[ARC5] Filament Question

[WA5CAB at cs.com]

I would say no.  In the first place, running the Transmit-only tubes all 
the time would raise the internal temperature of the radio.  How much would 
depend upon whether you are using a 6, 12 or 24 volt supply.  Second, unless 
you are running it as a beacon or an AFSK station, the transmit duty cycle is 
typically very low.  Third, the current surge at turn-on is negligible 
because the tube filaments are supplied through current regulator tubes.  
Fourth, we will all be long dead before the supply of those tubes goes away.  
Fifth, if'n it ain't broke, don't fix it.  :-)

All original installations of the RT-70 run off of some type of battery.  
The only sets to later have an AC supply built for them were the RT-66, 67 
and 68 (primarily the latter).  And very few of those supplies were built, for 
the Gator Navy early in the Vietnam War. 

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480 

In a message dated 10/02/2015 21:28:18 PM Central Daylight Time, 
releazer at earthlink.net writes: 
> 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