Valiant, HUM on carrier.

[Ed/KB1HYS]

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

[WQ9E]

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.

[Steve - K4HX]

Easy to check. Remove the clamp tube and fire it up.

[k3zrf]

and park that clamp tube in the spares box

[W2VW]

Spare screens R cheap enough 

and park that clamp tube in the spares box