Orange drop for ceramic disc.

Discussion in 'Shock Brother's DIY Amps' started by heave1, Jun 18, 2021.

  1. heave1

    heave1 TDPRI Member

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    Is it safe and effective to replace the .02uf ceramic discs on a Princeton Reverb with Orange Drops of the same values and voltage?
     
  2. heave1

    heave1 TDPRI Member

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    Since the caps that control tremolo modulation aren't in the signal path at all, they just alter the bias of the first output tube or control the optocoupler pulsation, would replacing the ceramic disc with orange drops make any difference?
     
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  3. NTC

    NTC Tele-Holic

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    It is safe to substitute the same capacitor value with the same or higher voltage using different types. Since the amp tone won't be affected by different cap types In the oscillator circuit, there will be no change in tone. I would use the ceramic there because it is cheaper, but if you have the orange drop on hand, go for it.
     
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  4. Boreas

    Boreas Friend of Leo's Silver Supporter

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    As long as the values are identical, it will be OK to switch them. Will it make any difference? As long as the caps MEASURE the same, it shouldn't be an obvious difference, if any. Just keep in mind each cap has its own tolerances.
     
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  5. Drew617

    Drew617 Tele-Holic Silver Supporter

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    Yep, have done this a few times. Ceramics discs are visually and vintage correct, and cheaper in the absolute sense. In practice they're not, though, because I've got piles of 715P, 716P and M150s on hand and would rather not do the same for discs. My ears are only bronze, not golden, but I've never perceived any difference between caps of like value in a tremolo circuit.
     
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  6. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I theorize, yes they can make a difference... but my firm answer is maybe...

    I have read no evidence to support my theory but I theorize the microphonic properties of ceramic disc capacitors does *help* the tube start to oscillate.

    The circuit is designed for the tube to oscillate. Sometimes we have to wait for the effect because it is slow to start. The tube will not oscillate at all if it is not given any, for lack of a better word, *signal* to start the oscillation and, ime, it is slow to start because it is not given a strong enough signal. Other more knowledgeable shock brothers may correct me here but it is not apparent which component in the circuit generates the *signal* to start the oscillation.

    These caps form a local feedback and are directly connected to the control grid. They are in a good position to start the oscillation. This is not to say the caps are the only components that can start the oscillation. They are not.

    I welcome any observations that would disprove my theory.

    (I use the term *signal* loosely in this instance because the control grid is not necessarily the starting point to begin the oscillation.)

    Edit: Thanks @NTC . I edited the post. Increasing the cathode cap value can also help when it is slow to start. The point of the theory is that something has to start the oscillation. It can come from the B+, a noise from the tube, the vibrato pedal switch, these caps, or a combination of any of these places.
     
    Last edited: Jun 18, 2021
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  7. NTC

    NTC Tele-Holic

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    The number of RC stages actually creates POSITIVE feedback - that is why an oscillator works and is why an amp squeals when the OT wires are connected wrong. Oscillations result because the circuit is unstable. If there isn't enough gain, the oscillator may not start. If by chance your oscillator is slow to start, you could increase the value of the plate load resistor bu one or two standard values to get things moving.
     
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