Tube Amplifiers
Sierra78 asked:

I have a guitar amplifier that I 'm. that modding. 1 electronic valve has 6j5. I have another tube 6j5 that Im not using. If both tubes fixed paralelamente the total power of removal of the dual amplifier? i seen the adoption, I did not know that I could overload the transformer exit. A final questiom two 6j5 paralelamente unbalance the circuit?


4 Comments so far

  1. Peter H on September 25, 2009 7:49 pm

    You would need to change the cathode resistor and you have a very good chance of burning out the output transformer.

  2. goober on September 26, 2009 11:41 am

    You may overload the output transformer if it is the output tube. Sometimes two are used in a push pull arrangement so adding only one will unbalance the output for distorted sound quality too.

  3. Brian T on September 29, 2009 1:39 pm

    I assume the 6J5 is a misprint because it is a very low output tube. If it is in an output circuit circuit, putting it in parallel will change the output impedance and your output transformer will no longer be matched. Bad matching to an output transformer will produce distortion and at best, a lower output of power. At worst, it will burn out the tubes. Please understand the differance between clean distortion due to overdriving and just plane distortion because of circuit limitations. 30 years ago, a transister amp designer won a A vs. B test (tube vs. transistor) because the tube people like the distortion from their amps. He added a one ohm resistor in his speaker lead (upsetting the impedance and the feedback) and came up with the same “warm” sound the tube people liked!

  4. Numbat on October 1, 2009 12:51 pm

    World of difference between designing in another tube and modifying an existing piece of equipment.

    First question raised is your power supply capable of the increased power? Additional power always has to come from the power supply.

    Then you have to ask if there is room for the additional tube. Power tubes always need good air circulation and putting an additional tube next to the existing one might ruin natural air flow around the original. Possible consequences might include melting envelopes and much angst and loss of reliability. Class A amplifiers are very inefficient at the best of times. This means they produce huge amounts of heat for very little power output.

    Let’s consider what you may gain, if you do put the tube in. You might get twice the power (after a total rebuild). This amounts to a sound level increase of 3dB, an amount you will only just be able to discern.

    Maybe ditch the amp and look for something with real grunt?

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