From: phil_a@tpg.com.au   
      
   "Robert Kowalczyk"   
   > "Eike Lantzsch, ZP6CGE"   
   >>>  I have a transformer with 5V 4A winding, does it adequate for   
   >>>  2 x 5R4 since each 5R4 is 5V 2A?   
   >   
   >> The question is not so much if the amperage is OK but if the   
   >> transformer's isolation is good enough to stand the high voltage of the   
   >> B+ present on the rectifier's filament (direct heating). Ordinary   
   >> transformers for low voltage are not designed for this application. If,   
   >> however your transformer was meant to supply the heaters of rectifier   
   >> tubes, than you can assume that 300-400V are OK. Well - "assume" does   
   >> not mean that you can be sure.   
   >   
   >   
   > Where do you get this information from? Manufacturers data?   
      
      
   ** Transformers for use in tube amplifiers need a higher standard of   
   insulation to cope with the DC and AC voltages involved.  Unless a maker   
   states that a transformer is  INTENDED  for such use it is unwise to assume   
   it is OK.   
      
      
   > And what is the safe limit to use such transformers for directly heated   
   > rectifiers?   
      
   ** Depends on the particular transformer, how it is constructed and what the   
   maker says.   
      
   Eg  if the tranny is of " split bobbin" construction with the primary and   
   secondary wound on separate halves, then it may well be is capable of   
   withstanding 500 volts DC or more between those windings.   
      
      
   ....   Phil   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)