The AM Forum

Has anyone experimented with wideband impedance transformers using torrids to match the driver to the grid of a power tetrode (4 x .4, 4x1, etc)??   In the past I have used an LC network swamped with a non-inductive resistor in my old 4-400 deck for the grid matching network.....

PW

Look at the invader or ncl 2000. They did swamping. A BB step up will also work
but you will need a higher resistor value. I would load the tube side of the transformer.

LDG and SGC, MFJ sell 100 watt level autotuners that work great to drive amps. Use a 300 ohm resistor to swamp the grid of the driven tube, hook the tuner output to the resistor , hook the driver to the coax and step through the bands to let the tuner memorize the settings. You can use a cheap tranceiver as a vfo. LDG sells their tuner as an unboxed module expressly for this purpose. I have done it and it works FB.
DO NOT try to use a 50 or 100 ohm resistor as you will need way too much drive.
you can calculate drive by figuring the grid voltage that needs to be developed across a given resistor to drive your particular tube and work back from there. Most tetrodes willl like this system and be very stable. The bonus is no bandswitch.

Hi Skip,

Interesting post on the auto-tuners. Who is LDG and do you have a model number for their unboxed module???

Thanks & 73,

Bruce

What type of tube did you drive with the autotuner? With regards to the swamping resistor value did you try anything higher then 300 ohms?  It looks like the spec'ed  matching range for the module goes up to 600 ohms......

Joe