Tweed 6v6 dropping resistor values

Discussion in 'Shock Brother's DIY Amps' started by jsnwhite619, Jan 10, 2020.

  1. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I've been looking through schematics & layouts and noticed something on there. I did a little searching about it and didn't really come up with much, so I'll try it here. Is it a common mod to reduce the 4.7k dropping resistor in a 5e3 for any added benefit?

    Comparing a 5f10, 5f11, and 5g9 with it, you get

    5f10:
    305v > 470R > 302v >22k > 250v

    5f11:
    340v > 470R > 330v > 22k > 260v

    5g9:
    370v > choke > 368v > 10k > 247v

    Then, using Rob's site's voltage chart, the 5e3 has
    370v > 4700R > 318v > 22k > 247v

    Why the 10x sized dropping resistor in the 5e3? The others drop 1-2% after that first resistor, but the 5e3 drops down 15-16% in the same place. Like I said, I didn't exhaust the internet looking for answers yet - they are usually all here anyway ;) - but I was just curious if anyone here was tried knocking that back 80-90% and what was the end result?
     
  2. Phrygian77

    Phrygian77 Tele-Afflicted

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    Your talking about the screen grid node resistor, right? Lowering it is going to rotate the load line counter-clockwise. I think part of what makes the 5E3 output sound like a 5E3 is the low plate to cathode voltage, the lowered screen voltage, no screen grid resistors, and the 8k primary. And, obviously, no NFB. Changes will affect the harmonic distortion character.

    Just chiming in. I'm no expert on tweed amps at all.
     
  3. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Yeah, I'm not getting into the "it's not a 5e3 anymore" aspect. Just, with the grocery list of mods people do to them to wring something else out of them, it's not something I found info on easily.

    Comparing the 5f11 & 5e3, Deluxe voltage B+ starts 30v higher and ends 13v lower in the preamp node. 5g9 starts the same 370v, uses a choke, and the Tremolux ends up 63v higher in the preamp node. Basically, again, I wonder why Fender went with such a large value dropping resistor there when other similar amps were using much smaller values or a choke. Either way, voltage dropped a lot more on the 5e3 than other similar amps.
     
  4. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    The Deluxe is the only cathode biased of the amps you list, therefor the only one to have Ca. 20 volts on the 6V6 cathodes. The other three all have fixed bias, and the cathodes at 0V.
     
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  5. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Well, there you go. I figured it was a simple explanation!
     
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