The AM Forum

Greetings...

I finally got time to fire up my Valiant for the first time since it was purchased. Unfortunately I ran into problems. It tunes up on all bands just fine with 130-150w output on CW. For whatever reason, I get no output in the AM position (no plate current, no idling current, etc). I do get some upward movement of the meter in the MOD position. I checked to see if the jumper plug was installed, and indeed it is.  All tube filaments are lit, and I do have low & high voltage. Just no modulation in the AM position as described above.  My first thought was a bad or open modulation transformer... Not sure what I'd do if that was the case...  I'm open for any suggestions as to something I might have missed.  Thanks for reading.

Best regards,

Gary, K7EK

Gary,

With the Valiant disconnected from the AC outlet, pull the accessory plug from the back and measure the resistance between socket terminals 2 and 3 with the mode switch in the AM position.  You should find a low resistance (less than 100 ohms); if this indicates open or high resistance then either there is a wiring problem or the modulation transformer secondary is open.  If you find an open then it is time to pull the chassis and measure at the modulation transformer secondary wiring to see if the transformer or wiring/switching is the problem.

If you find normal resistance, double check your accessory plug to make sure that all required jumpers are in place.

Hopefully it is a switch/wiring problem and not an open modulation transformer secondary.

Let me add to what Rodger alread said. I would also attempt to try it with a 'fresh' plug if one is available. The reason for this is I had an issue with my Ranger, (same plug) where only certain filament would light up. The socket for the plug would not make proper contact with the connectors. Consequently I had to hard wire the filaments so they would work. Don't believe everything you see.