GB> Re: Tubes in Series was (Re: [Heathkit] Question on 12AU7) LONG

[N2EY at aol.com]

In a message dated 2/3/08 8:31:44 AM Eastern Standard Time, 
km1h at jeremy.mv.com writes:


> Also consider that those tubes (along with the 12AX7, 12AT7, etc) were used 
> 
> in mobile applications where heater voltages were far from steady and could 
> often exceed the 10% rule. Yet they seemed to fail at no higher a rate than 
> their AC line operated brethren.

It's hard to know how many hours those tubes really got, though.

Consider this: If a car is driven at an average speed of just 20 MPH, when 
the car reaches 200,000 miles it will only have 10,000 hours on it. And in the 
days of tube-type mobile gear, very few cars lasted 200,000 miles. 

But a radio which is on 24/7 will accumulate 10,000 hours in a little more 
than a year.

> 
> Octal based tubes such as the 6K8, 6SG7, 6H6 and similar were used in AC-DC 
> radios and they did not have controlled warmup time. Yet they worked just 
> fine and lasted a long time.
> 

Because their heaters were all very similar in wattage and thermal 
characteristics.

73 de Jim, N2EY




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