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previous: Ray Ivers Rick,Amen on the bias suppl... -- 8/15/2003 3:46 PM View Thread

Re: Bias Supply Design

8/17/2003 8:01 AM
Greg Simon
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Re: Bias Supply Design
So Ray, on that Marshall you mentioned would the answer be to have better P/S regulation? Or what else would solve the bias issue?  
Reason I ask is that I have a project amp I have been working on for quite awhile which is a real doosy, and I think I may have the same issue where the bias voltage follows the plate voltage up and down. The amp is a 3 power amp in one chassis Conn organ amp from the 60's. No preamps on that chassis, though I am adding a seperate chassis with its own filament transformer and 3 preamps, one for each power section. So in the end, what I hope to accomplish is to have one head, with three amps in it, located in two seperate chassis. The head is as big as an SVT head!  
I'm towards the end of the layout stage for the preamp chassis at the moment, and once I get it built, I will tweak the power amp chassis to suit.  
 
The first section will be a 2x6L6 BF AA864/AB763 Bassman circuit with the Princeton bias modulating trem on the power tubes and fixed bias.  
 
The 2nd section will be a 2x7868, cathode bias, in the power amp with a see-saw inverter of some sort (the one which was already in there) w/ EF86 + cathode follower + 2nd gain stage + Vox tone stack in the preamp.  
 
The third will be a 2204 with 2 EL34's, fixed bias, with internal channel switching using JFETS and PNP transistors and some minor stage tweaking.  
 
When I've tested the power amps in the past, since they are all cathode bias, everything seems ok as I turn one section on or another off. But I wonder if it will still be ok when I set up two of them as fixed bias? The power supply is a voltage doubler, and I can't change that without changing the power supply transformer. Its putting about 445 volts on the plates with every section on, and goes up to 505 with all in standby.  
Thanks for any help on this you can offer!  
Greg

 
Replies:
Ray Ivers Greg,I think the answer in ... -- 8/17/2003 1:13 PM