|[AMRadio] Valiant Problems|
Freeberg, Scott (STP)
Scott.Freeberg at guidant.com
Fri Jun 11 10:08:21 EDT 2004
I think I know what the problem is. My Valiant started blowing the LV fuse too, often just sitting there. The problem was due to the 18K current limit resistor feeding the OA2 in the VFO case. I forget the R number. The 18K resistor power was under rated. Over time the hot resistor changed value, lower of course. As the resistance dropped, more current was supplied to the OA2. More current meant more power dissipation. For a while I put in large fuses but all that did was make it worse until the resistor reached 150 ohms, burned out the OA2, burned out the 6AU6 VFO tube.
Eventually it reached a point where it was blowing fuses all the time, that resistor had changed value from 18K to 150 ohms.
After asking a bunch of questions to various lists, I found it this is a known problem with Rangers and Valiants. I think the resistor was a 2 watt part. I replaced it with either a 4 or 5 watt resistor, and moved it out of the VFO compartment. I added a two position terminal strip under the VFO, ran the wires down through a convenient grommet, soldered the resistor to the terminal strip. That at least kept the 18K resistor heat out of the VFO compartment.
After that it worked like a champ.
I'd say this is your problem. Let us know how it turns out!
73, Scott WA9WFA
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