Fender Super Tweed Build

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

  1. Leña_Costoso

    Leña_Costoso Senior Member

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    Ozone? Oh hell no, it smells like bourbon! Wild Turkey 101 to be exact :p

    Seriously, no smell off the transformer or other stuff.

    I've never had an issue with Hammond transformer. They're build like shick brit house!
     
  2. Cjsinla

    Cjsinla Premium Member

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    @Leña_Costoso @Splattle101
    Ok, still having trouble with my digital meters, including the one that Leña sent me. House voltage reads at 165 but when the electrician came recently his meter reads at about 122. Digital meter says plate voltage is over 600, that can’t be right.

    My old analog meter has a needle on a scale that tops out at 250 DC. When I put the selector on 250V, it pegs the needle. When I put the selector on 500V, the needle goes to 200, maybe just a hair over that. I assume it’s X2, so about 405 VDC for the plate voltage. This same meter reads my house AC at about 120.

    Splattle may be right about the B+ voltage on Mercury transformers. BTW, Patrick at Mercury told me about transformers having to break in again. His exact words were, “most people don’t know about that.“. Hmmmmm

    image.jpg
     
    Last edited: Dec 2, 2017
  3. Leña_Costoso

    Leña_Costoso Senior Member

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    Well, hey... it was a freebee that we paid about (literally) two bucks for, with a battery! We got like 100 of 'em outta China, gave 'em away for a class, and about 30 were leftover for about fifteen years, until I pulled the batteries out last year. However.... there are a few more where that came from :rolleyes: Not many, but a few.

    Merry Christmas!

    Well... the turns ratio cannot change. That means the impedance ratio cannot change. It also means the voltage ratio cannot change. Those items are a matter of primary vs secondary winding count. The DC resistance cannot change, as that's a function of length of wire and wire diameter. The magnetic field cannot change, as that's a function of the primary and the iron. The inter-winding capacitance can change, emphasis on "can" because I have no idea if it will. That is a function of the tightness of the windings and interleave. Interleave is fixed, so maybe... maybe.... the coating on the wire is still shrinking in after baking? We don't get transformers near hot enough to change the varnish, so maybe its residual from the manufacturing process and playing (getting it "warm") helps gas out the winding varnish, making a very slightly tighter winding, which should... have higher capacitance. Dunno if that makes any diff in the tone on a PT. OT perhaps, but PT? Unsure on that.

    If you can hold out till Wed or Thurs I'll toss another two bit meter your way.
     
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  4. Leña_Costoso

    Leña_Costoso Senior Member

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    Thinking more on it, I looked into transformers a while ago, 20 years ago or so. Knew a guy in Tx that I met online, who knew a whole lot about transformer design and especially single ended transformers. He was in the industrial transformer biz, but an audiophile. Never touched a guitar amp tho.

    There are things, items of factoid lore, that are not supported by any sort of measurable data. All I know is that red playing cards get me about 1/2 mph faster vs the black ones on the spokes of my bike!
    [​IMG]
    (Shown before speed enhancing, female attracting, go fast cards added to spokes)
     
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  5. Cjsinla

    Cjsinla Premium Member

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    Very funny. BTW, I was trying out the Super at volume and it started to develop a sound like static at idle. I tapped on all the tubes and heard nothing out of the ordinary. Bumping the chassis with my chord or tapping the back of the cab caused the amp to emit a single tone with nothing plugged to he input. I rotated v2 and v3 with a spare 12ax7 I had but no change. Taking the 12at7 out of v1 and putting in an ecc83 caused loud static and the tone. Is it possible that one of my power tubes are bad?

    Just plugged into the tweed Deluxe, it’s doing the same thing. Plugging and unplugging from the input jacks makes the problem worse on both amps, static and a ‘tone’. Is this a characteristic of tweed amp circuits?
    @Leña_Costoso
     
    Last edited: Dec 2, 2017
  6. Leña_Costoso

    Leña_Costoso Senior Member

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    That's hard to diagnose. I always like to make sure that the little spring switch in the input jacks is making great contact. That's a common source of noise when there's nothing plugged into the amp. You can also take out the two right hand preamp tubes and the super. See what that does. Then install the middle preamp tube. Evaluate again. Finally the right hand preamp tube.

    Both amplifiers doing it make it more than usual. I wonder if there's some sort of General interference occurring had you a locale.

    I just had a great test for myself. Turn on my amp and crank up the ham radio just to see what happens!
     
    Last edited: Dec 3, 2017
  7. Leña_Costoso

    Leña_Costoso Senior Member

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    Should have asked what that tone sounds like. Hum? Squeal?
     
  8. Cjsinla

    Cjsinla Premium Member

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    Tracked down the issue. It’s all related to the normal volume circuit. No hum, static or squeal when normal volume is at zero. Bright channel can be turned up to 12 and it’s whisper quiet. Plug a guitar in and everything is great. Plug into the normal channel, turn up and the problems start. Problem is the same with two new 12at7’s. Pin 2 makes a hissing sound that gets louder as I approach it with a chopstick. Tapping that pin makes a metallic sound with both tubes. I had two wires grounded to the back of the normal pot but I grounded them elsewhere and the problem remains.

    It might be a bad socket. I think that I put a tube into that socket prior to soldering wires to it and one of the pins pulled out when I removed the tube.

    @Leña_Costoso I’ll have to check the springs on the jacks on the normal channel.
     
  9. Leña_Costoso

    Leña_Costoso Senior Member

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    Make sure the power supply is drained down. You can use a small instrument to tighten the clip inside the socket. That could very well correct your socket issue.
     
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  10. Cjsinla

    Cjsinla Premium Member

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    You are a genius. It was the #1 jack on the normal channel.
     
  11. Leña_Costoso

    Leña_Costoso Senior Member

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    Lucky guess.
     
  12. Cjsinla

    Cjsinla Premium Member

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    I’m thinking that the Deluxe may have a similar problem. It’s been having similar symptoms.
     
  13. Leña_Costoso

    Leña_Costoso Senior Member

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    Could be so!

    I've had my share of trouble with those things to the point that I wire ground every sleeve. I don't know if Switchcraft is slippin' or if they're warping under heat of soldering. My own recent Super 5F4 had two of 'em. One of each channel, of course!

    That sort of "let's have a lookey at them thar pesky varmints*" should be part of any amps shakedown cruise.

    Another thing that gets 'em is minor corrosion. Here in Fl, we run windows open from October to April, so there can be humidity related issues. To clean those switches, you gotta be real careful, but its easy. I cut a little strip of heavy paper, like index card paper, or even heavy envelope paper. Only need a little width and a strip long enough to pass thru the contact area. Gently pull back the "tip" so it breaks free of the spring leaf switch. Put the strip in between. Let the tip return to its regular position, and pull the paper out. There's just enough tension there for the paper to burnish the contacts. Once you do that... they generally stay good for a very long time (years and years).

    Things I can remember doing -
    Checking the springy switch leaves on the input jacks
    Checking socket pins for tightness
    Checking the springy switch leave on the output socket
    Making sure nothin' ain't gonna touch on the standby switch, on off switch.
    Make sure I got no wires layin on something likely to get nice and toasty
    Check the welds on the chassis (before beginning, sorry Mr Ted Weber, Sr, but your welds sucked when you was yet alive, and now I'm gun shy).
    Triple check orientation of the bias diode and bias filter capacitor.

    Then I crank up with rectifier only, check voltage on bias, B+ and filaments.

    Then output tubes, with speaker now connected too. Check again.

    Then preamp tubes, check again.

    Then crank it up, and see if it squeals like a rabid Jubjub Bird getting laid. If not, all's well. If so, reverse speaker ground with speaker hot.

    Done.

    There are probably other things that I can't seriously remember until I actual do 'em, I'm sure.


    *Yosemite Sam on TV as we speak
     
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  14. Cjsinla

    Cjsinla Premium Member

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    You called it. My 5e3 sounded like crap yesterday. I checked it out and it was the jacks. Good idea about the construction paper. I was thinking about polishing sandpaper, 1200 grit. I was gonna try contact cleaner first but I can’t find my trusty can of Radio Shack contact cleaner.
     
  15. Leña_Costoso

    Leña_Costoso Senior Member

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    Nix the sandpaper. Those contacts just have a little left over crud from manufacturing on them. Make sure the spring tension is good. Run some coarse paper through. That will pretty much do it.
    Even with very fine sandpaper you're going to remove some of the plating. It will probably be better for a while but with no plating it's liable to get cruddy again faster
     
    Last edited: Dec 3, 2017
  16. D'tar

    D'tar Senior Member

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    On this analog meter do you adjust it before using. Put meter on ohms, short leads together and adjust needle to zero?
     
  17. Leña_Costoso

    Leña_Costoso Senior Member

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    The adjustment you describe for analog meters only affects the ohms reading not the voltage readings.
     
  18. Cjsinla

    Cjsinla Premium Member

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    The DC scale only reads to 250v but you can set the selector to 500v. I assume that means that you double what the needle reads, which was about 205v for the B+ voltage. That would translate to 410v.
     
  19. Leña_Costoso

    Leña_Costoso Senior Member

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    That's one way to look at it. Another is to take the 50vDC scale and put a zero on the end of it.

    I've owned, I think, four Simpson 260's, one was an old 260-6, the rest 260-8's. The new ones are still "ok", but they changed to plastic "glass" on the front. Reasonable care will keep it scratch free, but.... the plastic picks up static that throws their highly sensitive movement out for a walk in the woods.

    Analog meters come in three flavors: galvanometer, FET, and VTVM.

    Of those the simple galvanometer type will measure voltage directly, even with no battery in the meter. The battery(s) are for ohms only, and provide a reference voltage for the meter to read against, and thus know what the ohms are. The voltage scales are taken care of directly with resistors, and some diodes for AC. The reason for "ohms adjust" is to take into account the aging and lowering of the battery reference voltage.

    Analog meters using galvanometers have sensitive movements, because they have to provide a very low load to the circuit being tested. They're rated in "ohms per volt". The Simpson 260 has 20,000 ohms per volt. Ohms per volt is the amount of ohms the meter itself presents as a load to the circuit, based on the max scale of the meter. So, for the 260's 1000vAC/DC scale, the 20,000 ohms per volt would be a 2,000,000 ohm resistive load, not much. Most cheap meters of this type are in the 5,000 or 10,000 ohms per volt, which is still fairly good for our use.

    The problem with galvanometers is they're fiddly. To get around the fiddly nature and sensitive structure, some smart SOB came up with the idea of using a tube to amplify the voltage that would have been normally given to the small, sensitive, fiddly galvanometer, and send it to a more robust galvanometer. Those meters are called VTVM, or Vacuum Tube Volt Meter. They're more sensitive, and present a very very small load, in the order of 1meg to probably over 20megohms per volt, as that's the nature of tubes. But, they require complex calibration, a way to regulate or adjust the power supply, and continued calibration as the tube ages and goes soft. Ugh.

    Next up.... the FET Voltmeter. Same as a VTVM, but less subject to continual adjustment, but more subject to "zzzaaaaap" of the FET front end. No free lunch. Still uses an amplified voltage, fed by a battery or transformer, to feed a more robust meter movement.

    Finally we got "digital" meters, which have continually improved, have all sorts of zzzaaapp protection these days, and are as low load, and better, than the best VTVMs were, back in the day. Naturally, they need batteries to run.

    Someplace, I have an old Radio Shack "Micronta" digital volt meter that I bought back in about 1978 or so. What a joy to use back then compared to the Mura or Simpson meters. Fluke had not yet presented itself to the masses with meters. I think they got started in digital about 1975ish, give or take a year or two. The mainstay was the Simpson 260, it was king of the hill, top dog.

    Gone thru a lot of meters over the last 50 years of screwin' around with electronical apparatus. I'm sure the best is yet to come.....
     
  20. Cjsinla

    Cjsinla Premium Member

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    That idea you had about using paper to clean the input jacks worked great on my 5e3. I’ll go back through the Super next.
    @Leña_Costoso
     
    Last edited: Dec 5, 2017

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