Could this be a form of cathode interface problem? Cathode interface is a problem sometimes seen when old tubes are used in scope vertical amplifiers with fast risetimes. Something happens to the tubes that causes the actual rise time to deteriorate as the tubes age. The "something" that happens is called cathode interface. I have observed this effect personally on old Tek scopes so I know it is real and apparently widely recognized. But I don't know if anyone has done any work to see if cathode interface has an impact in other tube applications like audio amplifiers.
Anyway, I just thought I'd throw that idea into the discussion. I am no expert and my ears prefer solid state audio. 73, Don Merz, N3RHT -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Todd Bigelow - PS Sent: Thursday, October 02, 2003 9:25 AM To: amradio@mailman.qth.net Subject: Re: [AMRadio] Testing tubes Larry Szendrei wrote: >Bill sez: > > >>All tubes tend to loose high frequency tone with age. Kind of a softening of >>the high frq. response. But will still test good in a >>standard tester that uses line frq.as a signal source. >>The exception is the Weston testers which use an internal >>osc. at 5 khz which gives a more realistic test of the sound of >>the tube. >> >> > >and Larry respecfully sez: >I have a heard time swallowing this one. If tubes lose gain at the >higher audio feqs. with age, it then follows they'll stop amplifying RF >a heck of a lot sooner. I've never observed either phenomenon. > >But I'd be happy to be proven wrong with some hard data. :>) > >-Larry/NE1S > I agree with Larry if for no other reason than this: considering the bulk of tubes out there now (NOS and used) are of 20+ year manufacture dates, how can the great response heard in so many fine receivers be explained? Why also would the audiophools be paying so much for old tubes, Amperex, Phillips, or otherwise, if the high end response was somehow 'softened'? What is the mechanism for somehow attenuating amplification in the same tube that would somehow pass all other frequencies just fine, and why? Tuned Mechanical Plate filtering? If a tube loses anything like this over the years, I'd suspect it would be across the board myself. I'll even back that up with an equal amount of proof and expertise as that given to support the 'softened highs' theory. OTOH, it *is* true that humans tend to lose their high frequency hearing first compared to the rest of their aural range. Maybe the golden ear crowd is looking to blame those poor old tubes for the inevitable evolution of golden ears to tin? Hey Larry - you planning to be at HossTraders? de Todd/'Boomer' KA1KAQ _______________________________________________ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio DISCLAIMER: The information contained in this e-mail may be confidential and is intended solely for the use of the named addressee. Access, copying or re-use of the e-mail or any information contained therein by any other person is not authorized. If you are not the intended recipient please notify us immediately by returning the e-mail to the originator.(A)
