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Tweed bias tweak


 
1/27/2000 6:28 PM
Chuck
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Tweed bias tweak
Hi, '59 Tremolux is running hot:  
37-40 ma idle current. 2 NOS RCA 6V6GT's, NOS  
Syl. 5U4GB rectifier. What would be the best way  
to bring this down? Would tweaking the bias supply  
resistors ie: changing the 56k to 68k or so  
work? Is there a way to lower the plate voltage with  
a different rectifier?  
Thanks in advance for any advice,  
Chuck
 
1/27/2000 9:22 PM
John Stokes
Yep. You'll have to tweak the values of the fixed resistors in the bias supply to get yourself a little more negative voltage on those control grids. I installed a trimpot in mine.  
 
 
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1/27/2000 9:32 PM
Chuck
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John, thanks. Did you replace one of the resistors with  
the pot or place it in series with the resistor.  
Thanks again,  
Chuck
 
1/28/2000 5:47 AM
John Stokes
I placed it in series.
 
1/28/2000 5:10 PM
Matthew Springer
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More general bias pot questions
I've been wondering about these tweed bias pots I hear so much about. What value does one usually use? Also, do you just use two terminals kinda like a variable resistor? What sort of Wattage rating? Linear or Log?  
 
Inquiring minds want to know.
 
1/28/2000 11:06 PM
Chuck
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Hello Inquiring Minds, I haven't done this yet  
but I would try using a trimpot in a rheostat type  
fashion: tie the wiper to one end of the pot and  
put the two ends in series with the resistor that  
you want to raise the value of. I guess it depends  
on the values of the bias supply's resistors as to  
what value of pot would be best to use. On the 5G9  
Tremolux (56K & 82K) I would put a 25K pot in series  
with the 56K resistor.  
 
1/28/2000 11:10 PM
Chuck
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Oh yeah, at least 1/2W, linear.
 
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