[ARC5] Filament Question

[Kenneth G. Gordon]

On 3 Oct 2015 at 14:53, Leslie Smith wrote:

>   Hello Wayne,
>   Lacking any specific knowledge about your question, my guess would be
>   a definite "yes".

I disagree for reasons I have previously stated.

>   I guess that thermal cycling would reduce the life of the filaments
>   and therefore the tubes.

I reply: that would depend on the tube in question. In this case, a "blanket" 
statement does no apply.

>   I suspect (from your question) you think the same as I do.
> 
>   In an editorial in "Ham Radio", the editor Jim Fisk, wrote about a
>   surplus receiver he had operated from the mid-40s.
>   I may be wrong in detail here, but as I recall his editorial, his set
>   was wired so the filaments were always on.
>   He switched the B+ line when the set wasn't in use.  He believed (as I
>   recall) that the thermal cycling of metal to glass (in the tube base)
>   was the main source of failure of tubes.  He pointed to the 30 year
>   life of his set, with the filaments constantly on, as evidence of his
>   hypothesis.

And I operated an RAL-7 receiver for over 12 years, only turning it off once 
to test the tubes. Finding nothing wrong with them, I turned it back on and 
left it on until I was able to aquire a more modern receiver...but in this case, 
the tubes, 6D6s and 41s, were 6.3 VAC filamented tubes which draw 
significant current when compared with battery tubes.

Wayne is talking about battery tubes with 1.5 V and 3.0 V filaments. The 
tubes are DESIGNED for "instant-on", are designed to "ramp up" internally, 
and IMHO, leaving them on would result in REDUCED life.

>   I don't know if he's right, or not, but his theory seems to have
>   reason on-side.

Well, yes, but not if he is dealing with battery tubes...which, btw, are, to me, 
a favorite category of tube.

Ken W7EKB