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Hello MEF, long time no see. I am trying to add a VVR to my Fender Champ. I'd like to bring down the entire B+ line. I have a few questions about implementing this. The first question is, what makes this VVR circuit different from this one? The first circuit uses an additional NPN transistor and I'm not quite sure it's purpose.
My second concern is choosing a MOSFET. It seems that most inexpensive MOSFETS don't handle operating in the linear region well. Their thermal characteristics aren't as "good" as the more expensive variety. Dana Hall VVR kits include the beefy NTE2973 which is out of production and expensive. However, I've seen cheaper alternatives suggested on the internet such as IRF740 or IRF830. Is this truly just a matter of heat disappation? If so, I feel that with sufficient heat sinking the cheaper TO-220 package FETs could be used. But I wonder if there's more to the equation.
Finally, I've read conflicting reports of where to place the VVR circuit; before or after first filter cap? Some say the VVR operates better being fed the pulsing non-filtered DC while others say the exact opposite that it should be steady filter DC.
Any opinions or suggestions, feel free to chime in. Thanks!
My second concern is choosing a MOSFET. It seems that most inexpensive MOSFETS don't handle operating in the linear region well. Their thermal characteristics aren't as "good" as the more expensive variety. Dana Hall VVR kits include the beefy NTE2973 which is out of production and expensive. However, I've seen cheaper alternatives suggested on the internet such as IRF740 or IRF830. Is this truly just a matter of heat disappation? If so, I feel that with sufficient heat sinking the cheaper TO-220 package FETs could be used. But I wonder if there's more to the equation.
Finally, I've read conflicting reports of where to place the VVR circuit; before or after first filter cap? Some say the VVR operates better being fed the pulsing non-filtered DC while others say the exact opposite that it should be steady filter DC.
Any opinions or suggestions, feel free to chime in. Thanks!