[Milsurplus] Free - running osc at 7 MHz - more.

[Kenneth G. Gordon]

OK. I have done some more work with the original schematic.

As far as I am concerned, the circuit is an early version of the Hartley, but I will accept 
correction from anyone who knows better.

There are two "taps" on the total inductance: one to the grid, and another to the cathode. 
The cathode tap is "below" (nearest RF ground) the grid tap. The grid tap is directly 
connected to the "hot" end of the "antenna" coil. The "antenna" coil is actually the tank coil, 
and they call it the "antenna" coil, because the antenna is tapped directly onto that coil.

The antenna tap point MAY be adjustable, but I don't see anything on the schematic to 
indicate that.

The design is such that feedback is not easily varied by adjusting the inductances, so you 
have to use C-2 to get oscillations you want.

There is a 350 pfd cap, C-1, in parallel with the antenna tuning cap, C-3, 2 - 35 pfd.

If you wish, you may easily change the transmit frequency by either changing the value of 
C-1 (smaller values resulting in higher frequencies), adding a cap in series with C-1 (thus 
reducing total capacitance there), or by simply, as you suggested earlier, shorting out turns 
on L-4, the "antenna" inductor. All methods would work. I would think that shorting turns 
would be both easiest and less inclined to effect stability.

Due to the fact that you can't easily change the inductance of L-3, there is probably a limit to 
how far you can move the transmit frequency, but at least it should cover 40 meters from 5 
MHz. IMHO.

Set C-1 to minimum capacitance, plug a low-range RF ammeter into the jack "U" if you have 
one, or watch the milliammeter on your power supply, then key the transmitter and adjust 
C-1 until you see some RF current or a change in your power supply current.

At 400 V, you should see about 32 mA and about 13 watts input. Grid current will be about 6 
mA. The grid-leak resistor is 6.4 K, BTW and grid voltage should be about -39 V

Then find where you are transmitting and go from there.

I wish I had a rig like that. It sure is an interesting speciman of early radio.

I'll look at the receiver next.

Ken W7EKB