Since a long time I had an early version of the famous “Dierking” 2m amplifier (link) lying in my junkbox. Together with an NTR17 transformer (400-350-0-350-400 + 2×6,3) I assembled a nice and compact amplifier (20x20x15cm) for use with my FT290.
Since the NTR17 transformer does not provide extra voltages to easily generate -Vg1 I decided to “lift” the cathode with the use of a BD242C PNP power transistor and a zener diode. I needed 36V to get about 50mA quiescent current. Also, the Vg2 voltage is stabilized with a MJE310 high-voltage transistor and a zener at 270V. Va is 950V loaded.
The 6.3V provide the glow voltage for the tube, and in series with the other 6.3V, rectified and stabilized with a 7812 the DC is provide to the switching logic and the small 12V fan for forced cooling. My FT290 provides 6,8V on the antenna connector via a 4k8 resistor during transmit, and this voltage is used in the amplifier to switch the RF and the Vg2. For this a BC547 and a BD138 (pnp) are used. The output is switched with a small coax relais CX-1051, and the input RF and Vg2 are switched with a standard SDS S2 12V relais. Both relais are mounted directly on the N (output) and PL (input) connector. For details, see schematic. Error: of course plus and minus of rectified HV are taken from centers of the diode bridge. And the bleeder resistors (all 100k) are connected over each diode.
And how I’ve built it:
Here a picture of the amplifier in use, not fully enclosed yet.
In the picture you see an output of some 140W (!) , regretfully with a bad SWR from my Tonna antenna (1:2). Using a dummyload the SWR is perfect, the left needle stays down.