[R-390] Ballast Tubes - Resistor

[Dave Maples]

All: Just a minute.  Two 6BA6s in series will draw 12.6 V at 300 ma, not 600
ma.  If the supply voltage is 25.2 volts, then:

Resistor value = (voltage to drop) / current through resistor

Resistor value = 12.6 / 0.3 = 42 ohms

Best fit: 47 ohms // 390 ohms (comes out to 41.945 ohms)

Power through resistors = E**2 / R

(12.6 * 12.6) / 47 = 3.37 watts

(12.6 * 12.6) / 390 = 0.407 watts


A 47-ohm, 5 watt resistor in parallel with a 390-ohm, 0.5 watt resistor
should do the trick.

Dave WB4FUR

-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net]On Behalf Of David C. Hallam
Sent: Saturday, July 03, 2004 1:30 PM
To: R-390 List
Subject: [R-390] Ballast Tubes - Resistor


According to my RCA Tube Manual a 6BA6 is rated 6.3 V at 300 mA, so 2 tubes
in series 12.6 V at 600 mA.  Supply voltage is 25.2 V so you want to drop
12.6 V with 600 mA of current

12.6/0.6 = 21 ohms

21x0.36 = 7.6 watts

A resistor ( 21 ohms at 10 watts would seem right

David C. Hallam
KC2JD


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