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Tube preamp con?

Discussion in 'Amps and Cabs [BG]' started by The_Lucek, Dec 23, 2013.

  1. The_Lucek


    May 21, 2011
    So here is the deal. I recently got a sm pro audio tb101 tube preamp. But it's missing its power supply. So it got me thinking, since i have a 15 watt all tube and my father warned me that i don't mes around with it since there is very high current running trough it, how come the tube preamp only needs 17 volts ac? That isn't that high, so i checked the tube (12ax7) spec and it says that only 6,5v is needed for the heater. But there are other elements like the cathode and the rest...
    I know the preamp is not great but for less then 15 dolars it's gona do... :D
    If someone could take the time to brake this down for me, i'd be very thankful. :confused:
    I know there are tube pedals but there job is just to color the sound while in a preamp it needs to amplify the signal...

    Sorry, i forgot the point... xD
    My point is: if the pre needs 17v, does that mean that the tube in it is used just to color the tone(as in most of pedals) or is it used to amplify the actual signal (witch is in my definition of a tube preamp, when the tube does the amplifying)
    sorry one more...
  2. Selta


    Feb 6, 2002
    Pacific Northwet
    Total fanboi of: Fractal Audio, AudiKinesis Cabs, Dingwall basses
    Output tubes easily and commonly exceed 600 V. Also, keep in mind (always) that voltage is not what kills you...
  3. Tube amps have transformers and capacitors. Transformers can increase voltages and capacitors can store those voltages. If I am not mistaken , my SVT has capacitors holding up to 600 volts and if you touch both leads to it , you get zapped by the whole 600 volts. It's not the tubes but the transformers and capacitors that will get you in the amps and your footswitch has neither. I am not a tech and my knowledge of electronics is VERY limited. I am sure there are people in TB far better qualified to explain the exact workings of this but I hope this will give you at least some insight into what your father told you.
  4. The power supply is AC output, this will allow a step-up transformer or SMPS for the plate voltage needed by the tube. While a 12AX7/7025/ECC83/ECC803 type will operate at much lower DC voltage, 180 to 300VDC provides the best "sound". Current needs of that "family" of tubes is pretty small so not all that hard to achieve that voltage from 17VAC (remember full tube amps can get 600+ VDC from 120 VAC).
    If the sound is not all that spectacular the plate voltage could be as low as 80VDC. It only has to have an output voltage of between 0.775 to 1.41VAC to operate as a full preamp.