[ARC5] Receiver Voltages.

[Dennis Monticelli]

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
>
>
>