> FILAMENT OPERATION - The rated filament voltage for the
> 3-500Z is 5.0 volts.
> Filament voltage, as measured at the socket, should be
> maintained within the
> range of 4.75 to 5.25 volts to obtain maximum tube life.
> Ive always believed that when in doubt follow the
> recommendations. Unless you have a big budget that is.
Which agrees with what I wrote and what Carl even was kind
enough to repost:
>> The real truth is if the voltage on your 3-500Z is
>> between 5
>> or 5.25 volts, or even if it is a little high, it won't
>> a bit of difference in the life of the tube if you lower
>> to some magical number. You won't see 10,000 operating
>> in amateur service, and you almost certainly won't have a
>> tube that fails because of low emission unless you run
>> thing at 6 volts. If you keep the voltage somewhere near
>> volts it will be like 99% of all the other tubes that
>> and dies from something you really can't control.
>> The main reason you have taps on that transformer is to
>> the HV. The bandswitch and tuning cap, because of cost
>> necessity in the Ham market, don't have a lot of
>> The most damaging thing is to let the HV get too high, so
>> the taps allow you to keep the HV at a reasonable value
>> exceeding a safe margin.
>> The filament, if you watch the HV and follow guidelines,
>> will be right in the ballpark. This is why the manual
>> you to set the tap to the next HIGHER voltage UP from the
>> maximum voltage you expect to see.
Watch the HV or pick the right taps, and the filament will
take care of itself.
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