[TenTec] Grid Protection-425

[Art Trampler]

Greetings,

 

Since it doesn't seem that anyone has added a grid protection circuit to
their 425 (based on previous inquiry), is anyone interested in doing that,
maybe a few of us work out the circuit together and hopefully develop an
"elegant" solution?

 

I've gone over KK5DR's design for a relay to trigger a latching relay.that
perhaps might be used to interrupt the supply voltage to K5 on the Relay
Board? If that supply voltage is interrupted, then the amp would go into
standby, I believe, and RF from the exciter would bypass the amplification
circuits.

 

Right?

 

As for how to do this, KK5DR has a grid current sampling circuit off the
cathode B- line, which seems similar to the 425 Input Bias Board, with  B-
on 85 (?), sensed by R17 and sent to the Meter Switch Board from connection
83 to 72 (U1a).

 

Could that be the same place to take off to switch the transistors and
engage the relay in KK5DR's design? I imagine one could build it around the
output of U1b going high, to turn on the overdrive LED, but that would mean
the same threshold would be set both for the LED and tripping the grid
protection circuit. That may not be a bad thing, but one may want to have
the LED come on at a somewhat lower level of grid current.

 

If you've read this far you know I am not an electrical engineer nor an
amateur builder, so I'm talking this one out. I would appreciate it if
anyone else is interested that they get in touch with me and we see what we
can come up with. As an alternative, if someone wants to review this and
even charge for the design/instructions, based on what I've supplied and
something like the KK5DR design, let me know. I'd rather develop it with
someone but am most interested in adding this protection.

 

73,

Art K0RO