The Right Filter Choke Question?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by jh45gun, Mar 21, 2008.

  1. jh45gun

    jh45gun Member

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    OK I am building a Tweed Super 5f4 and about the only thing I need left to order is the Filter choke. Is this the proper one?

    CHOKE, HAMMOND, REPLACEMENT FOR FENDER

    Equivalent to 022699, 125C1A, 90ma/1500 ohms, 4 Henrie inductance. For Bandmaster, Bassman, Concert, Dual Showman, Pro Reverb, Super Reverb, Twin Reverb.
     
  2. phsyconoodler

    phsyconoodler Member

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    Yes,it is the right one.
     
  3. Trout

    Trout Member

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    Your going to be pulling as much as 200ma or more through that choke!!

    The one you listed will most likely live a very short life. That would be ok in some of the blackface and later amps, but not in the earlier tweeds.

    You need something in this in this range. Triad Choke

    In those amps the choke is only handling the Pre-Amp a Screen curent, In the 5F4 you are filtering ALL the output current.
     
  4. jh45gun

    jh45gun Member

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    Thanks Trout I appreciate the advice and the link! That is what I will order. Jim
     
  5. phsyconoodler

    phsyconoodler Member

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    If you look at the scheamtics the AB763 and the 5F4 super,the only difference is the choke on the 5F4 is after the first filter cap and the AB763 is before the first filter cap.The current draw looks to be the same.
    Correct me if I'm wrong,but both are filtering DC and both go to power tube screens and OT centre tap.Both chokes are before everything in the whole amp.

    And furthermore,the 5F4 super schematic lists the choke number as 125C1A,which incidentally is the same as the Hammond 194B. Both amps use the same choke and there is no output filtered by the choke.
     
  6. Trout

    Trout Member

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    In the AB763 the OT/ CT is ahead of the choke and not being filtered by the choke. IE Only the screen,and pre-stages are filtered by the choke.


    In Models 5F4, 5E7, 5E6A, 5E5, 5E8A The entire amp is supplied through the choke, OT/CT as well as the screens and pre-stages. The choke in these models is subjected to up to 200ma.

    5E4-A Is a 6V6 PP amp, a 90ma choke part number Hammond 194B is acceptable.
    5F4 is a 6L6 PP amp and will require a choke that can handle 200MA.
     
  7. phsyconoodler

    phsyconoodler Member

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    However,the 5F4 has the part number listed on the schematic as 125C1A which is a 90ma choke.
     
  8. EarlTX

    EarlTX Member

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    Weber sells a 200mA choke for tweeds for $25.

    Choke for Tweed Fenders. 5-8H @ 200ma, 125 ohms, 3-9/16" mounting.

    W014684
     
  9. Trout

    Trout Member

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    Yep, 200ma, or the Triad I listed above which is $16.00 ( Data Sheet ) also 3 9/16ths mounting centers.

    5F4 Link
    Choke=14684 For (6L6 Amps)

    5E4-A
    Choke = 125C1A
     
  10. jh45gun

    jh45gun Member

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    Again thanks guys I am going to go with the Weber Choke just for the simple reason I need Pots too and his pots are reasonable and if I found a place that had reasonable Pots they did not have the choke. If I found a place that had the choke like Allied their pots were expensive. While Weber's Choke is a bit more in price for what I save in pots and shipping should equal out or be a bit cheaper than ordering from two places for the choke from one and the pots from another. Again thanks for the help.
     
  11. phsyconoodler

    phsyconoodler Member

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    Thanks Trout for not letting my late-nite tunnel vision to cloud the issue!
    I don't quite uderstand why a 5F4 choke needs to be higher current than the AB763 though.By moving the plate supply line to one side of the filter cap or the other?Would the current draw not be the same as they are all in line after the first filter cap?
     
  12. Trout

    Trout Member

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    No Biggie,, I went back and looked it up again and then compared my service sheets to several of the tweeds Vs the AB763.

    In summary, this is why. The bulk of current is required at the OT center tap. In a lot of the old tweed circuits the CT is actually attached after the choke rather than before. as follows
    5F4 Cap,--> Choke -->Cap & CT,-->
    AB763 Cap & CT -->choke-->Cap-->

    That is one of the reasons that the old tweeds have such charm, There is a long reaction time in a choke fed supply.

    :BEER
     
  13. jh45gun

    jh45gun Member

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    Well technical stuff aside I am just glad you pointed me in the right direction. I would have been disapointed buying the wrong part then have it fail and wonder why it did. Jim
     
  14. VikingAmps

    VikingAmps Member

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    Actually its still a cap input supply. It's just that the choke has the power tubes plate current flowing thru it as well with this arrangement. Cap input supplys have a slower reaction time and are more saggy than a choke input supply.
     
  15. Trout

    Trout Member

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    Yes,
    that is correct, As I am certain you already know, In many amps the use of a resistor in place of the choke is very common practice, this improves response times.
    The reaction swing on the choke is very slow comparatively, this compounds the sag in either choke input or cap input when the power tubes receive their current thru the choke.
    Point being that this is part of what made that particular era/series of tweed amps unique.
     
  16. VikingAmps

    VikingAmps Member

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    That's funny I always thought you got more sag/slower reaction with a resistor than a choke since there is a greater DC drop across it.
     
  17. tommytomcat

    tommytomcat Member

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    Would it hurt anything? drastically alter the tone? damage anything?if the 5f4 was wired with the first filter cap(s) feeding the OT was placed before the choke?
     

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