XPost: sci.electronics.repair   
   From: legg@nospam.magma.ca   
      
   I'm working on a Harman Kardon FM100 "Counterpoint II" that shows   
   signifigant variations, internally, from the documentation provided by   
   SAM's HF3 repair and servicing manual, or other references searchable   
   on the web.   
      
   For a start, the valve pins are reversed, by section, in V1 and V2,   
   from the SAM's schematic. The tube sections are swapped - confusing,   
   but not a biggy. Second, the tube types differ from SAM's and all   
   other references.   
      
   1) V1 dual triode in the RF amp and mixer stage are the older   
   6AQ8/ECC81, rather than the later 6BK7A/ECC83 expected in the SAM's   
   schematic and listed in other web references.   
      
   2) V2 dual triode in the AFC and oscillator sections is 6AQ8/ECC81   
   rather than the 12AT7 expected in the SAM's schematic and web   
   references.   
      
   3) The printed circuit board has the correct heater connections for   
   the single 6V heater of 6AQ8, without any rework in evidence (pins 4/5   
   receive 6V normally - same as the other 6v heaters, pin9 is grounded).   
      
   4) Cathode resistor of the grounded grid 6AQ8 RF input amp is 91R, vs   
   the 68R expected. No note in SAM's about variations here.   
      
   5) Plate resistor in V2 oscillator is 6800R, vs the 1000R expected in   
   schematic. No SAM's note on variations here. This seems to be an   
   extreme circuit change.   
      
   The non-functioning mixer self-biases at half the schematic grid   
   voltage value and 2/3 the plate current - but  expect this when input   
   signal is missing Grid resistor is 20% low with age/dirt. Oscillator   
   grid resistor seems low in schematic at 22K, but what do I know.   
      
   As this is the section that seems to be malfunctioning, I'm wondering   
   if there's any advice related to the earliest versions of this tuner   
   that might ease in reviving it. Tubes test functional for heater,   
   emissions and transconductance, if a little slow to warm up.   
      
   RL   
      
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