[AMRadio] Testing tubes

[Todd Bigelow - PS]

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