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Valiant, HUM on carrier.




 
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Author Topic: Valiant, HUM on carrier.  (Read 4329 times)
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Ed/KB1HYS
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« 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 Wink
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73 de Ed/KB1HYS
Happiness is Hot Tubes, Cold 807's, and warm room filling AM Sound.
 "I've spent three quarters of my life trying to figure out how to do a $50 job for $.50, the rest I spent trying to come up with the $0.50" - D. Gingery
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« Reply #1 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.
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Rodger WQ9E
Steve - K4HX
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« Reply #2 on: February 02, 2011, 11:50:28 AM »

Easy to check. Remove the clamp tube and fire it up.
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k3zrf
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« Reply #3 on: February 02, 2011, 12:31:16 PM »

and park that clamp tube in the spares box
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dave/zrf
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« Reply #4 on: February 02, 2011, 12:41:07 PM »

Spare screens R cheap enough  Grin

and park that clamp tube in the spares box
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