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Data for Drake 784-213 output transformer available?


 :
9/7/2005 2:49 AM
anon Data for Drake 784-213 output transformer available?
Hi,  
where can I get the primary impedance and inductance for a Drake 784-213 output transformer?  
 
The impedances of the secondaries were  
labeled 3.75, 7.75 and 15 Ohms.  
 
The trannie has the same size as the Drake's in  
Marshall 50W amps (labeled 784-139).  
 
The Drake Web Site doesn't contain any info and I  
guess the folks working there are too busy to  
care for historical data.
 
9/7/2005 8:09 AM
Dai Hirokawa

try Marstran:  
 
http://marstran.8k.com/
 
9/8/2005 2:50 AM
anon
Dai,  
 
thanks for the link!  
On Marstran.com I found  
 
" This OT is from a Carlsbro amp and is used with EL34 tubes. " Carlsbro is an english company.  
 
Meanwhile I measured the primary inductance and impedance of the Drake 784-213:  
 
Lprim ~ 20 Henry  
Zprim ~ 4.3k (assuming 4,8 and 16 Ohms secondaries)  
 
From EL34 datasheets I know that for B+ around 375V  
the Zprim is usually 3.4k, but for those circuits  
with B+ close to 500V Zprim is 4k.  
 
On the other side the 6L6GC fixed bias push pull  
primaries are 5.6k in data sheets, but transformers  
offered for Fender and Boogie amps come along  
with 4.4k to 5k primaries.  
 
Does anybody have experience with the change in  
tone of EL34's with 4.3k / 4.4k primaries - or  
simply speeaking Fender style OTs - in comparison  
with 3.4k primaries?
 

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