[Boatanchors] More on the VF-1 and parallel VR tubes

[JAMES HANLON]

First about the VF-1 ... That 5K dropping resistor and for that matter the OA2 also will get pretty warm and may contribute to some drift in the VF-1 if they are in theVF-1 cabinet.  You might be better off to put them in the power supply and just run a regulated 150 volt line to the vfo.  The Viking 122 vfo has its dropping resistor inside the vfo cabinet and it is more drifty than it needs to be because of that.

As to VR's in parallel, I actually did do that successfully in two applications starting back around 1952.

First off, my brother and I were running a BC457 Command Set as a vfo for our transmitter, and we needed a source of regulated 300 volts at something more than 40 ma for the oscillator plate and final screen voltages.  We used four OD3/VR-150s in series-parallel with balancing resistors to get around the current-hogging problem, and ran that power supply and rig until about 1960.

Also, our final amp was a pair of push-pull 809s which require grid bias of 75 volts and ran 50 ma of grid current in CW, 62 ma in phone.  We got our grid bias supply by putting two 0A3/VR-75s in parallel (with balancing resistors) with an electrolytic filter capacitor connected across them to ground in series with the grid-return lead.  At the first application of grid drive (when we tuned up or just went on the air with existing adjustments), the grid current would flow through the VRs and ignite them and the capacitor would charge up to 75 volts.  Removing drive would extinguish the VRs but leave the capacitor charged to the 75 volts necessary to keep the final in cut-off with no drive.  So we got along without having to build a separate bias supply.  Again, that ran happily for a good eight years with no trouble.

So it can be done.

By the way, in 1960 my brother had graduated from college and I was about to do the same, so we divided up our station gear.  I took our HRO-50, and brother Bob took everything else.  I think I got the better end of the deal!  I'm still using the HRO with some additions further along the way like a product detector, SSB AVC, mechanical filters, and regulated filament voltage on the local oscillator, mixer, and bfo.  It is close to my best receiver and certainly still is my favorite.

Jim, W8KGI