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


ronnie.hull at glowbugs.com ronnie.hull at glowbugs.com
Wed Aug 26 08:13:58 EDT 2009


This has been an interesting thread to be sure. Gentleman I have 3  
450TL's that I got from Geoff a few years ago and I have two used  
known good 250TH's that I have no use for.

I would be willing to trade all 5 for a usable 3-1000Z. The 450TL's  
are nib box the boxe's are falling to peices.

I also have a filament tranny that would work for those 450TL's that I  
would be willing to throw in.

Ronnie - W5SUM


Quoting crawfish at surfmore.net:

> 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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