[ARC5] Filament Question

[Bill Cromwell]

Hi Wayne,

The battery tube filaments were designed to be switched off and on as 
well as to minmize power consumption/increase battery life. I have begun 
playing with them here. You will be hard pressed to even see the light 
from the filaments - they don't get bright red or orange. There is much 
less heat inside the radios.

It just seems intuitive that cycling them on and off would shorten 
filament life (and tube life along with it) but the thermal shock isn't 
going to be nearly that it is in a *regular* tube. Flashlight bulbs 
(draw more current than those filaments) don't seem to fail from thermal 
shock very often but maybe they get dropped before that can happen <evil 
grin>.

I have a big pile of pentodes and I am going to experiment with turning 
off the tube filaments for "standby". When I get some useful information 
I'll post. The project includes a transmitter (around about 1 watt)  and 
a receiver - not a transceiver.

A broken tube might have something to do with the transmit audio problem 
<evil grin>. I hope the repair is as simple as installing a replacement 
tube.

73,

Bill  KU8H


On 10/02/2015 10:27 PM, Robert Eleazer wrote:
> I have recently gotten interested in firing up my RT-70/GRC, mainly because I started testing the tubes in it with my tube tester in attempt to identify the cause of missing transmit audio.  By the way, the first clue I found when I took the set out of its case was a broken 3Q4.....
>
> The RT-70 was designed to be powered by batteries in the PRC-16 version and so I guess that is why the tubes are DC powered instant heating filaments that cycle on and off depending on transmit and receive.
>
> Would it be better for the longevity of those tubes to rewire the filaments so that they are ON at all times when the set is powered up from the AC power supply I built for it?
>
> Thanks,
>
> Wayne
>