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Full wave bridge rectifier: easy way to lower B+


 
2/24/2000 8:48 PM
Carlos Full wave bridge rectifier: easy way to lower B+
Hi!  
 
My plexi clone has got a full wave bridge rectifier. Is there an easy and cheap way to lower B+?  
 
 
Regards  
 
Carlos
 
2/24/2000 11:07 PM
Bruce
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How far do you need to drop the B+?  
A few 9.1v to 12v 5W zener diodes installed between the grounded part of the FWB rectifer will drop the over all B+ down.  
Bruce
 
 
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2/25/2000 11:42 AM
GFR
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I don't know how much you want to lower it so...  
 
Look at the Fender "the twin" (red knob) amp schematic on Steve Ahola's site.  
 
You just need a DPDT switch and a couple of resistors. Easy and cheap. With this circuit you lower B+ to HALF (giving you 1/4 of the output power).  
 
If you don't need something so radical, both Randall Aiken and RG have circuits for lowering B+ on their sites. You'll need a zener, a transistor (bipolar or MOSFET), a couple of resistors and problably a heatsink for the transistor.
 
2/25/2000 3:44 PM
Carlos
I'd like to lower it from about 430V to 380V. Randall wrote to me that his circuit doesn't work for a bridge rectifier.  
 
CU  
 
Carlos
 
2/25/2000 6:43 PM
Bruce
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I don't know what "his circuit" means, but if you mean the 2N3055 and zener, I can't tell you 'cause I never tried it with a FWB.  
The thing does work with a FW rectifier however.  
Bruce  
 
 
2/25/2000 9:24 PM
Carl B. Maybe this might work. What do you Think, Guys?
Guys,  
 
Could you comment on the following?  
 
The way to drop that voltage without wasting power might be with a stiff cap or inductor between the "top" HV winding and the bridge.  
 
The choke or the cap wouldn't waste (much) power since neither has not much in the way of relavent resistance loss.  
 
The cap would have to be non-polarized (not a problem, just use two caps back-to-back with positives pointing out).  
 
Since the line frequency won't change (unless he goes to europe), the ratio of the Xl of the PT secondary to the Xc or Xl of the in-series element would be fixed.  
 
Aside from introducing more "sag," are there other implications to this approach? (I was just thinking, with an in-series cap you might have to watch the values for an unintended *boost* at Fzero! Haven't thought this all the way through.)  
 
- Carl B.
 
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