[AMRadio] 100TH and 250TH advice and or comment

crawfish at surfmore.net crawfish at surfmore.net
Tue Aug 25 22:43:19 EDT 2009

John Mohn was W5MEU. I remember him talking about that one night over 20
years ago.I have an old 450TL that I want to use. I guess I need to bring
it up slowly with a variac feeding the filament transformer to keep the
inrush current from wrecking the filament, or is that an issue?
                                                   Joe W4AAB

> I think there is at least some truth to this Lee, but I am not sure of
> why.  By the same token though I have run 250ths for quite some time and
> with many hours of no use both winter and summer without air conditioning.
>  They seem to always work the same even though I may only fire them up
> once or twice a year (much to my dismay).  So I really don't have any good
> answer for this.  If all the tubes in question were assemble into the 610
> at the same time then maybe you could just pass this off as "it was
> finally time that the air leak got to them".  Don, K4KYV and Tim, WA1HLR
> have discussed this sort of thing quite a bit as well as deterioration of
> cathode coatings in both directly heated tubes and indirectly heated
> tubes.  You may want to consult with them about this.  One thing is for
> certain, if the final tube is weak then it will be very difficult to get
> it to produce a wave form output that matches the audio wave form, and it
> gets worse as the power demand goes up.
> 73
> John
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of LEE BAHR
> Sent: Tuesday, August 25, 2009 2:20 PM
> To: Discussion of AM Radio in the Amateur Service
> Subject: Re: [AMRadio] 100TH and 250TH advice and or comment
> John Moan (forgot his call and spelling) (SK) in San Antonio used to run a
> few BC-610s.  He always rotated his 100TH and 250TH tubes to keep gassing
> from forming in them.  He had about a dozen BC-610s and around 17 R-390A
> receivers in his shack.   I think he used to say it was bad to lie them on
> their side too.  He seemed to know what he was doing and swore the cycling
> of the tubes was neccessary to keep them alive.  He claimed storing these
> tubes would kill them in time.  I am only talking about 100TH and 250TH
> tubes.
> Lee
> w0vt
> Houston
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