[ARC5] running ARC-5 receiever fillaments on AC.

[Bill Cromwell]

Hi,

The heaters don't require 24.0000000000 volts or 28.0000000 volts. A 
higher voltage DC input with enough headroom to regulate to 20 or 22 
volts (or somewhat less) will run the heaters just fine. Been there - 
done that. The *key* factor is the heater voltage (and heater current 
follows) does NOT change. The heaters operate at a steady temperature 
that is adequate for tube operation.

73,

Bill  KU8H

On 08/26/2017 10:04 PM, Brian wrote:
> Using a 24 Vac transformer is a very poor idea. You need to ensure that
> the regulator under full load does not see dips in the rectified DC from
> the raw rectified AC. You also need to allow for AC mains droops; the
> electricity supply authorities are permitted 10% droop in mains supply.
> Suggest at least 34 Vac nominal.
>
> Here’s the maths on your suggestion:
> 24 Vac rectified –> very rough 33.94 Vdc peak, less 10% supply droop –>
> 30.54 V peak, less two diode drops (FWB) at full load –> 29.14 V peak
> value. The average will be less. Doesn’t leave any headroom for the
> 7824. You can do the maths on 34 Vac.
>
> You’ll find the same design ‘philosophy’ used in very good quality
> telephone exchange battery supply and back-up systems. Where this design
> philosophy is ignored, eg, the exchange is run by an accountant, you
> will hear hum in telephone handset earpieces throughout the whole
> exchange area.
>
> And just a little point – no ARC-5, ATA, ARA, SCR-274N equipment uses
> tubes with filaments – all their tubes have HEATERS.
>
> 73 de Brian, VK2GCE.
>
> *On* Sunday, August 27, 2017 11:29 AM, you said:
>
> <snip>
>
> I'm going to rectify the 24VAC to 33.6 VDC  and pass that through a
> LM7824 to get back to 24V.
> That should keep the oscillators happy!
>

-- 
bark less - wag more