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Substituting transistors in a simple boost (Germanium for silicon)

Discussion in 'The Stomp Box' started by closedmri, Mar 14, 2021.

  1. closedmri

    closedmri TDPRI Member

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    Hey all,

    I’m thinking of making a simple boost circuit like the LPB-1 with a germanium transistor instead of silicon. I’m curious if this will require different capacitor & resistor values or any other finagling of the circuit to compensate for the different transistor? Or more simply put, can a germanium transistor act as a drop-in replacement for a silicon one and vice versa?
     
  2. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Have a look at
    Germanium Giant Tagboardeffects
     
  3. DADGAD

    DADGAD Friend of Leo's

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    A Germanium transistor will require different bias resistors. It is not a drop in replacement for a silicon device. You might be better off building a Rangemaster with selectable input capacitors. I made one and it sounds very nice.

    By selectable I mean a potentiometer with a series capacitor in parallel with the .005uf input capacitor.
     
    Last edited: Mar 15, 2021
  4. closedmri

    closedmri TDPRI Member

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    [Message deleted]
     
    Last edited: Mar 15, 2021
  5. closedmri

    closedmri TDPRI Member

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    Funny, that was one of the last sites I was on before coming here with my question. He added a trim pot which is something I was interested in trying as well. But I wasn’t entirely sure his circuit was what I was looking for (I’m schematic illiterate and working on it). Nevertheless I will take a closer look. Thanks!
     
  6. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    The germanium are more finicky so trim pots can be helpful to get them dialed in. You can replace the trim pot with a resistor once you like how it responds.
     
  7. closedmri

    closedmri TDPRI Member

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    Makes sense. I have a rangemaster-style treble booster with a toggle switch that can make it a full range or mid range boost. Maybe I should focus on that circuit for achieving my goal.
     
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  8. DADGAD

    DADGAD Friend of Leo's

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    Good idea. Just remember to heatsink the leads on germanium devices when soldering because they are easily damaged by heat.
     
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  9. closedmri

    closedmri TDPRI Member

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    I have not yet grappled with the reality of my idea, but it is essentially to replace the output pot with a trim/gain pot like you said and add a bass cut pot somewhere in the circuit as well.
     
  10. closedmri

    closedmri TDPRI Member

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    Thanks for the heads up. I have a little clip for that but it doesn’t function as well as I’d like. Is it important to have the transistor connected to a heat sink after soldering to transfer electrical heat from a power supply?
     
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  11. Oldsmobum

    Oldsmobum Tele-Holic

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    When I was building a range master with a silicon transistor, almost all of the schematics were for germanium and thus had those bias values. I soon found out that calculus was required to calculate the values to bias my silicon transistor... I never took calculus. So I copied the bias circuit from a Naga viper. Thankfully it worked, because I’ll quit guitar before I take calculus.
     
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  12. DADGAD

    DADGAD Friend of Leo's

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    I use a small aligator clip on the germanium device, only on the lead I am soldering. When done, move to the next lead and repeat the process. Solder quickly and remove the iron ASAP. A germanium transistor in a Rangemaster type treble booster does not need a heatsink. Use the same technique when soldering germanium diodes. Silicon devices are less likely to be damaged by heat from solding. However soldering silicon devices should be completed in 5 seconds or less.

    Feel free to ask questions. There are many good people on TDPRI willing to assist you.

    Good luck!
     
  13. DADGAD

    DADGAD Friend of Leo's

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    If you want to build a Rangemaster type pedal using a silicon device, you could copy an MXR LPT1 booster and play with the input capacitor value to get the tone you like. Of course, you won't get the same mojo toanz that germanium offers.

    But most electronics calculations needed for hobbyist guitarist can be covered by algebra. E=IXR, P=IXE, etc.
     
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  14. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I must not have made myself clear. I was referring to getting the transistor biased to where it responds well. Germanium transistors are not manufactured to the same tolerances as their counterparts. It is much more important to get the resistor on the collector and the resistor on the emitter dialed in. The simple Germanium Giant circuit, mentioned above, chooses a 47K resistor for the collector and uses a 5K pot as a variable resistor on the emitter to dial in the bias. A similar silicon transistor circuit would not need the pot. Two resistors would be chosen and the bias would be close enough.

    The original post asks which caps and resistors to use with germanium transistors Imo, each Ge transistor must be dialed in. Once the resistances are found a resistor can replace the variable resistor but the next pedal you build will have a different Germanium transistor and it will require different resistors.

    The Germanium Giant has included two diodes for distortion. They can be removed for only a Germanium clean boost which would be very similar to the LPB-1. Tone controls can be added. Those ups and extras are up to you.
    The transistor doesn't need a heat sink for normal operation in the pedal. To avoid heat on the transistor, solder in a socket. Just plug the transistor in. No heat!;) Many times I break apart a socket for a Op Amp to use as a transistor socket.
     
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