[ARC5] 3A5 Filament Voltage Question

[Bill Cromwell]

On 08/04/2013 04:46 AM, Leslie Smith wrote:
>    John,
>    I looked at 3 data-sheets for the 3V4 type "tube".
>    The last sheet referred to  type 3V4WA, by Tung Sol.
>    It described the 3V4WA as "a ruggedized version of the 3V4, making it
>    suitable for military operations".
>    I know you understand the significance of "W" suffix in the valve type
>    designation.
>    The datasheet gave a method to test the ability of the "tube" to
>    withstand vibration.
>
>    The datasheet says this about the filament:  "Absolute maximum rating
>    of the filament voltage (Ef) shall be 1.25 +/- 20% VDC.
>    Interestingly it does not give a rating for the series connected
>    filament.  Only mentions 1.25 volts in THREE places.
>    So (you can do the maths!) 1.25/5 equ 0.25 volts, giving a working
>    voltage of 1.0 to 1.5 volts.
>
>    If you want to see the datasheets I have, pls let me know.
>    On the other hand, if you don't want to see them, don't tell me, and I
>    won't send them.
>
>
>    73 de Les Smith
>    vk2bcu at operamail.com
>
>
Hi Les,

Thanks for that information. I have run the bejeepers out of the 
'battery' tubes on the 1.5 volt D cells (and even AAA occasionally) and 
those cells do come up a little over 1.5 volts when new. With the 
information you have provided I will start using the NiMH cells with 
their slightly lower voltage and better economy to keep everything well 
within the spec sheet range - just in case. I would like copies of the 
spec sheets, Les. If you found them on the web a URL will work for me.

I see those tubes as best suited for portable or 'emergency' power 
operation when the utilities are down...and of course for QRP ham 
operation. Some of the battery tubes with 90 volt plate supplies (or 
more) can push about a watt out of an antenna terminal. If I use them in 
AC powered equipment the series diode regulator looks like a very good 
choice.

73,

Bill  KU8H

Michigan QRP Club M-1778

4 States QRP Club 555