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High B+ in homebrew


 
6/3/2000 7:56 PM
DonJ
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High B+ in homebrew
Grettings, I have a question in my latest amp project I have a B+ of 654v before any other componets are installed the filter supply is conected and I'm getting 654v what should I do to bring B+ down to a usable level. Building 5f6a. thanks DonJ
 
6/3/2000 7:59 PM
DonJ
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One other thing I have seen MM amps with 700v with el34s whats the deal.
 
6/3/2000 9:43 PM
Peter S
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Don,  
EL34's are rated for 800volts on the plates. Music Man amps are class B amps....they run the screen much lower, also the Cathode to plate voltage is actually only around 550 or 600volts.  
As far as lower the B+.....you can use a zener to lower it maybe a 100 volts or so. I've never tried to get that much voltage drop with a zener, but maybe someone else on here has. You could hunt for a lower voltage tranny too.  
PS
 
6/3/2000 10:31 PM
DonJ
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Peter, Thanks for the reply. I'm kinda stuck with this PT when I measured the B+ when it was in the donor amp it was 525v,so I figured why not and made the cut in my nice chrome chassis. Maybe I will go ahead and finish wiring the amp and see what happens.Oh by the way the PT came out of a blown hammmond tone cab with 6 el84s and 4 12a_7s and 1 6au6 and 2 5u4g's all nos tubes. I figured it could handle 2 el34 and 3 12ax7s with 1 5u4g.would I hurt anything if I went ahead a finished this monster I'm using a new sensor 50watt ot and 5f6a circut. Tjhank you DonJ
 
6/4/2000 8:09 AM
Peter S
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You should be alright with that tranny.....after you get your other components in and your power tubes start drawing current, your voltage will drop quite a bit. You can also experiment with a few different rectifier tubes to get lower voltages. If your voltage is too still too high, get a reversed bias 50watt 50volt Zener Diode and the voltage will drop down about another 50volts or so.  
PS
 
6/4/2000 12:08 PM
Ray Ivers
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Don,  
 
Just a thought... a choke-input power supply would drop your voltage quite a bit; I calculate roughly in the neighborhood of 400 volts with the choke-input supply. This type of PS has good voltage regulation characteristics, so the 'sag' if any will have to come from the tube rectifier, not the PS itself. I don't know how a big choke is going to fit into your chassis layout scheme, though, and I've found they throw a pretty good hum field when carrying the entire amplifier B+ current.  
 
Ray Ivers  
R.A.G.E. Electronics
 
6/4/2000 12:39 PM
DonJ
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Ray,Come to think of it the hammond did have a pretty large choke lay down type.The only place I could fit it would be between the PT and OT. Maybe if I put a sheild plate between the choke and OT it would work? THanks, DonJ
 
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