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. itsGiusto

    itsGiusto Tele-Holic

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    I'm still interested in buying a Twin Reverb - certainly the price is much lower to buy a master volume one post-1972 as opposed to a non-master volume one pre-1972. I'm quite comfortable making modifications to amps, so if all that's required to put it back to earlier specs is to detach the master volume pot, then I feel like I could do that easily and save $150 to $200. Possibly the only downside would be that I'd still have that MV pot there, but it won't do anything, which could annoy me, but is probably worth the money I'd save.

    Are there any other differences I should be aware of between early and mid-70s twin reverbs? Build quality, transformer quality, sloppiness of wiring, other circuit changes, PCB vs eyelet board, etc?
     
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  2. G.Rotten

    G.Rotten Friend of Leo's

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    I haven't anything useful to say in regards to your question, I only have my own question.

    Why is there so much hate for the master volume? I like my 75 TR. I consider its master volume to be a good thing.
     
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  3. adjason

    adjason Poster Extraordinaire Silver Supporter

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    I've owned three -I actually like the master volume on a twin- I use it and don't see it as a negative-great amps as long as you don't have to move them-keep your eyes on craigslist- these pop up in the $600-$700 range as nobody seems to want them these days
     
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  4. itsGiusto

    itsGiusto Tele-Holic

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    Haha, yeah, it's a good point. I think that people like the idea of the vintage golden age of blackface Fender, and the MV takes the amp further away from that. It's true that with the MV turned all the way up, it doesn't impact that tone that much. For me, I think I just like the idea of having the completely original, iconic circuit of the 1965 TR, and want to mod the amp so I can get it to those specs.
     
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  5. G.Rotten

    G.Rotten Friend of Leo's

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    I once knew a guy with a Fiero that put on the Ferrari body package & Hot Rodded it, but it still wasn't a Ferrari.

    It was still kind of a cool car though.

    You could save a couple hundred bucks turning something into something else, but in this case you'll just have a modified mid 70's TR.

    It's still kind of a cool amp though.
     
    Last edited: Dec 24, 2020
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  6. itsGiusto

    itsGiusto Tele-Holic

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    Haha, yeah that's a good point, but there is some difference in the analogy. For the car, I'm sure there are tons of mechanical differences under the hood, and probably the outside wouldn't look the same either. But for an amp, if you ask me, it doesn't matter to me when it was actually made, it matters if it was made to the same specs. An amp which was made in 1965 should sound the same as one which was made later but then modified to the exact same specs (barring differences in component quality). I'm after the sound, not the actual date of manufacture.
     
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  7. G.Rotten

    G.Rotten Friend of Leo's

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    Fair enough. The alternate message was, spend the other $200 & get what you really want.
     
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  8. itsGiusto

    itsGiusto Tele-Holic

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    Ah, maybe. But what I really want is a 1965 blackface twin reverb. But I'm certainly not willing to spend the extra $1000-$2000 to get that! The hype on those has raised them to ridiculous prices! And from what I understand, the SF ones are basically just as good, and basically the same circuit.
     
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  9. J. Bonkosky

    J. Bonkosky Tele-Holic

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    Just get a earlier non master volume SF twin reverb. They should be as cheap as the my one. There are circuit differences between the BF and SF variants. But those changes range from almost none to many that may or may not make a sound difference depending on the circuit you get. The wiring is a bit more sloppy on the SF amps but not the worst. Printed circuit boards didn’t come until the mid-late 80s. You could pick up a reissue BFTR used for a nice price and have the tone you want with no hassle. Good luck.
     
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  10. itsGiusto

    itsGiusto Tele-Holic

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    Thanks! I'm not willing to get the reissue because another thing that's important to me is to have an original board, not a PCB - I really dislike PCBs for various reasons, including maintainability. I've had too many bad experiences with PCBs.

    And from all my searching, I don't think that the non-MV twin reverbs are as cheap as the MV ones anymore. I think that that probably was the case a few years ago, but I no longer see it. I'm unable to get a non-MV one for less than 800 (if it's in fair condition with replaced speakers). Whereas I can get an MV-one with original speakers for 650-ish.
     
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  11. davidge1

    davidge1 Friend of Leo's

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    If you don't like the master volume on the amp, just don't use it. Just having it there couldn't affect the sound of the amp... could it?
     
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  12. Jowes_84

    Jowes_84 Tele-Meister

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    Hi

    imo, the late 70’s Twins-great for the money. I picked up a Vibrosonic Reverb on classifieds for less than 700 ... and that in Germany, old Fender stuff is generally quite a bit more expensive here. It still needs a bit of work but is playable and sounds good.

    I don’t think the MV makes them a bad amp. It can be a good thing.

    If you have the money, buy a BF AB763 amp... if not this is a great, affordable alternative

    to the initial question:
    Besides smaller stuff here and there, the later Silverfaces had quite a different Phase inverter circuit.
    Also, the boost circuit is funky and I don’t like it. But, no one is forcing me to use it so it’s fine with me.
    I started a thread about my Vibrosonic Reverb (which is a Twin with 15” spk) and never got around finishing it-hopefully I can finish over the holidays.
    schematic for reference below

    The wiring looks messy but all in all the quality is good, it is hand wired and easy to repair/mod

    so my suggestion is to get a late SF Twin (not the 135 Watts version though) and modify it if you feel you have to

    there are many sources out there for modifications and so called black facing - really not an up to date term anymore - but that’s what they call it.

    The ultrlinear amps with 135 Watts are a whole different thing - I don’t know anything about them.

    Merry Christmas !
    upload_2020-12-24_21-8-58.jpeg
     
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  13. itsGiusto

    itsGiusto Tele-Holic

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    It can, but probably not much. I haven't looked that in-depth to how it's implemented specifically in a TR, but having an extra resistor to ground can bleed more high frequencies to ground. Again, it may not matter too much depending on how it's implemented in this amp but sometimes it can matter, like for example, if you change the volume pot on a strat from 250k to 500k, it can sound too bright, and vice versa if you change the volume pot on a Les Paul from 500k to 250k.
     
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  14. itsGiusto

    itsGiusto Tele-Holic

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    Oh, interesting, I was not aware of this! I'll have to look into the schematics in greater detail to see what the PI differences are!
     
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  15. J. Bonkosky

    J. Bonkosky Tele-Holic

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    You should also take into account that the original MV twin reverb speakers may not be anything you would want either. Also If you are willing to mod a MV or non MV SFTR then why would originality be of any concern?

     
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  16. schmee

    schmee Doctor of Teleocity Ad Free Member

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    Just watch out for the UL ones, they are MV.
    there seem to be a lot of 71 Twins out there non MV at good prices. Must have been a big year for Twin sales.
     
    Last edited: Dec 24, 2020
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  17. itsGiusto

    itsGiusto Tele-Holic

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    That's true, I just meant it as a point of comparison, evidence of why it seems to me that the MV ones cost less than the non-MV ones.

    For me, the original speakers don't matter that much. I figure I will likely end up replacing at least one of the speakers in whatever I get so it's more like a Jensen that would have come in a BF Twin Reverb, maybe a Weber Ceramic Chicago 12.
     
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  18. itsGiusto

    itsGiusto Tele-Holic

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    Cool, looking at these two schematics, it does look like the PIs have different values!
    http://ampwares.com/schematics/100W_Mast_Vol_SF_Twin_Rev.pdf
    http://ampwares.com/schematics/twin_reverb_ab763.pdf

    I'm not sure what all of the differences would do, but it seems that the plate resistors are significantly lower valued in the SF, resulting in higher voltage going to the plates, ~320 vs ~245 in the BF one. I imagine this would result in it being louder, and having more headroom before distortion in the SF circuit as opposed to BF. This could also be something good for me to change back to BF specs.
     
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  19. Chiogtr4x

    Chiogtr4x Doctor of Teleocity

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    I forget, how do you work a Master Volume Fender ( Twin or other) so that it operates like and older BF/SF?

    Do you just crank the MV knob all the way, leave it there, and then just work the Volume control as usual?

    Or the opposite? ( crank Volume, then use the MV for volume)
    Thanks
     
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  20. J. Bonkosky

    J. Bonkosky Tele-Holic

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    Just crank the master and use the Channel volume. But the cool thing is you have options and you can make the MV sound very good at low volume. Not that a black face one sounds bat at low volume either. But you get my point.
     
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