500W HF Amplifier

The amplifier make use of television sweep tubes 6P45C (Russian made) and no plate transformer power supply. Plate voltage is about 950 volts (220 x3 x 1.4) initially I thought about using x4 but kept getting tube "flashovers" so had to install the switch  (S5-1) to drop to x3.
The choice to use television sweep tubes is kind 'a poor one, but I had them already so not to throw them out, right? also I found the wonderful web site: "EL519, PL519, 6P45C Grounded Grid Amplifier" which gave me another push to make this amp.

The amplifier features:
 3 antenna switch,
 SWR meter,
 Soft start circuit,
 Cold tubes transmit protection,
 Two speed fan control with lower speed when receiving and higher when in transmit plus about 90 sec. delay after getting back to receive,
 Also the "remote tune" circuit for FT-857/897 radios (maybe some other radios also have this feature):
on  these radios there is ACC jack which you can use depending on jumper J27 position for tuning amplifier or antenna tuner (they call it TX REQ) or for keying an amplifier (TX INX) the same TXINH is routed on CAT/TUNER Mini DIN so you can take it from there and have them both. When pressing the switch "Low Power/Full Power" TX REQ is generated and also some negative ALC voltage through D6-4 is applied and because of that radio transmits with lower power, or just TX REQ when tuning with full power. It might be useful if amplifier is not located next to operators position.

My only regret about the design that for the control circuits I should have used a microcontroller probably "Arduino", this would have made schematic simpler and most importantly much more flexible.


There are some pictures of the amplifier:

73 Jonas N0LY/LY3QA

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