Honestly i find the scope of these articles just a bit too wide and am having to parse them down to certain sections in order to learn what i need to. Here are some links to the articles i've been looking through in case anyone else wants to read up on this stuff. ![]() I have been spinning my head around reading through a bunch of stuff, and i think some things are starting to stick. A pi-network to match a 50-ohm transmitter to the four tubes is not a big deal. A solid-state radio won't be so happy about this. A tweak of the radio's Tune and Load controls would take care of this. In the era a tube-type radios this was no big deal. No ham transceivers with a solid-state final yet in 1968. The original article's date of 1968 is a clue. This will result in a high SWR between the radio and amplifier when it is keyed and amplifying. The input is feeding the cathodes of the four tubes in parallel directly, with no impedance-matching network. Keying the 'ground' side of the tube circuit puts a lower voltage across the contact points when they open up, and reduces the size of the arc in a big way. Keying the "high" side of the power supply puts more stress on the relay contacts as a rule. Wears out the tubes prematurely, and makes the amplifier efficient at only one thing, heating the room. You don't want them drawing idle current all the time. That's another way to shut the tubes down in receive. Typical way to do that would be to break the ground connection to RFC5 through a third normally-open circuit of the antenna relay.Īnd maybe the power supply diagram shows a relay that shuts off the 900 Volts in receive mode. ![]() What it really needs is a way to cut off the tubes' anode current while receiving. Using the same negative voltage to power the antenna relay just simplifies the thing. Makes the max voltage from the pot half the negative 25-Volt source. The 10k pot for each grid is fed from a 10k fixed resistor. The tubes will typically need 8 or 10 Volts of negative bias. The power supply schemo will presumably show the heater voltage being rectified to obtain negative 25 Volts DC.
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