New 5F2A build!

Discussion in 'Shock Brother's DIY Amps' started by SebC, Dec 12, 2019.

  1. King Fan

    King Fan Friend of Leo's

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    Heh, I wondered if you were doing it on purpose. Never thought about the shorter leads; I just do what Leo did. As long as you don't get confused about which lug is which, and as long as those lugs and leads don't get in the way down there, you have my permission to do whatever you want. Well, in this regard anyway... :)
     
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  2. SebC

    SebC Tele-Meister

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    I am indeed using JJ 6V6S. But would it still be a good idea to increase the cathode resistor? To what value?
     
  3. SebC

    SebC Tele-Meister

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    Too late! Jaja
    22B32FC2-00B4-4CC5-B50E-8409D01939B3.jpeg
     
  4. jimgchord

    jimgchord Tele-Afflicted

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    You wont really know until you build it and take measurements. Something in the 560 ohm area. again, you may not need it but im guessing once you measure you will be just over max diss.
     
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  5. SebC

    SebC Tele-Meister

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    I'm back and finally getting started. I have encountered a little stumbling block straight away:
    I decided to start by assembling the ground buses first
    45B34ED0-D726-42CD-902D-CF43A4D58E11.jpeg
    Since I'm grounding the V2 power tube grid leak, and the power tube cathode resistor and bypass cap to the first filter capacitor's ground instead than to the signal ground bus, I have an eyelet deficit because I'm moving the 22k and 1.5k resistors (that go to pin 4) away:
    516016C9-898B-4B6A-8A29-ECA880EA74CF.jpeg
    Would it be OK to solder the lead of the 1.5k resistor directly on the ground bus?
    Something like this:
    D9CF73F3-958B-4742-96CE-820F2B13C321.jpeg

    Or is it not worth the trouble and I just keep it as in the weber layout: the 1.5k resistor, the 25uf, the 470 and the 220k all into the same eyelet and to the signal ground bus?
     
  6. King Fan

    King Fan Friend of Leo's

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    Sorry, why are you using the Weber layout here instead of, say, Rob's?

    upload_2020-1-10_9-40-40.jpeg

    And remind us why you want to ground the 220Ks to the power amp ground. Not that it'd be hard, on this layout, to move their ground wire to the power amp bus.
     
  7. SebC

    SebC Tele-Meister

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    @King Fan, I'm not really using weber's layout, it just serves here to show the eyelets available on my eyelet board. I am in fact using my own layout (bottom right in pic) which combines what I've considered to be best practices from robs layouts and suggestions on this thread.
    2AEC6386-863D-4401-98A9-6B9637E84BD8.jpeg
    And I'm referring to a few others back and forth including rob's 5f1 layout -not in pic but on my phone :) -
    I want to ground the 220K, 25uf and 470 to the power amp ground based on Rob's 5f1 layout and this statement on his website:
    "Grounding the V2 power tube grid leak (R9) and the power tube cathode resistor (R8) and bypass cap (C6) to the first filter capacitor's ground (C3) is best practice and should result in a quieter amp"
     
  8. King Fan

    King Fan Friend of Leo's

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    Oh, right, this was a 5F2a. Duh, sorry. Ignore my comments...
     
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  9. SebC

    SebC Tele-Meister

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    No worries!
    I just want to know if it's OK to solder the lead of that 1.5k resistor right on the preamp ground bus wire
     
  10. SebC

    SebC Tele-Meister

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    In the mojotone small parts kit, what should be the 220K resistor gives me this reading.
    7E4B681D-4113-420A-9146-88F7481EBC45.jpeg Is that a weird way to display 218K? Why would it read in megaohms as .218 M Ohms?
    I guess it's OK to use?
     
  11. Paul-T

    Paul-T Tele-Meister

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    Kilo = 1,000, Meg = 1,000,000 so 218k = 0.218M
     
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  12. SebC

    SebC Tele-Meister

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    Great!
    I was puzzled that the meter wouldn't just show 218K

    Good to confirm I can use it
     
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  13. mabinogeon

    mabinogeon TDPRI Member Silver Supporter

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    I think I'm confused by your grounding scheme. Here's a very solid 5F2A layout (from Mojotone). But I don't like how they wire the mains - I use Weber's layout for that (minus the wire nut. Heat shrink that connection).

    I'm in the middle of making my own 5F2A, and this is what my board looks like:
     
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  14. SebC

    SebC Tele-Meister

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    Thanks @mabinogeon for sharing that layout! I hadn't seen that one.
    And wow, that's a great looking board!!

    Yes, I'm deviating just a little from most grounding schemes I've seen for this amp based on @robrob's 5f1 layout. He explains that grounding the V2 power tube grid leak (220K resitor) and the power tube cathode resistor (470 ohm) and bypass cap (25uf) to the first filter capacitor's ground (C3) is best practice and should result in a quieter amp.
    26EDC6A9-8DE3-4D52-A0F9-7B7CD0AE52FE.jpeg
    I also added most suggestions I've received on this thread like all your great suggestions on post #17 plus the elevated heaters thing. This is my resulting hand drawn layout:
    65521C2D-2119-4CF1-8B8A-BA9407BAF66A.jpeg
     
  15. King Fan

    King Fan Friend of Leo's

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    Your work on those drawings is impressive. I'm not sure tho: Do you still have an eyelet problem?

    I think Rob shows the grid leak ground you mention on his 5F1 layout below. Note he just runs a black wire (which could go under the board) to the reservoir cap negative. BTW the "power amp ground bus" could be another black wire (often also run on the back) between the first two filter caps, or a bus wire between them as drawn. Heck, the wires could be purple or white or green (if they're behind the board). In any case, no need for a big explicit bus to extend over to the cathode bias sector.

    One thing Rob hasn't revised on that 5F1 layout is his more recent idea to run the HT center tap straight to the reservoir negative pole. See his current 5e3 (which I mistakenly posted in #46 above) for an example -- he mentions the rationale on his 5e3 mods page...

    5F1_Layout.png
     
    Last edited: Jan 11, 2020
  16. SebC

    SebC Tele-Meister

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    I realized that if I solder the lead of that 1.5k resistor directly to the preamp ground bus wire (as in rob's 5f1 layout) then I have enough eyelets!

    Cool! @Mongo Park suggested to run that center tap to pin 8 of V2 for the same reason.

    Can't wait to keep smelling more of those solder fumes...hope to have pics of the populated board this Wednesday
     
  17. King Fan

    King Fan Friend of Leo's

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    Whoa. Which CT? Which same reason? :)

    The heater CT (grn/yel) would go to the power tube cathode to elevate the heaters, which fights heater hum. The HT CT (red/yel) would go (per Rob) to the reservoir cap negative, which fights ripple hum.
     
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  18. Paul-T

    Paul-T Tele-Meister

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    Don't understand that one.. is Pin 8 really at earth potential????
     
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  19. King Fan

    King Fan Friend of Leo's

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    I think, Paul, we had some wires crossed (literally). See if my guess makes sense.

    Oh, but on the first question Seb, you're exactly right -- a resistor or capacitor lead can go to a ground bus, if the bus is rigid/stout enough to support it.

    upload_2020-1-11_12-43-40.png
     
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  20. SebC

    SebC Tele-Meister

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    Sorry! I see I am confused. So yes, the heater CT grn/yel is what I'm sending to pin 8 of V2.

    Now, is this what you mean about the HT CT? 6032F990-4572-42B7-AECF-799E2097AC9F.jpeg
     
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