[ARC5] Receiver Voltages.

[Ian Wilson]

I would guess that a pair of 7k wirewound resistors of several watts
power handling were (compared to a dropper resistor/VR tube):
  a) cheaper
  b) had essentially infinite lifetime
  c) far more rugged

VR tubes can be seen in use as plate regulators in the Collins 51J
(look at the supply to the PTO) and in numerous other tube
receivers, once LO stability became an issue.

A resistor + VR tube would offer power supply rejection owing to
the low dynamic resistance of the VR tube. The small-signal
equivalent circuit of this is a potentiometer with the upper arm
being the resistor, and the lower arm being the VR tube.

73, ian K3IMW


On Fri, May 1, 2015 at 9:33 AM, Mike Feher <n4fs at eozinc.com> wrote:

> Gas filled tubes indeed generate noise, and, in fact not all that long ago
> were still used as microwave noise sources for measuring noise figure.
> However, the noise is far from white. White noise is really just a
> mathematical term since it implies a constant power noise density at all
> frequencies which we cannot generate in real life. The term "Pink" is often
> referred to as bandlimited noise. I am sure you all wanted to know this,
> HI.
> 73 - Mike
>
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
>
>
> -----Original Message-----
> From: ARC5 [mailto:arc5-bounces at mailman.qth.net] On Behalf Of Dennis
> Monticelli
> Sent: Friday, May 01, 2015 12:02 AM
> To: Brian
> Cc: ARC-5 Maillist; AKLDGUY .
> Subject: Re: [ARC5] Receiver Voltages.
>
> Brian,
>
> Not wishing to argue, but gas filled breakdown tubes of all types generate
> some white noise, not just neon.  Yet VR tubes are commonly used for screen
> or plate regulation.  What little noise exists can be bypassed by a cap.
> At least the breakdown tube has some power supply noise rejection; a
> resistor divider has none.  As for light, it's a pretty small effect and
> how
> much light gets into the underside of an ARC-5 type receiver anyway.
>
> I think Dave came up with the best reason for using R's.  You can run the
> set more easily at low voltages if the screen is allowed to track down with
> a sick B+ line.
>
> Dennis AE6C
>
> On Thu, Apr 30, 2015 at 7:18 PM, Brian <brianclarke01 at optusnet.com.au>
> wrote:
>
> > Hello Dennis,
> > Neon discharge tubes were available and being used as quasi Voltage
> > regulators around the time of Dr Drake's design of what have become
> > known as Command receivers.
> > However, neon tubes radiate noise, while resistors do not. Where would
> > you suggest such a neon stack reside in order to provide regulation of
> > the screen Voltage without raising the noise floor?
> > The firing Voltage of neon tubes also depends on ambient light. Where
> > neon tubes were used as Voltage regulators, eg, the LM series of
> > heterodyne frequency meters, they were inside a completely covering
> > metal box and noise was largely irrelevant.
> > So, I reckon Dr Drake's design team's solution was appropriate for the
> > application.
> > 73 de Brian, VK2GCE.
> >
> >
> > On Friday, May 01, 2015 12:39 AM , Dennis said:
> >
> > I hear you, Neil, but it still seems excessive to me.  The screen
> > current is very small and the bouncing of the supply voltage creates
> > far more variation (via the divider) than the screen currents
> > themselves.  Besides, a simple neon bulb stack could provide better
> regulation at a fraction of
> > the current.   At 250V, that resistor chain pulls 18mA and dissipates
> 4.5W.
> >  I respect the original designers, but this is still somewhat of a
> > mystery to me.  I'm sure they had a good reason.
> >
> > Dennis AE6C
> >
> >
> >
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