Alek, QRO Technology made that same mistake with the fan speed switching on the 2500 amp. ?It eventually ruins the switch. ?In one case I had the warm up timer would reset every time the guy changed the fsn speed. ?To solve the problem I properly wired the system.
On Monday, December 30, 2024, 7:16 AM, mike repinski via groups.io <mikflathead@...> wrote:
I know that the W6PO amps I built for 2 meters and 220 mhz shorted out the resistor for operating bias. But he was a smart guy. :)? Some paperwork I have from? K9EK does the same thing.
In older commercial grounded grid amplifiers, it is common to see a
cahngeover relay used to switch between a zener diode or similar bias
regulator and a bias cut off resistor.
My question is, why did they do it like that?
To me, it is bad engineering, in that during the change of state between
transmit and receive, there is a short period where there is neither cut
off nor idle current bias applied. OK, it is a very short period but it
happens.
In my view, it is surely better to have the bias cut off resistor
permanently in series with the bias regulator and simply have the relay
contact short the resistor when the amplifier is keyed. That way, that
small period of open circuit bias can never occur. Why couldn't the
designers of these old amps see the simplicity and sense of doing this?
73, Alek VK6APK.
