Fender Super Tweed Build

Discussion in 'The Squawk Box' started by Cjsinla, Sep 23, 2017.

  1. Cjsinla

    Cjsinla Premium Member

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    Found it. It was a 1.5k and I do need it. So, they got all the resistors right in the order with none missing and none left over.
     
  2. Leña_Costoso

    Leña_Costoso Senior Member

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    Keep in mind the solid state rectifier may..... get those 450v rated caps very close blue smoke city.

    The schematic says 415v on the first cap. Keep in mind that was using the "50's Fender transformer" and modern ones tend to be a little higher. Keep in mind that they took an intern (they called it a summer job back then!) and gave him a VTVM and said here, measure and write down all the voltages on the drawings. They did so at whatever the voltage that day was at the factory. I know this because I met one of those guys about 20 years ago, and we had fun talking about how they did things (very sloppy but they seemed to get the job done!). And keep in mind the solid state rectifier will give you higher voltages than a tube rectifier, maybe 20v more B+. So, take a wall voltage of 114v (typical then) and make that into 415v. Then bump the 114v to 122v which is typical now. Add the SS recto and you're ... pretty gosh dang close to blue smoke time on a 450v rated cap.
     
    Last edited: Sep 23, 2017
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  3. Cjsinla

    Cjsinla Premium Member

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    I assume you saw that copper thing in the pics. They sent that, I thought that it was in addition to the tube rectifier but it was in place of. I ordered a tube rectifier last night.

    Does this look like a star ground to you guys?

    IMG_1439.JPG
     
  4. Cjsinla

    Cjsinla Premium Member

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    Questions re: power tube wiring. Weber and Mojotone reverse the blue and brown OT wires. Does that mean that it does not matter if I switch the wires that go to terminal 6 from the board?

    Also, what is the advantage of linking terminals 1 and 8? They are linked on the Mojotone diagram but not on Weber's.
    IMG_0584.PNG
    IMG_0585.PNG
     
  5. eslover

    eslover Senior Member

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    Go weber (brown, blue) if you are a lefty guitar player, go Mojotone (blue,brown) if you're a righty. I always attach a 1 ohm to ground through pins 1 and 8 on each tube for biasing, so I can't say.
     
  6. Cjsinla

    Cjsinla Premium Member

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    Very funny, I'm a righty. This amp does not require biasing but I will probably tie the terminals together and ground them like Mojo suggests.
     
  7. Leña_Costoso

    Leña_Costoso Senior Member

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    No bias? Magic cathodes!
     
  8. Splattle101

    Splattle101 V.I.P. Member

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    It looks to me that you have the 100 uF cap for your bias supply fitted back to front in this pic.

    It's the cap on the extreme left hand end of the board. It is meant to be connected in reverse polarity. Have another look at your layout diagrams and check it.
     
  9. Cjsinla

    Cjsinla Premium Member

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    Wow, good catch. I didn't notice that cap was reversed on the diagram. I'll change it.
     
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  10. Cjsinla

    Cjsinla Premium Member

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    I mean that the bias is fixed on this amp, right?
     
  11. Axis39

    Axis39 Senior Member

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    What happens is, you hook turn the amp on and get an instant whine... then you reverse these wires. IT doe smatter, but without testing the OT, you'll never know. It's not important... But, leave the wires long enough that once you do turn the amp on, you can reverse them if you need to.

    I recently rebuilt a vintage amp... I had to gut it as it had been modded beyond all recognition (okay, so maybe that's an exaggeration, it had gone from 5f8-a to aa270 minus trem). When I turned it on, I got the instant whine... I hadn't changed these wires. Took me a minute to power down, drain the caps and reverse these two wires an voila!
     
  12. Splattle101

    Splattle101 V.I.P. Member

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    This amp is fixed bias. That means there's a fixed negative DC voltage applied to the control grids of the power tubes. That's the bias voltage. In modern amps that bias circuit has a little potentiometer in it so you can adjust the bias voltage. Thus they're 'adjustable fixed bias'.

    The original Fender 5F4 Super didn't have a bias adjustment pot, so it was just fixed bias. I don't know whether the Weber kit includes a bias adjustment pot.
     
  13. Cjsinla

    Cjsinla Premium Member

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    Good to know.
     
  14. Leña_Costoso

    Leña_Costoso Senior Member

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    Hey thought I'd chime here for a few.

    "The instant whine", which is a sound once heard, you will NEVER forget and will always know just what's up. Here's how it works. Your "extension" speaker jack is wired through a 56k resistor to form a negative feedback to gain stage (so called "recovery stage") just prior to the phase inverter. On later series amps, more modern designs (aka those with long tail pair phase inverter) the insertion of negative feedback is done slightly differently, but the idea is the same: For negative feedback to put the kibosh on the signal to smooth it out a bit, make it less ragged.

    You "could" reverse the wires on the tube sockets.
    OR just reverse the black and green on the speaker jack. Either will do.

    You might want to include a bleed down resistor on the B+, which is easy to do. Different values are suggested by different folks, but I use a 1m to ground to minimally impact the voltages

    And, you also may wish to add a little front support for the power transformer. EVERBILT 527 580 3/4 inch corner bracket works perfectly. Available at Home Depot. You will need to cut/file off one corner of the bracket slightly, so it clears the bell of the PT. On MY chassis, no fiddling was needed, and it all matched up perfectly without having to shim anything between the bracket and underside of the cabinet, nor did I need to elongate the hole in the bracket to allow it to "slide down" a bit in order to have clearance. You have a Weber chassis... YMMV, but adding the support is a REALLY good idea if you plan to transport the amp (aka "play out"). All original tweed Super, Pro, Bandmaster and Bassman amps had the "third screw" for that support - for a reason.

    Hope your build is coming along nicely!
     
  15. Cjsinla

    Cjsinla Premium Member

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    I hit a snag, the color of the wires from the PT don't match the diagrams. There is only one black wire and there is an extra brown one and a blue one. There's also a label on the black wire that says, "China." I'm starting to see why the Weber kits are the most affordable. I dropped a line to Weber asking about the colors, nothing came with the transformer that tells what is what. I'm seriously thinking about buying a Mercury PT but I think I'll wait to see how the Weber PT works first. In the meantime I plan to go to my local electronics parts store tomorrow to see if they have the right filter caps.
     
  16. Splattle101

    Splattle101 V.I.P. Member

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    The Weber trannies are not in the same class as Mercury, but they should do the job ok. If that's their standard 6L6 power tranny, it may have two high voltage secondaries. One will be lower voltage and that would be the one to use for your amp (if it is that tranny).
     
  17. Leña_Costoso

    Leña_Costoso Senior Member

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    Off the top of my head black brown and blue sound like a 240-volt primary
     
  18. Cjsinla

    Cjsinla Premium Member

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    You guys are on the right track, Weber got back to me. The blue is for the higher, modern voltages and the brown is old school.
     
  19. Leña_Costoso

    Leña_Costoso Senior Member

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  20. Cjsinla

    Cjsinla Premium Member

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    Coming along nicely, waiting to solder the filter caps.

    image.jpg
     

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