John, I don't get the 250TH to load worth a hoot! The plate voltage is fine. The drive checks out good back to the pair of 807s. I saw the evidence of the drive at the grid clip.
The 100THs had been set with the specified mA on the speech amp. I don't like the PA mA reading so I am hesitant to leave it on while I go hunt around the backside to look at all three plates. It has sat for over a year + now, as I have had shoulder surgery and trying to move it around even WITH a "moving man" dolly underneath is no simple task. [The wife has the whole area with wall to wall carpeting.]. There is bare concrete underneath that. Bob - N0DGN John Coleman wrote: > Do they show color on the plates or gas type ionization color when in use? > If they show gas ionization color when in use then they defiantly have air in > them and could be caused by overheating due to some malfunction. Maybe they > have many more hours on them than you know about. If the plates or just a > little red but no gas ionization then the tubes or probably OK. Make sure > the grid drive stays up at the recommended level and one way to tell if a > tube is losing its conduction is to check the grid drive. If the grid drive > falls off considerably when the plate supply is energized then the tube is > getting weak. A small amount of grid current fall is normal. The > neutralization must be very good to make this check else capacitive feedback > will affect your findings. I have used 250ths for some time and have never > seen them loose vacuum from any normal use. I did crack one once taking the > grid connector off. That was a little heartbreak. Especially when Geoff > W5OMR was te > lling me to be careful. HIHI > 73 > John, WA5BXO > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of rbethman > Sent: Tuesday, August 25, 2009 11:07 AM > To: AM Radio List > Subject: [AMRadio] 100TH and 250TH advice and or comment > > Question: > > I have noticed that the 100THs and 250THS that are in their original > boxes, either not used at all, or maybe use for less than an hour to > test them, seem to be doing fine. > > Their envelopes are crystal clear an can not see any sort of defect. > > Then the ones that are in one of the two BC-610s that has the hours on > it, even though it last performed flawlessly, now appears to have gone > gassy with some milky white inside the envelope. > > Is this perhaps due to over heating or maybe I should phrase this as the > convection cooling of these radios since they do NOT have fans. > > Ideas? Comments? > > It has always been metered and watched with a scope for observing > waveforms, and the wattmeter is the newer Model Bird with peak reading > built-in. (However true they really are!) > > Bob - N0DGN > > > ______________________________________________________________ > 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 > > -- +------------------------------------------------------------------+ | AM Amateur Radio Operator NØDGN | +------------------------------------------------------------------+ | Bob Bethman \\\|/// " The absence of a danger | | \\ ~ ~ // signal does *NOT* mean | | [email protected] (/ @ @ /) that everything is OK " | +-------------------------oOOo-(_)-oOOo----------------------------+ ______________________________________________________________ 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
