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Author Topic: Tone Change in HD-10  (Read 903 times)
W0SQD
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Posts: 2




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« on: July 26, 2010, 08:25:48 AM »

I acquired a Heathkit HD-10 electronic keyer in e-bay.  The tone of the keying monitor is too high for my liking.  How do I lower the pitch to a more comfortable level?
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KQ6Q
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« Reply #1 on: July 26, 2010, 02:30:10 PM »

there should be an internal adjustment - look for a pot labeled 'sidetone pitch' on the circuit board.
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KA5N
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« Reply #2 on: July 26, 2010, 03:37:53 PM »

The HD-10 has no tone control.  The audio tone is generated by a multivibrator.  There are .02 ufd capacitors connected between the collector of one transistor and the base of the other transistor
(Q9 and Q10).  You can lower the tone by paralleling additional capacitors until you get a more pleasant tone.  Start with something close to .02 ufd .  This should lower the tone quite a bit.
You can calculate the frequency using the time constant formula and determine what the charge time is for the capacitor/resistor pair.  Alternatively you could substitute variable resistors for the fixed resistors in the circuit (47K ohms) higher values give lower tones.
Good Luck
Allen
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W0SQD
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« Reply #3 on: July 26, 2010, 08:56:23 PM »

Thanks for the information.  It looks good to me.  Been a ham since 1954, but have been off the air for the past 20 years.  I am 82 and feel like a novice Shocked)
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