The AM Forum

Well, it seems when the 1200 pf coupling capacitor shorted, it vaporized one of the coupling switch contacts. I know these are completely unobtainable (but if you have one from a junker you'd part with, let me know), so I am looking at trying to repair it. I've been reading the discussions on the forum on how to do this, drilling out the rivets and securing the new contact with tiny hardware, but really, is this a feasible task? I have a completely brand new bandswitch for the Valiant with contacts the correct size, but I am reluctant to sacrifice it, since I might need it some day if the original craps out. All the other ceramic switches I have use smaller contacts. Is there a source for new switch contacts?

I love the old girl, but she sure is showing her age.

Doug

Doug,

You might also consider doing some measuring to see if you could fit a multiple section variable capacitor with "receiver" plate spacing into the space occupied by the current coarse switch and fine variable capacitor like Heathkit did when they switched from the DX-100 to the DX-100B.  I doubt if many (any?) of us are using the wide range matching capability designed into the Valiant output network and into 50-75 ohms the voltage developed across the loading capacitor is minimal so a closely spaced capacitor can be used.  This would avoid future issues with the switch contacts and fixed capacitors.

My Valiant 1 and 2 rigs are still fine but at some point this might become a reasonable fix instead of dealing with switch contacts and replacement caps.

OK, coupling switch repaired. Sorry for the poor quality photos, my phone doesn't want to focus so close. Anyway, you can see in the first photo the vaporized switch contact. The other one shows the repair. Hardest part was finding a tiny enough screw and nut in my junk box.

Next problem is no audio. Static modulator current rises very slowly to 60 ma when transmitter is keyed. The value is right, but why does it rise slowly to that value? And, of course, no audio out. I'll find it, but any clues anyone has will be appreciated.

Doug

Looks kind of close to that nut...

It does look a little close, but the voltages in the loading circuit should not be very high.  Hard to tell exactly from the pics.

Fred

It's the angle of the photo. There is plenty of clearance and no arcing. Hard to get a straight on image with all the wiring in the way.

Doug

Doug in some situations you can have pretty high voltage on that switch.  It can arc to several points pretty easy with that situation.

I'll put some insulation on the nut. Don't see what else to do, since it's the stock configuration for that switch. I never hot switch the coupling caps, but an arc could have been what took out the original contact.

But I'll leave that for another day. Right now I am wrestling with a direct short of the 300V line to ground. L44 gets very hot and the 1.5A fuse blows. Now, this only occurs when the thing is sitting upright. Turn it up on its side to get to things and the short disappears. Nothing is protruding below the bottom of the cabinet. Replace the fuse, check all the wiring, fire it up, and it works great. Turn everything off, wrestle the brat back into its upright position, hit the switch and pfftt!, pops the fuse. Grrrrr.

Doug

OK, found the short. Slight sag in wiring harness, nick in a wire's insulation, on level surface wire shorts to chassis, on its side it doesn't.  Glad I didn't have to unlace the entire wiring harness to find it. But I am out of 1.5 A fuses, had to put a 2a in there until tomorrow. Should be OK for now.

Doug