[ARC5] Filament Question - in RT-66

[Scott Johnson]

The battery tubes use an oxide coated filament, which operates around
1000-1100K, whereas a thoriated tungsten filament operates closer to 2000K.

Scott W7SVJ



-----Original Message-----
From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On
Behalf Of WA5CAB at cs.com
Sent: Saturday, October 03, 2015 1:59 PM
To: arc5 at mailman.qth.net
Subject: Re: [ARC5] Filament Question - in RT-66

No. Even the old LeClanche D-Cell can deliver several amperes for an hour. 
It's been at least 20 years since I last looked at the spec charts and I
forget what the rating was at the one hour rate. And none of the Signal
Corps catalogs (SIG 5, et al) that I have list an Anp-Hr rating, only the
voltage, size and contact type. But the original dry battery pack for the
RT-70 consisted of five BA-403/U in series for 7.5 volts when mounted in
CY-590/GRC. 
The BA-403/U is rectangular and physically about the size of four D-Cells.
In the CY-590, there is a 1.2 ohm resistor in the lead that eventually goes
to the three series-parallel filament strings in the RT-70. The resistor
would provide some current limit. But the filament and cathode design in the
battery tubes is generally such that there is no huge cold in-rush current
as there is with for example a 450-TH. As someone already pointed out, the
operating temperature of the heaters is much lower than for example standard
6.3 volt heaters. The operating temperature is barely up to a dull red. 

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

In a message dated 10/03/2015 14:07:55 PM Central Daylight Time,
kd5byb at gmail.com writes: 
> On 10/3/2015 11:13 AM, Kenneth G. Gordon wrote:
> >In the case of battery tubes, such as those Wayne is involved with, 
> >the answer is, generally, inrush surge does not occur.
> 
> Afternoon all,
> 
> Something that occurred to me. With battery power, is it possible that 
> the dry-cell batteries themselves limit the surge current? Or, better 
> said, they simply cannot provide a high inrush surge so it isn't a 
> problem?
> 
> thanks much and 73,
> ben, kd5byb
 
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