Guyatone GA-430 volume pot Question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by PawleeP, Dec 26, 2017.


  1. PawleeP

    PawleeP Member

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    Guyatone GA-430 Question
    This may be off topic.. but, i figured someone have an answer.
    have a guyatone combo w/2 EL84's in pwoer section ( GA-430 i think) and the mstr (only volume) pot is a A500K (reads 625k) with an on/off switch piggybacked and intermittent. All i can find with a switch is a 1meg 1000k ohms. Will this make the amp brighter. Because all it has is a tone for EQ and i may not want it brighter..
    Also will this overload anything in the pre-amp or power section? thanx, p. surrounded by death

    What wattage and value do i need for volume on this?
    The rest of the pots (originals) are mostly VIOLET N - 24 's and read about 580k


    P
     
  2. pdf64

    pdf64 Member

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    Last edited: Dec 27, 2017
  3. PawleeP

    PawleeP Member

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    I did find a full sized bournes A500K that i may be able to make work! But, it reads 435K on meter. Not sure which way to go? 970K or 435K? I imagine wall power is around 117 around here!
    thanx, p
    Having a hard time figuring out where the Volume Pot is in that diagram.. shux!
     
  4. pdf64

    pdf64 Member

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    What do you think is the problem with it measuring 435k?
    VR2, connects to board terminals #4 and #5
     
  5. PawleeP

    PawleeP Member

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    Thanx pdf64!
    I guess the main question I have is: What effect on tone will the volume pot have on tone? if any! Is it similar to the affects on brightness/timbre as changing the pots on a guitar?

    I now have a choice between the A435k , original A625K (i repaired the pot, but piggybacked switch is trashed) and a A975K.. I also temporarily added a dedicated on/off switch, until i know what is best!
    Thanx, p
    Any suggestions on what would be best, very much appreciated!

    <a little off topic, BUT>
    (new thread started) "Washburn MG-70 i am restoring and need advice"
    Also have a washburn mg-70 i am restoring and need advice on this too.
    Trying to keep it as close to original as possible.
    But; am interested in the best pots even if they are the bournes ones that cost almost 10 bux a piece, this guit-fiddle has a high level of sentimental value. is an early nineties and is green. May look for other threads for help, or start a new one.
    the tone is a push pull (for tapping the br. pup, i suppose)
    Have no idea what value(s) are best for original pups.
     
    Last edited: Dec 28, 2017
  6. PawleeP

    PawleeP Member

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    Am kinda hesitant about ever turning this thing on until i know for sure what value volume pots(s) would be best ?
    And is there any chance of hurting the Amp with the A975K?
     
  7. HotBluePlates

    HotBluePlates Member

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    No.

    500k. 1M. Just replace the pot, it will be fine.
     
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  8. Dan40

    Dan40 Supporting Member

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    I left you some possible solutions on your thread at the Tele Forum.
     
  9. PawleeP

    PawleeP Member

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    Most pots are 10% tolerance so it is very rare to find one that measures dead on it's specs. Older pots may be off as much as 20% or more. If you are dead set on keeping the switched volume pot but cannot find a 500k, you could parallel a 1 meg resistor over the 1 meg pot to make a 500k. Another option is to just use a standard 500k pot and add a small switch on the back panel to power the amp up and down, or...if the tone pot is 1 meg, simply purchase the 1 meg switched pot and use it for the tone control and replace the volume with a standard 500k audio. Those are a couple of options for you to think about.
    I added a separate switch already (maybe temporary), so i just want to know if there are any possible adverse affects (such as too much timbre or brittleness like when you increase aguitar vol pot) if i go with the 975k i have already installed or go with a lower values 625K or 435K.. appreciate the help! p
     
  10. pdf64

    pdf64 Member

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    Tolerance is a key part of any engineering specification. No real world item can be 'dead on', exactly its nominal value, hence an acceptable tolerance must be provided.

    My perception is that most commonly available commercial grade pot types intended for guitars and amps have a 20% tolerance spec; if it's not noted then that is the safe assumption. A 10% tolerance on a pot is usually noted, as it's an exception to the norm.

    A volume control in a guitar is usually a key part of the pick up's resonant circuit, and the resonance characteristics will alter as the pot value is changed, see http://www.buildyourguitar.com/resources/lemme/
    The tone/vol circuit in your amp is not resonant (at least within the audio range), but its frequency characteristics will alter somewhat with the vol pot value.
    You are in the best position to try them all and assess which one you like the best.
    If in doubt then perhaps use the one closest in value to the schematic.
     
    Last edited: Dec 30, 2017
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  11. PawleeP

    PawleeP Member

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    nice recordings.. did you guys have 2 different bassists?
    some of the other songs must be from earlier years or something?
    Is that natural bass a P? kinda sonds like one, but is hard to tell from pics!
    thanx for all the help, p
     

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