• Re: One step at a time. - tokyofist 16:44:29 04/15/06 (4)
  In Reply to: Re: One step at a time. posted by Victor_A on April 14, 2006 at 19:12:58:

  I desoldered the 5 diodes on the PS board. they all tested fine.

  I spent several hours going over every connection in the amp section, rewiring the filament wires, tube connections, ground connections, etc. the amp still hums - left channel is 2.3mV, right is 1.8mV.

  Peter - bear with me :) - i'm familiar with what feedback does, but i'm can't figure out which connections are part of the feedback loop just by tracing the circuit. could you be specificy which wires need to be disconnected? also, what is the heater center-tap?

  I had previously removed paint at the circuit ground and safety ground. There is continuity between the ground bus and chassis. Resistance between ground bus and safety ground pin of the IEC socket floats between 0-0.3 ohm.

  also, i'm confused by your reference to heater wiring on the PWB. are you referring to the filament wires?

  btw - in response to your questions from a while back: this is the P-P ella and with choke.
  
  

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  • Re: One step at a time. - PeterP 10:00:11 04/17/06 (1)
    In Reply to: Re: One step at a time. posted by tokyofist on April 15, 2006 at 16:44:29:

    I haven't abandoned you. My home computer has a virus so I'm using a laptop on a different network.

    The feedback that I'm referring to is the small gauge wires connected to the output transformer or output terminals. IIRC there is an RC across the output terminals and feedback is the wire that goes from the output to the input stage. (Since I haven't seen one, in the P-P Ella, it could be either from the output transformer or the output terminals.)

    As for biasing up the heater voltage, don't worry about that for now. Let's get it working stock first.

    I'll be back. ;^)

    Take care.

    Pete.
    
    
    

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    • Re: One step at a time. - tokyofist 18:50:38 04/18/06 (0)
      In Reply to: Re: One step at a time. posted by PeterP on April 17, 2006 at 10:00:11:

      With inputs shorted and feedback disconnected, the hum is audibly louder. In fact, with just the inputs shorted, hum is also louder than with inputs connected.
      
      

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  • Re: One step at a time. - Victor_A 02:55:00 04/16/06 (1)
    In Reply to: Re: One step at a time. posted by tokyofist on April 15, 2006 at 16:44:29:

    Are the Power Supply filter capacitors OK ? I am almost sure, that the problem is in the power supply. (B+)
    
    

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    • Re: One step at a time. - tokyofist 06:32:08 04/16/06 (0)
      In Reply to: Re: One step at a time. posted by Victor_A on April 16, 2006 at 02:55:00:

      Unfortunately, I don't have equipment to properly test them. Upon visual inspection, none are bulging and I don't see any signs of leakage. On the PS PCB, the smallest caps (on the far righthand side) measure ~12Kohm across the leads. The larger two pairs of caps measure in the megaohms.
      
      

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