[ARC5] Filament Question

[Scott Johnson]

I would guess that the recued lifetime, if it is attributable to the filament opening, would be due to the fact that the filament is much more fragile when at temperature.  This was one reason that Amperex developed the "harp " filament in many of their instant on mobile tubes, the harp structure kept the filament stands in constant tension over temperature, so that shock and vibration were less of a factor.  I also think that the limited lifetime problem is more acute in the transmitting types, as the emission current density is much higher than it is in a receiving type.  All that being said, I think I would still baby my 1L6's!

Scott W7SVJ

-----Original Message-----
From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On Behalf Of Glen Zook
Sent: Saturday, October 03, 2015 9:47 AM
To: kgordon2006 at frontier.com; Leslie Smith; ARC-5 List
Subject: Re: [ARC5] Filament Question

I don't have any real experience with the radios and battery tubes referenced.  However, in the past, I have had a lot of experience with the "instant on" tubes used in the commercial two-way radio arena.
The RCA "Super-Carfone" units used the instant on tubes in the driver and final stages of the transmitter.  There was a button, in the center of the hang-up button on the microphone which operated a relay to turn on the filaments when the microphone was removed from the hanger or, in some installations, the hang up box operated the relay when the microphone was removed.
By the time the microphone was removed from its "hung up" position until the operator got the microphone in position to speak, the filaments were at full emission and the transmitter was putting out full power.  Then, when the microphone was returned to the hanger / hang up box, the filaments were turned off.
Sometimes, the operator would not replace the microphone in the hanger / hang up box for any number of reasons.  This applied voltage to the "instant on" tube filaments for an extended length of time.  That, in turn, resulted in the burning out of the tube filaments in a relatively short period of time.  In vehicles, where the operator generally did not place the microphone in the proper place, especially the final amplifier tubes, an "instant on" version of the 6146, would burn out in less than a month.  When the microphone was used properly, the normal life span of these tubes was, in general, between 2-years and 4-years.
Motorola had a similar radio that was used extensively for motorcycle installations.  Some of those radios had entirely tube-type transmitters and the later versions used tubes in the driver and final amplifier stages.  Most of these radios used the 2E24 which is an "instant on" version of the 2E26.  The filaments were turned on by a hang up box.  Again, when the microphone was not "hung up", the life span of, especially, the 2E24 was reduced substantially.
I don't know for sure.  However, my experience with "instant on" tubes in the two-way arena, leads me to expect a similar fate for the referenced radios. Glen, K9STH
 Website: http://k9sth.net
      From: Kenneth G. Gordon <kgordon2006 at frontier.com> 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

  
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