Toxic wattmeters.
Maybe I should call them carnivorous wattmeters. They'll eat your amplifier.
Here's the problem. We have seen it with both Dosy and PDC meters. The cabinet panels are first punched, then painted.
Next they mount the coax sockets into the holes, secured by two rivets each.
Just one problem. No actual metal-to-metal contact between the body of the coax sockets and the metal underneath that paint layer.
Oops. Newer Dosy meters have a tooth washer under one corner of the coax sockets. If it penetrates the paint, you get a tiny bit of metal-to-metal ground circuit this way.
Until you fire up some real RF power. The tiny contact area gets hot and oxidizes. The ground connection to the panel metal degrades.
Oops.
Here's the prodedure we adopted to keep these meters from blowing up our customers' amplifiers.
First you need to tin the edge of each coax socket with solder.
Should probably do it a little better than this. The versions that have three output sockets with a switch will be a bit clumsy to reach, but you get the idea.
The pc board gets taken loose, and a notch cut into the edge, into the ground foil that runs along it. You'll need to scrape the mask paint around the notch, so you can solder to it.
A length of coax braid long enough to reach all the coax sockets gets fed through the notch in the pc board, and lap-soldered to the input-side coax socket. This pic doesn't show it, but you need to solder the braid to the ground foil on the edge of the pc board.
The long end of the braid now gets lap-soldered to the edge of the three output sockets on the version with the antenna switch.
Run it to all three output sockets, same deal.
If you want to be fanatical, drill out the rivets on the coax sockets and scrape the paint around the holes in the panel. This method is a bit more expedient. We scrape the screw holes for the pc board on the rear, and use tooth washers under the board's two mount screws. Seems to ground the whole thing well enough and with a lot less labor.
No customer has come back with a blown-up amplifier after his meter gets this treatment.
Seems to work well enough.
73
Maybe I should call them carnivorous wattmeters. They'll eat your amplifier.
Here's the problem. We have seen it with both Dosy and PDC meters. The cabinet panels are first punched, then painted.
Next they mount the coax sockets into the holes, secured by two rivets each.
Just one problem. No actual metal-to-metal contact between the body of the coax sockets and the metal underneath that paint layer.
Oops. Newer Dosy meters have a tooth washer under one corner of the coax sockets. If it penetrates the paint, you get a tiny bit of metal-to-metal ground circuit this way.
Until you fire up some real RF power. The tiny contact area gets hot and oxidizes. The ground connection to the panel metal degrades.
Oops.
Here's the prodedure we adopted to keep these meters from blowing up our customers' amplifiers.
First you need to tin the edge of each coax socket with solder.
Should probably do it a little better than this. The versions that have three output sockets with a switch will be a bit clumsy to reach, but you get the idea.
The pc board gets taken loose, and a notch cut into the edge, into the ground foil that runs along it. You'll need to scrape the mask paint around the notch, so you can solder to it.
A length of coax braid long enough to reach all the coax sockets gets fed through the notch in the pc board, and lap-soldered to the input-side coax socket. This pic doesn't show it, but you need to solder the braid to the ground foil on the edge of the pc board.
The long end of the braid now gets lap-soldered to the edge of the three output sockets on the version with the antenna switch.
Run it to all three output sockets, same deal.
If you want to be fanatical, drill out the rivets on the coax sockets and scrape the paint around the holes in the panel. This method is a bit more expedient. We scrape the screw holes for the pc board on the rear, and use tooth washers under the board's two mount screws. Seems to ground the whole thing well enough and with a lot less labor.
No customer has come back with a blown-up amplifier after his meter gets this treatment.
Seems to work well enough.
73
