I think bringing filaments up slow is a good idea. At one time we used a varister device in the degaussing circuit of the old TVs. These little round resistors would have about 100 ohms resistance when cold but would go down to a tenth of an ohm or less when hot. They make a very good auto starter for heaters. I use them in the primary of the filament XFMRs. But for long periods of setting a variac might be best.
73 John -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Tuesday, August 25, 2009 9:43 PM To: Discussion of AM Radio in the Amateur Service Subject: Re: [AMRadio] 100TH and 250TH advice and or comment 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: [email protected] > [mailto:[email protected]] 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 > > ______________________________________________________________ > Our Main Website: http://www.amfone.net > AMRadio mailing list > Searchable Archives: http://www.mail-archive.com/[email protected]/ > List Rules (must read!): http://w5ami.net/amradiofaq.html > List Home: http://mailman.qth.net/mailman/listinfo/amradio > Post: [email protected] > To unsubscribe, send an email to [email protected] with > the word unsubscribe in the message body. > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/[email protected]/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: [email protected] To unsubscribe, send an email to [email protected] with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/[email protected]/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: [email protected] To unsubscribe, send an email to [email protected] with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
