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Re: Best way to reduce Filament voltage?


 
11/21/2003 2:11 PM
Major Pain Re: Best way to reduce Filament voltage?
Thanks R.G. I read the info and seen the schem and thats really cool way to reduce the hammond trannie primary input back to the required 115vac.  
Im gonna see if I can get a 8vac @3 amp trannie and do this setup.  
Thanks again  
 
M.P.
 
11/23/2003 3:11 PM
Shea
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How about a pilot light?
I've used a 6.3v / 250 ma pilot lamp for this purpose. It usually doesn't bring the voltage all the way down to 6.3v, but it does keep it under 7.  
 
Shea
 
11/23/2003 8:03 PM
Magamps
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Re: Best way to reduce Filament voltage?
How about if I come up with a "vintage" voltage regulator circuit using germanium transistors? You'll need a 12Vrms filament winding but I can get it to 6.3 V  
Mike
 
11/24/2003 10:36 PM
Shea
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Can you make one with a selenium rectifier?  
 
Shea
 
11/25/2003 6:07 PM
Magamps
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Where are you going to find selenium these days? Cougar Electronics I guess???  
Mike
 
12/2/2003 4:51 AM
Major Pain Re: Thanks to all who posted
I wanted to say thanks to all who posted, I wound up using the resistor method that Don Symes suggested and it worked very well. Ive got exactly 6.3 vac on the tube filiments now and the amp sounds excellent too.  
 
I still cannot understand why hammond power trannies set up their primaries at 117vac instead of a 120 or 124vac like here in the USA.  
 
Seems Hammond trannies are so well built but the lower pri voltage is a pain when trying to set up a new build. I guess im missing something here for their reason but just thought I would voice my 2 cents about it.  
 
Thanks again every one as the suggestions were all excellent.  
 
M.P.
 
12/4/2003 8:28 PM
hasserl
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MP good to see that you got this corrected. I was just dealing with the opposite problem, too little voltage. One of the things that was causing my problem is the circuit rectifies the current to dc thru a couple of diodes which drop 1.4 volts out of it. That combined with an apparently underrated PT leaves me with 4.07 volts at the last tube in the circuit (pre-amp tube #1). This was a commercial pcb amp, not a homebrew. I've found that certain tubes will run okay at these low volts, and some won't. But this is another way you could correct your overvoltage problem while at the same time providing dc to the filaments for reduced hum.  
 
Just an idea that might come in handy later.
 
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