>In <200207041336.g64Da0KF001984@contesting.com>, on 07/04/2002
> at 06:38 AM, Richard <2@mail.vcnet.com> said:
>
>
>
>>>the filiament voltage ........ for the 4-250A tubes can you go over a
>>>bit, say to 6 volts?
>
>>The emissive life of a thoriated tungsten cathode/filament varies as
>>[e1/e2]^23.4. Or, in other words, each 3% increase in fil. V over what
>>is needed to produce normal emission, reduces emissive life by half. A
>>healthy 4-250A produces normal emission at c. 4.8V. If the filament is
>>operated at 6.0V, life will be reduced to [4.8/6.0]=0.8^23.4=0.0054, or
>>0.54% of the normal emissive life. (''Care and Feeding of Power Grid
>>Tubes'', Eimac Co.)
>
>>>will this adversly affect the tube what i really need to know will it
>>>kill it right away.
>
>>No. The tube should last c. 80-hours instead of the normal 15k-hours.
>
>Not good at all!
>
>How hard is it to buck the input voltage to your filament transformer?
Piece o' cake. One can buck it in the primary or add R is series with
the bifilar fil choke to bring it down to c. 4.8v. I use small gauge TFE
wire for the latter purpose. At 15Arms #22 TFE runs warm to the touch.
#18 TFE will carry 30Arms. However, some breathing room around such
wires is obviously needed -- i.e., such wires should not be neatly
bundled.
>Drop it down by 12vac and you should be in the 5.0v range.
yes.
>You do this by
>placing a 12v filament winding to act against the mains supply voltage.
>Add a small, heavy-duty resistor in series with the primary to make
>smaller adjustments if necessary. Also, you can get relatively small,
>air-cooled buck/boost transformers to correct your mains supply to the
>hamshack. These generally offer a 6v or 10v correction; you could put one
>on each leg.
However, this will also drop the HV, which is not wonderful.
>
>>>...
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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