Tuning Networkp

Tuning Network:

There's a voltage doubler circuit that's used to supply 12 volts to each of the two relays. One relay is used for transmit and receive switching. The other is used for band switching between 30 and 40 meter band. The band switching relay which you'll be able to see from the photos is mounted just under the plate tuning
capacitor. One of the 6.3v winding off the transformer is used to supply voltage to the doubler circuit. Voltage measurement were taken and I'm getting about 18vdc from this circuit with no load. Also the transmit led lamp and power on lamp and band switch indicator lamp are getting power from this circuit. Band switching is control by a rocket switch on the front panel along with a led lamp to let me know when the amp is in the 40 meter position.

I'm not using a tune input circuit. My Yaesu FT-950 has a built in antenna tuner in it so I'm using it to tune the input of the amplifier.

Before the band switching relay was wired up I did a check on the output tuning network and all check out as you'll be able to see from the photos with swr being measure 1:1. After some testing with a dummy load and on the air testing. It seem that I need to move the 30 meter band tap 1 turn. As I found out that the plate tuning capacitor was almost fully open. The tank coil and the loading capacitor came out of my SB-200 amp.

There's also a photo showing relays with both relay contact tabs solder together with a small piece of #14 wire. Relays are DPDT 12v at 10A.

I made mounting brackets for the plate tuning capacitor. Installed tank coil for the PI Network just off the side of the tuning and loading capacitor. The tank coil came out of my SB-200 amplifier.

Below you'll fine a image gallery of pictures of the PI Network. Click on the thumb nail picture on the right to scroll through the pictures.

Here's a black and white picture with Loading coil with taps for 30/40 meters. Coil was taken from a beat up SB200 Amp. Also there's a pic of the relay band switch, That allow me to switch between the two bands. You can also see the variable tuning capcatior which also came from the SB200

Another view of the loading coil and relay band switch. The variable load capacitor is also from the SB200 Amp.

View with all tuning capacitor and loading coil in place

Taps are setup for the 30 meter band with a good swr match, the same holds for the 40 meter band.

Here's a view of the relays with a solid peace of 14 gauge wire solder accoss each relay contact..

Here's the voltage doubler circuit that supplies power to the relays one is used for transmit keying the other is for the band switch relay