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Mid-70s Twin Reverb vs Early-70s - Is the MV the only difference?

Discussion in 'Amp Central Station' started by itsGiusto, Dec 24, 2020.

  1. Milspec

    Milspec Poster Extraordinaire

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  2. BobbyZ

    BobbyZ Doctor of Teleocity

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    Someone once said you can tell the Twin Reverbs that sounded bad by their condition. Those will be the ones in nice shape. :)
    I've played enough silverfaces to think that's true! They don't all sound the same, some stay clean all the way up to insanity volume. Those suck in my opinion.
    Try before you buy if possible.
     
  3. Wally

    Wally Telefied Ad Free Member

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    I have to ask for clarification I have no idea what ‘pre-PI moped buildup’ is. The larger caps passes lower freqs than does the smaller cap as I understand it. Given all else equal, this yields a warmer sonic. I have changed those .001mfds out to .01mfd just for this reason.
     
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  4. Paul G.

    Paul G. Friend of Leo's

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    On the one hand, the earlier you go, the better the build quality and some components are.

    On the other hand, I think the silverface twins, even the later ones, sound very, very nice and are serviceable and reliable.
     
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  5. BobbyZ

    BobbyZ Doctor of Teleocity

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    Well with early silverface you've got the much maligned brown coupling caps. Not sure if their
    reputation is deserved or just based on their resemblance to something the dog leaves on the floor. :)
    I avoid early silverfaces because it takes a new power transformer to get the voltages right. I know the numbers on the schematics are the same but if you compare the ab763 with the aa769 and aa270, you'll see they changed to a lower voltage PT without a center tapped filament winding. You can't "blackface" that away.
     
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  6. Wally

    Wally Telefied Ad Free Member

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    Another reason in addition to the cab why I might like a late ‘60s TR.
     
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  7. itsGiusto

    itsGiusto Tele-Holic

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    Very interesting. You said that you avoid the "early silverfaces". Are you saying that they later changed back to the correct voltages, meaning later silverfaces are better? What year did they change to lower voltage PT, and when did they switch back?
     
  8. Ringo

    Ringo Poster Extraordinaire

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    I've owned several Twin Reverbs over the years, a 69, mid 70s and later 70s, had one that was modded to run only a pair of EL34s , it was still loud and still sounded like a Twin Reverb - to me!

    To me they all sounded great. There is a LOT of negativity about the later 135 watt UL MV Twins.
    I had one and used it for many years, IMO it was a great sounding amp. If you want gain tones you'll need an OD or Distortion pedal but that's true for any Twin IME.

    Sometime in the mid 70s Fender CBS starting building the cabinets with a glued in speaker baffle, and removeable grill cloth frame.
    Earlier SF Twins IIRC are non master 100 watt and have the removeable baffle.

    Sometime in the later 70s the Twin amps were up to 135 watt , Ultra linear transformers, and master volume. The cabinets are heavier.

    If you can play through any Twin Reverb that you are thinking about buying, if you like it that's ultimately all that really matters.
     
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  9. Wally

    Wally Telefied Ad Free Member

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    The change to the glued in baffleboard occurred in late 1970/early 1971. This is a major change for my tastes....as I noted earlier. The UL Fenders had bigger transformers....500VDc and the UL demanded that.
     
  10. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    A master volume make an amplifier 1,000 times more useful, but it also steers away from the original design so it must be baaaaaddddd.... because heaven forbid someone does something innovative to a guitar product.
     
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  11. G.Rotten

    G.Rotten Tele-Afflicted

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    6 saddle bridge. Let's see how that flies!!!
     
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  12. BobbyZ

    BobbyZ Doctor of Teleocity

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    You'd almost have to measure it to find out because there's a whole lot of SFTR schematics unaccounted for. The only one I've seen for a master volume SFTR is a later one with the pull boost. Never seen one for the non pull boost or the later 100 watters with the hum balance pot.
    Of the available ones on say the Fender Amp Field Guide, only the one for a MV PB has the same plate voltage as a blackface.
    When I first started out shocking myself I read an article somewhere about the low voltage SFTRs. I was messing with a SFTR then and swapped in a blackface power transformer. That changed the amp for the better. Before it stayed clean all the way up with humbuckers.
    I'm not recommending replacing the PT Willy nilly here. But if you've got an SFTR and it just ain't quite right to your ear, you've done everything else and it's a low voltage one, that might be it.
    Just looking at schematics again. The AB763 shows a 340v-340v PT with 460v on the plates.
    The aa769 shows 315v-315v with 405v on the plates.

    If I had one of those 315v-315v PTs handy I'd build a 5F8-A with it. Then use a separate 5v transformer for a 5u4, that'd likely get the voltage about right in that application. Originally they used a 300v-300v with a GZ34. Or skip the 5v thing and use a Weber Copper Cap.
     
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  13. itsGiusto

    itsGiusto Tele-Holic

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    If the SFTR PT is lower in voltage, and you swapped in the BFTR one which is higher in voltage, wouldn't it have more headroom, not less? I thought that higher B+ means more headroom and less breakup as you go up in volume.
     
  14. BobbyZ

    BobbyZ Doctor of Teleocity

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    Yeah it's weird that way. :)
    The higher voltage just works in that circuit.
     
  15. Ringo

    Ringo Poster Extraordinaire

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    OK I wasn't sure exactly when the glued in baffle deal started , thought it was later than that, maybe it was for some of the other models?
    My buddy has a 73 Super Reverb and it has a glued in baffle, we had to repair it , actually changed it out because the amp had been dropped, cracked one side of the cabinet and broke the baffle.
    I had a baffle from a Super Six that we cut down and put in his amp.
     
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  16. BobbyZ

    BobbyZ Doctor of Teleocity

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    I don't get too hung up on that "floating baffle" thing, it's a fairly thick piece of sawdust and glue board. Start talking tweeds with a thin piece of plywood and yeah there's some resonance there. But that stiff stuff in a blackface or a silverface? Cross connecting between black and silverface Twin Reverbs and Super Reverbs I can't tell any difference from floating to the glued in style.
    Sure I prefer a BF style cab, it's just nicer, but I'm not going to pay more for that cab with a 1968 circuit full of dog turd caps, just to get a "better" cab.
     
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  17. Wally

    Wally Telefied Ad Free Member

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    For my money the difference is the separate grille board....they buzz, rattle, and deteriorate....looking really shabby before they fall off in pieces. There are a few extra pounds there, too.
     
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  18. Wally

    Wally Telefied Ad Free Member

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    And...I have never been unable to make a late ‘60s SFTR sound good.
     
  19. Ringo

    Ringo Poster Extraordinaire

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    I guess everyone has a different opinion of what sounds good, I've owned quite a few later SF Fender amps, Twins and Super Reverbs, they all sounded good to me, sometimes better than the earlier SF and even BF models.
    Especially on the early SF models there wasn't that much difference in the circuit.
    Before the internet told us otherwise I think a lot of people were perfectly happy with their SF Fender amps and CBS era guitars.
    Ignorance is bliss?
     
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  20. BobbyZ

    BobbyZ Doctor of Teleocity

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    Could be that low voltage?
     
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