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Title: Valiant crapped out- Post by: N8LGU on August 12, 2005, 09:32:05 AM Last night my Valiant had no modulation after warm up. Worked ok before shutting
down the night before. Alll meter readings normal except only a very small kick upward when tapping the D-104. Hmmm... Mod idle bias is normal... Carrier and loading normal... Pull it out of the case... whew!... 12AX7 weak. Replaced it with a good one... Readings the same and still no audio. All other tubes check good... Ran the Mod bias up and down and got normal meter swing on the Mod currant... Have to go to work, now. Will keep you posted. Maybe my D-104 crapped out. Cant find my spare. I'll have to get out the Audio generator, Monday. Title: Re: Valiant crapped out- Post by: Glenn NY4NC on August 12, 2005, 09:50:03 AM Just a shot in the dark but I remember reading somewhere that the audio driver transformer is a common failure mode in these rigs... Check for an open secondary perhaps?
Last night my Valiant had no modulation after warm up. Worked ok before shutting down the night before. Alll meter readings normal except only a very small kick upward when tapping the D-104. Hmmm... Mod idle bias is normal... Carrier and loading normal... Pull it out of the case... whew!... 12AX7 weak. Replaced it with a good one... Readings the same and still no audio. All other tubes check good... Ran the Mod bias up and down and got normal meter swing on the Mod currant... Have to go to work, now. Will keep you posted. Maybe my D-104 crapped out. Cant find my spare. I'll have to get out the Audio generator, Monday. Title: Re: Valiant crapped out- Post by: N8LGU on August 13, 2005, 10:58:10 AM Thanks, Glenn. I'll check it out. I have one set aside for the transmitter I.m
building, but I don't want to use it on the Valiant. I wanted to keep the Valiant stock, but may go ahead and pull out the clipper and do Timtron's resistance coupled mod at this juncture. -Dave Title: Re: Valiant crapped out- Post by: N8LGU on August 22, 2005, 11:42:52 PM Rock Cave Dave's Valiant is back on the air. Turned out the choke L-45 went open. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
I removed the 6AL5 and 6C4 and bypassed all the clipper/ shaper circuitry. Also increased the audio coupling condensers (yes, CONDENSERS) to .087 uF . At least it was nothing serious. javascript:void(0); Cheesy |