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previous: DCH Thanks guys --The c... -- 7/20/2000 9:28 AM View Thread

Re: Lightning clone finished: ouch, high voltages!

7/21/2000 2:09 AM
Steve A.
Re: Lightning clone finished: ouch, high voltages!
    After rereading Bruce's original post, you ought to try the Sovtek 5Y3 first... especially since they are in current production and are presumably inexpensive. (I hate it when the only solution is an exotic NOS tube, which is not the case here! ;)    )  
    But to answer your questions, the zeners are polarized and you would mount them with the cathode band going towards chassis ground. They will generate heat so try to keep the body at least an inch off the circuit board.  
    The NTE # for the 9.1v/5W zener is 5124A; I believe that the ECG # would be the same. Mouse sells them in bulk with the 1Nxxxx number (look in the index under "zeners"). If you are going to buy the NTE/ECG ones, you might want to get the 5125A's (which are 10.0v) since Mouser does not sell that voltage in bulk.  
    As for the actual voltage drop, in the negative leg of a FWB the voltage drop seems to match up with the zener voltage. I'm not sure if it would be the same with a non-bridge power supply.  
    I'm amazed at how quiet the switching is... but keep the leads short or they can contribute hum. And with the low voltages involved these could be hooked up to a relay (e.g., you could raise the amp's B+ when switching to the Clean channel or drop it when switching to the OD channel). You would have to check the bias voltage/current at each setting and maybe use one pole of the added relay to adjust the bias...  
    Thanks again to Bruce for telling us about these great little zeners! (If you do the math you can see that 5 watts is much more than enough for a 10v voltage drop in any amp up to 100w; SVT-ers need not apply!) The only drawback I see to these zeners (or any zeners) is that you *are* losing power from your PT; if you were to drop your B+ from 400vdc to 300vdc, I figure that you would be wasting 25% of the capacity of your PT... and radiating that wasted power as heat inside your chassis.  
--Good luck!  
Steve Ahola

DCH Thanks Steve,That's... -- 7/21/2000 9:05 AM