misread what I said. Read it again carefully.

    For your own learning and education, if you do the
    steps as I've suggested, then my friend you will
    be enlightened.

    PS - From what I can tell the ProReverb never had
    a AA763 or AB763 circuit. The earliest is AA1065,
    which is close to the AB763 circuits.

    Doc

    It is misleading to say changing this amps circuit to
    blackface spec will be "remarkable" when in fact
    you are
    restifying -( borrowed muslce car term,
    changing and upgrading components)

    at the same time. AND gretting rid of some of the
    supression caps, etc.

    Separating the two; (i.e., restify and blackface)
    is essential.

    Consider the following:

    A. Changing all the electrolytics in an amp >20 years
    old will have a remarkable affect!


    B. Add to this, upgrading key coupling caps.

    C. Add to this upgrading key resistors.

    D. Add to this, fresh new or nos tube.

    E. Add to this good efficient speakers.


    Performing A - E on any amp will have a huge affect
    on its tone, playibilty, sustain, clarity, etc.

    Finally, if after all these changes (or only some)
    you then change the circuit slightly to use the blackface value of component, then you will find the change

    LESS

    remarkable.


    I'n not sorry if I burst anybodies bubble.

    I've restified BF and SF amps side by side
    kept the circuits as designated, then
    played them side by side.

    NOT MUCH DIFFERENCE between them.

    But a huge difference from whence they came!


    Slick,

    Restify it first. Listen then play. Then pitch in the
    extra cash for the 1/2 dozen or so resistors and
    perhaps a few caps.

    Stick them in the amp, you like anyone else will
    think the result is less than remarkable.

    HOWEVER

    Do everything at once an the result is remarkable.


    This is a subtle but very important point to grasp for
    anyone who tinkers with amps.
     
  12. Slick51

    Slick51 Colonel Curmudgeon Silver Supporting Member

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    [rant]

    First, off...no bubble bursting here. I suggest you read my initial mail as well.

    I said I'd remove the suppressor caps in my initial post, a point you've missed, twice.

    I've been soldering circuits since the early 70s, and repaired RADAR at the end of Vietnam; nothing marvelous about a tube circuit for an audio circuit, especially after seeing the tube radar on an early model F-4. And I fully understand the concept of stepwise repair/mod and evaluate. Are you a Weapons Control System mechanic? I don't know. The point is, you don't know me either. Don't assume the worst. And learn some tact.

    And, after looking at the schematics available on the net and in my library, I know there is very little to be gained, and the amp started with AA165, not AB763; but since it is already so close, an AB763 mod seems doable. I asked the population at large if my assumption is correct. You answered yes, which I appreciate, but then had to lecture me. I don't need that, and neither does this board.

    I have played for 40 years, and have owned many amps. I like tone, not bad caps.

    I don't hide my playing from anyone, and certainly not behind reverb. Ask someone that knows. I'm not Dick Dale.

    I have a well-stocked shop. Hundreds of dollars of parts (filter and tone caps, resistors (metal film, carbon comp and carbon film, cement power), thousands of dollars of tubes; two scopes, generator, VOMs, digital (2) and analog. 15 unmounted speakers to go with the 25 in various cabs. 19 amps, 30 guitars (which I also build). I've modded several amps. I repair my own amps, often with no schematics. I don't need to save my pennies to buy another resistor....you also missed that fact, above.

    I also have Kevin O'Connor's The Ultimate Tone, Aspen Pittman and Gerald weber's books, the Audio Cyclopedia, and even Torres' missive. And understand them. That's how I use my engineering degree (and meteorology, and MS in Atmospheric Chemistry..."Theory of Jovian Atmospheres" anyone? LOL)

    And even though you tell me how much better it'll sound (again, my question of 'is it worth the hassle?') the answer is yes, then no.

    I appreciate the fact you answered. Doc answered me too. He gave info and didn't assume he was the source of knowledge and no one else had a clue.

    Don't speak down to me. You don't know me.

    I thanked you even after the parental response you gave me.

    I'll thank you too to assume I'm your equal.

    [/rant]

    Slick51
     
  13. TheAmpNerd

    TheAmpNerd Member

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  14. hasserl

    hasserl Member

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    Hey Ben, sounds like a cool project. I picked up a SF Super Reverb not long ago. I originally planned on bf'ing it, but you know what, it sounds so damn good I'm not going to mess too much with it. But the circuit in my amp is pretty close to bf specs anyway, other than a MV and boost circuit (both of which wil probably be removed/modified) and some differences in the PI. I'll either completely remove the MV and possibly use the pot for something else, like a Soul control, or a Raw control, or make it a post PI MV. I haven't decided on that yet. And I have several other projects in front of this one anyway, so it'll be a while before I get to it. In the meantime I've already used it on a gig and everyone loved it.

    Keep in mind that the trem circuit robs a good deal of gain from the signal. I plan on setting up the Normal channel a bit hotter than the Vibrato channel, so I won't be adding rev or trem to it. Besides, I don't want either of those features with OD anyway. So the Normal channel will be my lead channel. Than with an AB pedal I can select either channel on the fly.

    Also, one of the things I found is there is a lot of sag with the 5U4 rectifier, too much for my tastes. But I'm not sure I want to go with a 5AR4 instead, because that will raise the voltages a bit and I'm not sure I want to do that. Fender changed the power trannies in the amps when they went to the 5U4 rectifiers, to compensate for the greater voltage drop. So a 5AR4 may give too high voltage. I'm considering having Weber build me a Copper Cap that will give me the voltage drop of the 5U4 but the sag characteristics of a 5AR4. I need to talk to Ted about that, but I think it will do the trick, give me the right voltage but without so much sag. It'll take a load of the PT at the same time.

    Anyway, let me know how your project turns out, and any interesting tidbits you find out on the way.

    Hasse
     
  15. hasserl

    hasserl Member

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    Dude, ease up. I don't think it's all that important to him to be able to say it sounds superb because it's blackfaced. I think he just wants a great sounding and reliable amp, regardless if that means exact to bf specs or not.

    And I don't think calling him a squid is helpfull either, even if it was in jest.
     
  16. Slick51

    Slick51 Colonel Curmudgeon Silver Supporting Member

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    And if I didn't know better, I'd say you were a jarhead! Finally, something I understand.

    For the record, I'm a Lt Col, USAF, but I know many squids and jarheads...love them all. Snake eaters too. (everyone else...he accused me of being Navy, and I replied 'spoken like a Marine'. And I love the Special Ops guys too, fraternally)

    Rich: all points I'd considered too. This one is a AA1069, with no MV. The point above was that the Pro Reverb circuitry starts at the AA165; I wasn't clear with that. As my youngest (16) son says, (and I despise), 'My Bad'. Sheesh.

    I plan to go to the AB763, which really entails redoing the bias circuitry to get a bias adjust vs. a balance, clipping the snubbers out of the 6L6 circuit, changing a couple of caps, then tuning to taste. I'll do that after the cap job. I always test after changing one variable...

    I also will put a pot on the vibrato with an on-off switch, as Doc mentioned. Finally, I'll probably take a page from you, Rich, from the Hasserl mods, and put a NFB adjustment where I remove the ground switch/death cap. Or any mods I find later. I won't drill the amp, but I'll rotate a Post PI MV, or mid eq, or NFB, or fat switch, or speaker phase (to match to my Matchless DC-30), or whatever, through that location.

    This one is going to be a clean only amp, so the ch equalization will do fine. If I don't like it, I clip one wire, resolder one connection and it's back to normal.

    I also wholeheartedly agree that the cap job will be the biggest improvement. However, I have a pair of Weber reconed JBL D120Fs to drop in it, along with silver mica and polypro cap upgrades, new grid stoppers and screen resistors, new plate resistors, lead dress, etc.

    The AB763 conversion is so I can drop the upgrade details into casual conversations with flyboys and nerds!

    As you were; I'll be in the area all day...

    Slick51



    BTW, I found the 3 prong convenience plug for the back panel at Allied Electronics for $15, not the $25 as Metro charges.
     
  17. TheAmpNerd

    TheAmpNerd Member

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    Ya know Slick..

    ...I was going to tell ya a story, but I don't have
    time at the moment. I've got to go down to the
    cops place and get my side arm...was stolen
    20 years ago.

    The good thing is they tracked me down
    instead of just destroying it. They were
    concerned that it wasn't in the holster any more.

    When I get back I'll share the Jarhead Flyboy story
    with ya.
     
  18. Slick51

    Slick51 Colonel Curmudgeon Silver Supporting Member

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    You got it back after 20 yrs? Heck, that's a good story by itself! Congrats.

    Later
    Slick51
     
  19. TheAmpNerd

    TheAmpNerd Member

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    Oh boy, that is going to be special, I'll have to give it a
    few more "months"...the plot sickens...NRA., help!


    Let me open, saying not that there has been an interservice
    rivalry....

    After 9-11, this 55 year old retired Marine goes down to the
    recruiter office and tell the man that he wants to re up.

    The recruiters laugh and tell the old Marine, "you are
    too old, go back home". The old Marine, tells them, "I have friend in the pentagon"...

    The old Marine does, and the folks at the pentagon laugh and tell the old Marine, "you're too old, go home."

    "I don't think so" the old Marine says. And goes to that
    beach place in NJ and gets supplies, a row boat and
    starts out rowing to Iraq.

    A few days out, St. Peter sees the old Marine rowing to
    Iraq and tells God, "Hey God, this old Marine is rowing
    to Iraq, what shall I do?"

    God, looks at St. Peter and says, "Take his brain away,
    that will stop him."

    St. Peter does, and a few days later spies the old Marine
    again, still rowing to Iraq. "Hey God", St. Peter says,
    "that Marine is still at it, what do you want me to do?"

    God, looks at St. Peter and says, "Take his heart away,
    that will stop him."

    St. Peter does, and another day day laterhe sees the old Marine, still rowing to Iraq. "Hey God", St. Peter says,
    "the old Marine is still rowing, what do you think I should
    do this time?"

    God leans over and whispers into St. Peters ear.

    The next day after St. Peter did God's order,
    the old Marine rows in circles, for a bit, then
    finally he heads back to the NJ shore....

    ....there he is,
    rowing,
    without any balls,
    singing

    "Off we go, into the Wild Blue Yonder.... :dude


    Couldn't hep myself on that one.

    On a side note, I sent a pm, regarding a decal.
     
  20. Slick51

    Slick51 Colonel Curmudgeon Silver Supporting Member

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    And a Marine singing within a joke so OLD, it has dinosaur **** caked around the edges, true to form! LOL...

    AND

    The next time you need Close Air Support, call one of your beloved Harriers to perform the fratricide ;)

    PLUS

    Some thing never change.

    I'll get to the PM.

    A pleasure to hear from a brother-in-arms, no matter HOW old!
    Slick51
     

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