Amplifier QSK modification

Here's a picure of the original T/R relay.


I replaced the old relay with a pair of Jennings RJ-1A vacuum relays.  These relays are rated at 5 kV peak and will handle 18A, and, most importantly, switch in 5 ms.  I bought these from Alan Bond of Max-Gain Systems .  He threw in a mounting bracket for free.  The relays were mounted on the bracket using several drops of RTV.  This serves to provide vibrational isolation of the relays from the bracket and the rest of the amplifier structure so that it won't resonate and amplify the switching noise, and also provides the relays with some flexibility to move when switching.  The bracket and relays were mounted to an interior wall of the amplifier using a couple of stand-offs I had in my junkbox.

Here's a picture of the new relays.


Notice that the coax is not connected directly to the relay pins.  They are connected using some thin copper stips.  The relay pins are fragile and the stress of a direct connection might crack the seal and ruin the vacuum in the relay.

Here's a picture of the RF compartment of the amp with the relays.



Every project has its 'oops' and this one is no exception.  Look at the picture below and see if you can find something wrong.


Ok, its a little tough to see.  To the right is the output of the tank circuit.  The two torriods are part of the tank circuit and provide the needed inductance on the lower bands.  The RF choke goes to ground in order to insure that the output stays at DC ground potential.  When I first wired everything up, I thought I had reconnected the choke to ground.  Well, I hadn't.  When I fired the amp up, I heard a loud ffzzzzzzzttttt sound and smelled something burning.  Well the burning was the outer insulation on the coax due to arcing.  The black smudge on the torroid on the left above is melted PVC from the coax.  Once I properly soldered the RF choke to ground, everything worked fine.