5f4 / 5e7 build

Discussion in 'Shock Brother's DIY Amps' started by theprofessor, Feb 2, 2019.

  1. D'tar

    D'tar Friend of Leo's

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    And 200+vdc

    Yes. We're all still watching Professor:)
     
  2. theprofessor

    theprofessor Friend of Leo's

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    Hey D'tar! Anything you'd change about it? I don't know if I can get it out easily at this point, but perhaps I could put some fiberboard on the back of that pot or something. Thoughts?
     
  3. theprofessor

    theprofessor Friend of Leo's

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    This gives a sense of the spacing from a better angle. It's about as narrow/thick as a piece of fiberboard.

    IMG_1037.JPG
     
  4. D'tar

    D'tar Friend of Leo's

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    That angle looks better Professor. It's still close but not as bad as it looked in the other photo. If theres a washer on the pot inside the chassis maybe remove it to increase the clearance.
     
  5. theprofessor

    theprofessor Friend of Leo's

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    Thanks! Yes, there's a lock-washer. I'm going to see if I can get it out and give it some more space. We'll see...
     
  6. D'tar

    D'tar Friend of Leo's

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    Sweet. Can't wait for the Vintage Tone Report!
     
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  7. theprofessor

    theprofessor Friend of Leo's

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    OK, that wasn't so bad. I got it out without much hassle, took the internal-toothed lock washer off, and I gained some more clearance. It looks a "lot" better to me.

    IMG_1038.JPG
     
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  8. theprofessor

    theprofessor Friend of Leo's

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    I got the heater wiring finished last night. Today I'll go through the startup procedure, and I'll report back here.

    IMG_1046.JPG
     
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  9. FenderLover

    FenderLover Friend of Leo's

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    You've been busy building lately, Prof. Can we also get a family pic when you're done?
     
  10. theprofessor

    theprofessor Friend of Leo's

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    Will do!
     
  11. theprofessor

    theprofessor Friend of Leo's

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    I just went through the startup procedure. Here are the voltages and such. The only thing that seems odd is the ca. 206 volts on the V2 grid (pin 7) and on the V2 cathode (pin 8), but I'm supposing this has to do with the fact that pin 7 is tied to pin 1 (plate) in this design.

    loaded voltages (exactly what I was shooting for!)
    B+1 407 DCV
    B+2 401 DCV
    B+3 325 DCV

    heaters at 6.64 ACV

    Currently, my bias range is from -37.3 to -25.6. Now I've got to work on biasing for these 5881s.

    5F4 startup voltage chart

    Before starting, do a continuity check from the sleeve of an instrument cable that is plugged into each input to the ground of the power cord. In addition, do a continuity check between the sleeve of an instrument cable that is plugged in to the speaker output jack and the ground of the power cord.

    Done.


    1. Plug in the amp

    2.-3. Turn the amp on

    Measured in AC volts

    AC wall voltage: 121.5 ACV

    Fuse -- ACV

    Power switch -- ACV

    6.3V pilot light works

    Power transformer output (AC)

    Heater voltage (AC) [goal: ca. 5.7 – 6.9 ACV] 3.44 ACV = 6.88 ACV

    Rectifier heater voltage (AC) [goal: ca. 4.5 – 5.5 ACV] 5.41 ACV



    5U4

    Pin 2 (heater) to Pin 8 (heater) = 5.41 ACV

    Pin to ground measured at pins 3 and 4, because I have SS diodes between 3->4 and 5->6

    3->diode->4: 344 ACV

    4->diode->5: 344 ACV


    Heater pin voltages (AC) on power and preamp tubes (goal: ca. 6.3V):

    5881 (V4 and V5)

    Pin 2 (heater filament) to Pin 7 (heater filament) = 6.9 ACV

    Pin 2 (heater filament) to Pin 7 (heater filament) = 6.9 ACV

    12AY7 (V1)

    Pin 4 heater to Pin 9 heater center tap = 6.9 ACV

    Pin 5 heater to Pin 9 heater center tap = 6.9 ACV

    12AX7 (V2)

    Pin 4 heater to Pin 9 heater center tap = 6.9 ACV

    Pin 5 heater to Pin 9 heater center tap = 6.9 ACV

    12AX7 (V3)

    Pin 4 heater to Pin 9 heater center tap = 6.9 ACV

    Pin 5 heater to Pin 9 heater center tap = 6.9 ACV


    4.-5. Install Rectifier tube and power on, using lightbulb limiter

    Measured in DC volts

    Rectifier output (pin 8): 483 DCV

    B+1 measured at first filter cap: 483 DCV

    B+2 measured at second filter cap: 483 DCV

    B+3 measured at third filter cap: 483 DCV

    Preamp tube plates (pins 1&6): V1, pin 1: 474 DCV

    V1, pin 6: 474 DCV

    V2, pin 1: 475 DCV

    V2, pin 6: 482 DCV

    V3, pin 1: 476 DCV

    V3, pin 6: 480 DCV

    OT connection to power tube (5881, pin 3): V4, pin 3: 485 DCV

    V5, pin 3: 485 DCV

    All tube pin voltages (heaters are AC)


    6. Install all the Preamp tubes and power on, using light bulb limiter

    Measured in DC volts

    12AY7/12AX7 cathodes (goal: 1-2 DCV):

    Pin 3: V1: 2.7 DCV

    V2: 1.62 DCV

    V3: 1.74 DCV (phase inverter)

    Pin 8: V1: 2.7 DCV

    V2: 206 DCV

    V3: 70 DCV (phase inverter)

    12AX7 grids (goal: 0 DCV):

    Pin 2: V1: .1 DCV;

    V2: .2 DCV

    V3: .7 DCV (phase inverter)

    Pin 7: V1: .1 DCV

    V2: 204 DCV

    V3: 11.76 DCV (phase inverter)

    5881 V4, pin 5 (grid)

    -25.6, then adjusted the pot all the way to the right to get -37.3 DCV (the most negative voltage)

    5881 V5, pin 5 (grid)

    -25.6, then adjusted pot all the way to the right to get -37.3 DCV (the most negative voltage)

    [Adjust bias pot for largest negative DC voltage possible.]

    Note: with a 22k resistor + 10kl bias pot, my bias range is from -37.3 DCV to -25.6 DCV


    7. Install 5881s, hook up to speaker, and take measurements

    Measured in DC volts

    The power tubes did not redplate

    V4: 5881

    Plate, Pin 3: 400 DCV

    Screen grid, pin 4: 404 DCV



    V5: 5881

    Plate, Pin 3: 400 DCV

    Screen grid, pin 4: 404 DCV


    V1: 12AY7

    Plates, pins 1 and 6

    Pin 1: 145 DCV;

    Pin 6: 144 DCV


    V2: 12AX7

    Plates, pins 1 and 6

    Pin 1: 177 DCV

    Pin 6: 271 DCV


    V3: 12AX7

    Plates, pins 1 and 6

    Pin 1: 222 DCV

    Pin 6: 265 DCV


    B+1: 407

    B+2: 401

    B+3: 325


    I re-measured the heaters (ACV), and they’re at 3.32V each, thus 6.64 ACV
     
    Last edited: Feb 9, 2019
  12. theprofessor

    theprofessor Friend of Leo's

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    I got it fired up, and this is a really great-sounding amp! I had to reverse the OT leads, though I was surprised that the very high-pitched squeal artifact wasn't as obvious as it has been in the past.

    I'm still having one issue: At high volumes and especially when the bass is turned up above about 2 and when I dig into the bass strings on the guitar, I get a sort of fizzing/crackling sound (it's not my guitar fretting out or nut rattle). It sounds like a loose connection somewhere or something. I checked the OT wiring to the speaker jack and the speaker connections (which I might now solder), but I haven't found anything so far. I can play the amp on the normal channel at 9 with it sounding great, but occasionally, I get this crackle on the bass notes. Thoughts?
     
  13. King Fan

    King Fan Friend of Leo's

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    Electrical crackle or mechanical vibration do you think? Both have dozens of possible suspects. It took me days to decide which I had, and more to track down the cause.
     
  14. theprofessor

    theprofessor Friend of Leo's

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    Yes, I was worried about that. It seemed like it could be just about anything! I soldered the speaker leads. Not that. I changed preamp tubes. Not that. Then I pulled out the trusty wooden chop-stick. The lead to the right lug of the treble pot wasn't fastened securely enough, and it just fell out. I re-soldered it, and all is well. This amps sounds absolutely fantastic. And I'm leaving the 10M local NFB resistor. I wouldn't want it spec, I think, at 4.7M for the 5f4.

    These vintage Tung-Sol 5881s sound great!
     
    Last edited: Feb 9, 2019
  15. theprofessor

    theprofessor Friend of Leo's

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    Tubes:

    V1: 1953 GE (= Ken-Rad) 12AY7 gray box plates, labeled "Tung-Sol"
    V2: 1950's RCA 12AX7 long black plates
    V3: Groove Tubes ECC83 [I need to understand the nature of phase inverter distortion better before I know what to put here; I chose the Groove Tubes because I thought it had the best chance of matched triodes, but not on the basis of distortion/harmonics characteristics]
    V4: vintage (didn't look at the date) Tung-Sol 5881 brown base, labeled "RCA"
    V5: vintage (didn't look at the date) Tung-Sol 5881 brown base
    V6: JAN Phillips 5U4GB

    IMG_1047.JPG IMG_1048.JPG
     
  16. theprofessor

    theprofessor Friend of Leo's

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    And now, because @FenderLover requested it, some "family" photos of my amps. I had to sell my 5f2a to raise money for this one (boo), and the BF Princeton Reverb I built was for someone else. But I've got plenty left!

    Over on the left on the stand is my Surfy Bear reverb build. My 5f2a used to tuck right under it. In back is my 5e3 "Honey Deluxe" head and my Fender tweed extension cab, loaded with an Eminence Red Fang alnico 12". In front of that is my '76 Deluxe Reverb with an Eminence Josh Smith 1250. And in front of that is my "Lenox-Amp" 6G2 clone, with an Eminence GB128.

    IMG_1049.JPG


    Now the 5f4 tweed Super (my name is TBD) has joined the gang. You can see the size relative to the 6G2 and the DR.

    IMG_1050.JPG

    And here's a side shot to show the size difference between the 5f4 and a vintage Deluxe Reverb. The 5f4 cabinet is slightly narrower and an inch or two taller. My 5f4 is lighter than my Deluxe Reverb, because the DR has that dang MDF baffle!

    IMG_1051.JPG
     
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  17. theprofessor

    theprofessor Friend of Leo's

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    This thing is just magnificent! It's a tweed, but it's like the anti-5e3. Where the 5e3 wants to growl and give you thick mids right off the bat, this one wants to stay clean longer, is very articulate, and is not at all too bassy (this lack of bass also has to do with the speakers; I prefer it). If I use my LP with P-90s with a 5e3, I pretty much need to use the neck pickup to have any good articulation. If I play through the 5f4, I can use the neck pickup on all my guitars (including the LP) with no problem. It still sounds great. I haven't even switched to the bridge pickup on either my Tele or my LP with this 5f4, because, well, I don't think that would work out so well for my ears. That said, the bridge pickup through a 5e3 and the neck pickup through a 5f4 are not at all the same.
     
  18. theprofessor

    theprofessor Friend of Leo's

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    Does anyone know where I can find the dimensions of the metal badge that went on the front of the "Fender Super-Amp"? I'd like to have a custom one made, but I'd like the dimensions to be the same as the originals, provided there was a standard.
     
  19. theprofessor

    theprofessor Friend of Leo's

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    I continued to have some crackles and the like from time to time. I thought for sure it must be microphonic tubes, but after lots of tube swapping, nothing really changed. So I got out the chop stick again.

    It turns out that while I had wrapped the h#ll out of two 100k resistors that lead to V1, pins 1 and 6 (plates of each triode) and then on to various other components, including the last filter cap, I hadn't soldered them around the top-most lug.

    I thought I had done so well by doing continuity tests on every component, but I needed to do more tug-tests!

    Before
    IMG_1053.JPG

    After
    IMG_1054.JPG
     
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  20. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

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    Looks good my man. Now, can we get a little sound sample?

    (I'm really jonesing to get another build going... Need to get my shop set up again after my move!)
     
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