[R-390] RE: More BallasTube Noise

[Cecil Acuff]

INCOMING>>>>

----- Original Message ----- 
From: "Drew Papanek" <drewmaster813 at hotmail.com>
To: <r-390 at mailman.qth.net>
Sent: Thursday, February 10, 2005 2:44 PM
Subject: [R-390] RE: More BallasTube Noise


>
>
>
> Brian wrote:
>
>>hi, just as a matter of interest about 7 weeks ago i purchased on uk ebay
>>2 3tf4 ballast tubes both are nos for $18 the pair. i put one in my 390a
>>whicth i use most days and so far it is fine, sure it glows alittle more
>>red but is this another and cheaper way to keep the 390a running.
>
> The 3TF4 used in that way will operate above its upper voltage limit with 
> attendant shortened life.
> One could insert resistance in series to reduce dissipation;  the value 
> would range from 15 ohms to 28 ohms.  Dissipation would range from about a 
> watt and a half to two and half watts.
>
> Alternatively, a diode could be inserted in series with the 3TF4.  The 
> 25.2v secondary when half wave rectified  would have an RMS value of 
> 17.8v, 12.6V would be dropped by the 6BA6 heaters and the 3TF4 would see 
> 5.2v.
>
> The BallasTube can be dispensed with entirely.  Substitution schemes 
> abound. Goto r-390a.net    click on References, Pearls of Wisdom, Ballast 
> Tube.  There you will find out more than you ever wanted to know.
>
> Drew
>
>
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