[Amps] toroid filament choke?

[R.Measures]

On Oct 27, 2004, at 7:24 AM, Tony King wrote:

> At 10:13 AM 10/27/2004, k7fm wrote:
>> Will said:
>>
>> "You have to keep in mind the current surge there until the heater 
>> warms up.
>> The colder the heater is, the more current it draws. I would use a 
>> conductor
>> with at least 750 cir mils per ampere. For 3 amperes, that equals out 
>> to be
>> about 16 AWG wire for the minimum"
>>
>> The filament choke should not take into account any surge current, 
>> and there
>> is an advantage in limiting the wire size to limit surge current.  By
>> limiting the wire size, the smaller wire will limit the surge current 
>> and
>> protect the tube.  Since the choke is presumably in the slipstream of 
>> air, a
>> significantly smaller size of wire can be used.  If there is no other 
>> means
>> to protect the filament surge current, then this is an opportunity to
>> protect the tube and wind a smaller choke.
>>
>> Since chokes always seem to be just large enough to not fit where you 
>> want
>> them to, take advantage of downsizing.
>
> Very interesting guys!  I was thinking that with a step start on the 
> filament, the surge would be of little consequence anyhow. Keeping the 
> choke smaller would certainly make it easier for constructing the 
> input and even more desirable for those folks that are thinking of a 
> retrofit to desk top amps.
>
> Based on Rich's earlier comments I would think you could easily go 
> smaller than #16 wire on the choke and reduce the physical size or at 
> least get enough inductance for 160 in the same package. What do you 
> think the target inductance should be for effective use on 160?
>
Tony --  The stock, 9uH, filament choke in a SB-220 works okay at 
1.8MHz provided that one adds -j100-ohms of XC (900pF) to C2 of the 
160m tuned input to cancel the +j100-ohms of XL from the 9uH.

> 73, Tony W4ZT
>
>
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org