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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 21st October 2013, 06:08 AM   #1
rmyauck is offline rmyauck  Canada
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Default Pete Millets Big Red Board

Magnetic Ballast (Sylvania) MB2 x 40/120 RS
I bought 2 fluorescent light ballasts for $13-14 ea a few yrs ago, I'm wondering if they could be used as PS for the B+ of a tube amp. They are for a pair of 40W bulbs. Lots of wires though!


120V @ 60 Hz

0.74 Amps


Lot's of mA capability by the looks of it if they would work. Maybe could be used in a voltage doubler PS if needed.

I was thinking of using them for Pete Millet's Big Red Board!

I just got this question above closed on the Tube Form as a moderator thought I need an isolation transformer. I was just asking a question! Do I?

They're just basically transformers right even though it says magnetic ballast? I read you can get 280-0-280 with 740 mA right? with 120V in

Last edited by rmyauck; 21st October 2013 at 06:14 AM.
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Old 21st October 2013, 02:23 PM   #2
Tubelab_com is offline Tubelab_com  United States
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A flourescent tube ballast provides 3 functions. It must provide a high voltage to strike the arc through the mercury vapor. This is the 280 volts Open Circuit Voltage that you see. Second it must limit the current theough the mercury plasma. This is the .74 amps. The OCV and the load current are not available at the same time. The voltage under load will be much less, somewhere around 30 volts depending on the temperature in the tube. Third the balast must light the filaments inside the tube.

None of these functions are compatible with a tube amp, and I doubt the ballast is isolated so your source, CD player, iPOD or turntable may be LIVE with LINE VOLTAGE. There is no way that you can use this for a power transformer.

I have seen people use these things for chokes in the B+ supply. The current limiting function is achieved by an inductance in series with the line, so it could be used as a choke, but I don't care to speculate about the quality of them. I have never tried it.
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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Old 21st October 2013, 02:40 PM   #3
rmyauck is offline rmyauck  Canada
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Thanks George!

Just thought from googling that it has a transformer & I thought transformers were always isolated and it definitely contains one by the wt. So you could get 250V?

Might have to try it as a choke!
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