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Title: Valiant, HUM on carrier. Post by: Ed/KB1HYS on February 02, 2011, 10:31:29 AM I've noticed a pronounced hum on the Valiant. Show's up in both CW and AM mode, so it' related to the RF deck.
Oddly, on the scope it appears as a square wave modulation of the carrier, the carrier envelop has a fairly flat edge, then a drop of about 3-5% then a sharp rise back to carrier level. The low points are 3-5 times smaller than the high points, not sinusoidal at all. I would have expected that a HV filter issue would show up as a 60 or 120hz sinusoid... so I'm thinking there is an issue with the clamp tube causing it to modulating the carrier. More as it happens, and thank God I never put ALL the screws back into the case on that beast ;) Title: Re: Valiant, HUM on carrier. Post by: WQ9E on February 02, 2011, 11:31:21 AM Ed,
The clamp and keyer tubes are both a common cause of hum in the Ranger/Valiant/500. Also try it on crystal to rule out the VFO. Note that heater/cathode leakage in the keyer tube is likely to be more pronounced with VFO than crystal so don't let this mislead you into tearing into the VFO before trying a sub for the keyer tube. Title: Re: Valiant, HUM on carrier. Post by: Steve - K4HX on February 02, 2011, 11:50:28 AM Easy to check. Remove the clamp tube and fire it up.
Title: Re: Valiant, HUM on carrier. Post by: k3zrf on February 02, 2011, 12:31:16 PM and park that clamp tube in the spares box
Title: Re: Valiant, HUM on carrier. Post by: W2VW on February 02, 2011, 12:41:07 PM Spare screens R cheap enough ;D AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
and park that clamp tube in the spares box |