VF1 VFO and HG 10 VFO voltages

[Kenneth G. Gordon]

> I don't have my VFO manual with me in Colorado and
> don't know the voltages needed.
> 
> Can someone please tell me the voltages needed for the
> VF1 and HG 10 VFOs. The required current is also
> unknown. I want to construct several power supplies
> and need the voltage and current requirements. Your
> help will be greatly appreciated. Thanks and 73, John, K5PGW

According to the manual, the HG-10 requires 108 VDC at 25 mA, 
and 6.3 VAC or DC at 750 mA. for the circuit itself. However, the 
listed 108VDC is the internal regulated voltage, by a 0B2, not the 
input voltage via the interconnect cable.

So, if you were going to build an external power supply, the 
minumum DC voltage required would be about 150 VDC for the 
HG-10, and about 200 VDC for the VF-1, but this low voltage would 
require a dropping resistor change.

As far as DC voltages are concerned, both the VF-1 and the HG-10 
can handle a not inconsiderable range of input voltages, provided 
you make the proper changes internally.

DC currents required for both VFOs are not more than 50 mA., 
exclusive of filament.

Both VFOs have a VR tube that delivers the required stabilized DC 
voltages to the oscillator tube, a 0A2 (150 VDC) in the VF-1 and a 
0B2 (108VDC) in the HG-10.

There is a large power droppiing resistor in each VFO that drops 
whatever input voltage you choose to use, to the proper level to 
feed the VR tube.

In the HG-10, as I remember it, you have two choices of that 
resistor value, chooseable by a jumper: i.e. remove the jumper for 
one voltage range and install it for the other.

In the VF-1, if your choice of input voltage lies within the range 
mentioned by another user, that dropping resistor value does not 
need to change. However, if your choice of voltage is much above 
or below that specified, the resistor must be changed also.

In any case, the LOWEST voltage you can use must be around 
20% above the VR tube rating in order to ensure reliable starting.

Then an appropriate dropping resistor must be used to insure that 
the maximum current that the UNLOADED VR tube passes is not 
above its maximum, either 30 or 40 mA depending on the tube you 
are using. The miniature VR tubes (OA2, etc) are rated at 30 mA 
max. Some of the octal versions are rated at 40 mA.

However, in the interests of ensuring that the VR tube lasts a 
reasonably long time, one should set the current through them to 
the MINIMUM that will ensure that it stays lit under load.

Ken Gordon W7EKB

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