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

Fri May 6 01:20:05 EDT 2022

According to the RCA tube book two tubes can be run in parallel with a 100 ohm resistor in series with each tube. [new one to me]

I don't imagine that would make a very good regulator.

 A 6L6 or similar used along with an 0A2 would be a better way. [but more complicated] Jim

> On 05/05/2022 6:01 PM Dave Sublette <k4to.dave at gmail.com> wrote:
> 
>  
> Good evening,  I have left the VF-1 running for the past 5 to 6 hours with
> a very stable and accurate frequency counter connected.  I can tell you
> that the frequency has varied less that +/- 200 Hz in that time.  However
> the case is off.  I will repeat this after I get the case installed
> sometime in the future.
> 
> I find it interesting to note that this is the same VF-1 I asked for advice
> about a few weeks ago.  At that time I asked if it would be better to
> convert the VF-1 to solid state(which would eliminate the heat/drift
> problem) or try to keep it original.  The advice was unanimous to keep it
> original.
> 
> However, now I find several suggestions that I remove the OA2 circuit in
> order to minimize drift.  I only have two questions.  What drift?  I
> haven't seen any (but expect to when I get it into the case).  But, what
> happened to the overwhelming sentiment for keeping the unit in original
> configuration?  I can't have it both ways.
> 
> Now I don't really expect an answer.  I just find it interesting to think
> about what has transpired.
> 
> I really do enjoy this group and have learned a lot.  I am not a
> "Boatanchor" guy per se.  But I was given this unit recently from the
> estate of a dear friend who died in an auto accident a couple of months
> ago.  It has only sentimental value for me as it was built by him and used
> as one of his first rigs way back when. I also have his DX60, which I have
> refurbished and have on the air.  I use the rig as part of the Novice Rig
> group activities on Monday night.  It has been a rewarding experience.
> 
> Thank you all again for your help.
> 
> 73,
> 
> Dave, K4TO
> 
> On Thu, May 5, 2022 at 7:37 PM JAMES HANLON <knjhanlon at msn.com> wrote:
> 
> > 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
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