DX-40/VF-1 chirp continued

[Steve Harrison]

At 07:55 PM 1/15/99 -0800, Jim Berry wrote:
>Hello Heath Fans,
>
>Right off the bat, I want to make mention that in my earlier post that I
>said to run the VF-1 off from say 200 volts.  It will work fine, but to
>really take advantage of the voltage regulator in the VF-1, it is probably
>better to run it from a supply of at least 400 to 600 volts.  You can do a
>little wiring changing in the VF-1 for it to operate at a lower voltage, but
>a higher voltage supply is probably actually easier to create.

I'd be a lil leery of this, because a resistor dropping 400 down to 150
volts at, say, 30 mils, will be dissipating... um... 7.5 watts. That will
probably put Heath's choice of temperature-compensating caps in the VFO to
a real test considering there's no ventilation holes in the VF-1!

>The separate power supply:  Got an old junker tube TV set chassis laying
>around?  It probably has everything you need to cobble up a separate power
>supply.  That is what I did.  Hung the parts all together with alligator
>clips.  Watch out.  This stuff can bite.  Be careful of any exposed high
>voltages.

Actually, if you're gonna do this, it might be easier to use the HV from
your transmitter and regulate it TWICE. For example, two external OA2s in
series to get 300V, then feed the VF-1. The first set will stabilize the
300V very nicely, probably making it nearly as stable as your line voltage
variation would with a supply feeding a single regulator.

And of course, it would save having to spend time making that other supply
:o) Further, you could experiment with different voltage regulators in the
"primary" regulator circuit. In addition, it would reduce the size of the
required dropping resistors since that total drop is now split between the
regulators. And you can mount that hot resistor OUTSIDE the VF-1.

A possible drawback is that you would have to set the current through the
"primary" regulators pretty high, close to 40 mils, to provide enough
excess to keep the secondary regulator alive plus run the VFO. In fact, you
could wind up having to separate the buffer amp B+ from the oscillator B+,
running them from separate regulators. But you could go real fancy and use
a dynamic regulator such as a 6L6 for the "primary" regulator :o) This
would be the ideal place to use that resistor with the adjustable tap that
you've been saving for "something" all these years. :o)

>...Heath used a 45 or 47K resistor across the VF-1
>output to create a load.  I grabbed my resistor substitution box and clipped
>the leads across the existing resistor.  As long as the subbed in resistors
>were between 50 and 5000 ohms the rasp went away.  I grabbed a 1000 ohm
>resistor and soldered it across the 47K.

So you can leave the 47K in there since it's effectively swamped by the 1K.
Possibly it was RF feedback; pickup from the DX40 even though you were
using a dummy load. I remember encountering something like that, I think it
was more drift and chirp when my 3L G4ZU minibeam (anybody remember those?)
was pointed overhead on 15m only, way back when.

>Last night I got everything all put back together in their respective
>cabinets.  Looking at this pile of dangerous open power supply.

You should have seen the "open-bench" I cobbled together to power my first
Galaxy V transceiver. A couple of weeks of that convinced my Dad that he
really outta spring his hard-earned money for a real Galaxy supply before
"the kid" electrocuted hisself...

>Have to come up with something to build it in.  Maybe tonight
>or sometime this weekend, I can get on the air with it.

If you can do the cascaded regulators thing, you could mount them on a
minibox at the back of the VF1. Place the box to the side at the back so
you can watch them as you key; almost as good as watching a pair of 866s!

73, Steve Ko0U/1

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