5v rectifier on a 6v tap

[TIMBO]

Hi guys, What would be the best way to achieve 5v supply for 5U4GB off a 6v/3.6A tap.
Series resistor or voltage divider.

My math is not too great with this stuff.Thanks

[PRR]

Voltage divider muse waste-off MUCH more current than the load needs.

For a 10 Watt load, that's intolerable.

Anyway a series resistor "forms" a voltage divider with the filament, but 5/6 efficient.

What is this, a 3A heater? 0.43 Ohms 3.9 Watts (use 10W part).

Note that you can NOT put other 6V tubes on this winding. The 5U4 heater is the cathode, so it will be sitting up at +400V DC, which will try to blow the guts out of 6V tubes with cathodes near ground.

[TIMBO]

Thanks PRR. The winding is separate and will only have the rectifier on it.

Can you supply a simple calculation for your findings, so I can see how it works.
Thanks again.

[sluckey]

The 5U4 wants 5V at 3A. If you power with 6V you must put a resistor in series to drop 1V, leaving 5V for the tube. The same 3A must flow through that resistor. Therefore, the resistor must equal 1V/3A or 1/3Ω. It will dissipate 3 watts. Double or triple the wattage for safety.

So, get a 1/3Ω resistor rated for 10 watts.

If you will really be powering with a 6.3V source then adjust the above numbers accordingly. The resistor needs to drop 1.3V at 3A. Therefore, the resistor would be 1.3v/3A or .43Ω and rated for 10 watts.

[DummyLoad]

Voltage divider muse waste-off MUCH more current than the load needs.

For a 10 Watt load, that's intolerable.

Anyway a series resistor "forms" a voltage divider with the filament, but 5/6 efficient.

What is this, a 3A heater? 0.43 Ohms 3.9 Watts (use 10W part).

Note that you can NOT put other 6V tubes on this winding. The 5U4 heater is the cathode, so it will be sitting up at +400V DC, which will try to blow the guts out of 6V tubes with cathodes near ground.

or 2 x .22R 5watt? see attached...


--pete

[TIMBO]

Thanks

[MakerDP]

Have you considered just using an EZ81 which runs off 6.3V? It is a noval socket though if that matters.

[jase128]

would 1.3V too high make a lot of difference??? on the Rectifier?

thanks


Jason

[kagliostro]

I'm curious ....

What about to use 4 x 10A diodes connected this way ?



EDIT: My Bad, a similar solution is on Merlin's site



http://www.valvewizard.co.uk/heater.html

..... Also, large bridge rectifier packages often have a hole in the middle so they can be conveniently bolted to the chassis.

Franco

[DummyLoad]

I'm curious ....

What about to use 4 x 10A diodes connected this way ?



EDIT: My Bad, a similar solution is on Merlin's site



http://www.valvewizard.co.uk/heater.html

..... Also, large bridge rectifier packages often have a hole in the middle so they can be conveniently bolted to the chassis.

Franco

why bother with an active part - resistors work just fine - cost less.


--pete

[PRR]

> would 1.3V too high make a lot of difference???

From 5.0V to 6.3V, life would drop from maybe 10,000 hours to maybe 500 hours.

Similar to running standard 120V incandescent lamps on 150V. Burns way bright, dies young.

[DummyLoad]

> would 1.3V too high make a lot of difference???

From 5.0V to 6.3V, life would drop from maybe 10,000 hours to maybe 500 hours.

Similar to running standard 120V incandescent lamps on 150V. Burns way bright, dies young.

https://www.youtube.com/watch?v=wRxHYHPzs7s


--pete   

[jase128]

> would 1.3V too high make a lot of difference???

From 5.0V to 6.3V, life would drop from maybe 10,000 hours to maybe 500 hours.

Similar to running standard 120V incandescent lamps on 150V. Burns way bright, dies young.

wow, I didnt realise such a small amount would make such a difference. It goes to show tolerances in components can make a big difference too !!!

thanks for the reply !

Jason

[TIMBO]

Hi guys, used DL's idea and it worked a treat.
With tube in measured 4.8v across the pins.