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Re: [Amps] AL-80B transformer tap

To: "jeremy-ca" <>,"James M. Daly" <>, <>
Subject: Re: [Amps] AL-80B transformer tap
From: "Tom W8JI" <>
Date: Mon, 23 Jul 2007 12:15:32 -0400
List-post: <>
Carl wrote:
> 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 
> manufacturers
> 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 
>> make
>> a bit of difference in the life of the tube if you lower 
>> it
>> to some magical number. You won't see 10,000 operating 
>> hours
>> in amateur service, and you almost certainly won't have a
>> tube that fails because of low emission unless you run 
>> the
>> thing at 6 volts. If you keep the voltage somewhere near 
>> 5
>> volts it will be like 99% of all the other tubes that 
>> fail
>> and dies from something you really can't control.
>> The main reason you have taps on that transformer is to 
>> set
>> the HV. The bandswitch and tuning cap, because of cost
>> necessity in the Ham market, don't have a lot of 
>> headroom.
>> 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 
>> not
>> 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 
>> tells
>> 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.

73 Tom 

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