HF-81 Resistance Measurements

Discussion in 'Eico Place' started by Flip69, Oct 7, 2018.

  1. Flip69

    Flip69 Member

    I am troubleshooting an HF-81. Among other things, I am making a chart of the resistance measurements at each pin for each tube. I am taking the measurements according to the guidance provided in the Eico manual and on the Sam's Schematic. I have a couple of questions.

    How do you take the measurements for pins 3, 4, and 5 of V11 and V12? Are they taken to chassis ground? I ask because the measurements I am getting are not what I expected. The Sam's Schematic says the resistance will vary based on the condition of the electrolytics. The Eico manual says the resistance should be 100k. When I take the measurement, the resistance starts high, somewhere in the 10M to 18M range, then slowly decreases. I have watched it count down to as low as about 4M, then the auto stop/off on my DMM turns the DMM off, so I do not know how low it will ultimately go. When I turn the DMM back on, I either get a reading of 0, or the reading starts high and begins counting down again. What is happening here?

    Also, there is nothing connected to pin 1 on V7, V8, V9, and V10 (V9, V10, V4, and V5 respectively on the Sam's Schematic). When I measure resistance at that pin, I get a reading of 0 on all four tubes. Both the Eico manual and the Sam's Schematic says the reading should be 340k. What gives?


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