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previous: nuke The Zener diode is not a "Weber" mo... -- 10/7/2000 3:21 AM View Thread

Re: zener diode part #

10/7/2000 3:48 AM
Steve A.
Re: zener diode part #
    Thanks for your support of the semiconductor industry...   ;)    
    It seems to me that off-the-shelf PT's are available only with specific secondary voltages and adding in a zener to the PT CT or FWB ground connection is a great way to dial in the exact B+ voltage you want on the plates... And even if you custom order trannies from Hammond the voltage they produce could be considerably off-spec (ask Benjamin about that one!)  
    I haven't used the stud mount zeners yet, but I have been experimenting with the 9.1v/5W zeners that Bruce Collins told us about. (You can get them for about 50 cents each from Mouser.) With the currents normally seen in a 50W to 100W guitar amp, the 5W rating should handle any voltage drop up to maybe 12V just fine.  
    With them being so cheap you can experiment until you find the voltage that sounds best with your power amp. And you can wire up a noiseless switch to select between different B+ voltages (dealing with the lower voltages in the CT/ground circuit rather than the high B+ voltages). The transformer windings seem to act like a choke in squelching any noises when I toggle the zeners in and out of the circuit... [Maybe R.G. can shed some light on why these switches work so well- no pops, no clicks, nothing but the silent switching of the B+ voltages!]  
    IMHO power supply resistors work fine in dropping voltages to the screens, and to the preamp and PI tubes... but not for the plates of the power tubes. Ohm's Law rules here... (the voltage drop across the resistor will vary with the current drawn).  
Steve Ahola

Benjamin Fargen Steve,Hey there!!!<... -- 10/7/2000 5:07 AM