14v from 5v supply

[TIMBO]

Hi guys, Do voltage doublers work on low voltage.

I've got some 14gw8, so a heater supply of around 14v is needed.

Would a voltage doubler on a 5v tap do the job??

[pdf64]

You might get close enough, but as doublers are saggy under load, it may be a good idea to select low loss diodes, eg shottky type, and reservoirs with high capacitance (eg >1000uF) and low ESR.

[TIMBO]

Thanks, might do some experimenting.

[jjasilli]

Voltage doubling should yield 2X the AC peak voltage. 5VAC RMS = 7.07 peak X 2 = 14.04 VDC.  The tube specs say 13.3V @ 300mA.  The 5V supply is probably good for 2A??? Doubling will effectively reduce that to 1A.  A 300mA draw should be OK. 


Worst case: 13.3 VAC RMS = 18 VAC peak.  So you can double the 5 VAC supply twice > 28 VDC.  This may sag to a good voltage; or drop it or regulate it down.  Your 2A 5V supply is now down to a 500mA rating, but still good enough for the 300mA draw.  This is meant as positive illustration; please check your actual values.

[darryl]

A separate small heater transformer would be much simpler. The heater requirements of two 14GW8's could be supplied by a 15-volt transformer such as: https://www.jaycar.com.au/6-3-15v-15va-1a-multi-tapped-type-2155/p/MM2002

The total heater required is 600mA, so to drop the transformer's 15VAC tap to a nominal 14VAC would require a series resistance of 1/0.6 = 1.7 ohms  The resistor's heat dissipation would be approximately 2 watts, so a 1.8 ohm, 5 watt resistor would be suitable.

[PRR]

I agree with both the above. The doubler with large caps may get close enough to the 13.3V rating, but just-barely. A heater transformer with a dropper is sure to work but eats the price of a cheap lunch.

[DummyLoad]

my SIM shows 11.5V loaded - sim run with schottkey diodes and low ESR 1200uF/2200uF electrolytic caps.


try a 24V 10VA transformer - wire 14GW8 filaments in series - you should be able to source a 24V control transformer for just a few bucks.


--pete

[TIMBO]

Thanks guys, As it turns out finding a low HT (around 300v after rectifying @ 100mA) that has a 5v tap is kinda not available

So a extra transformer as Darryl has noted will do the job.
Thanks

[jjasilli]

No fairness.  I assumed you already had the tranny on hand. 

[TIMBO]

Sorry about that, JJ

 I"m sure your info WILL be used in the future.

[rake]

My first thought was "wouldn't a transformer be cheaper"????
then I had to laugh because I was considering something similar
on a project of my own! (more on that later)

I guess it's just the nature of guys (and gals) who build their own mousetraps
to over think from time to time!

(then followed up by a great big DUH!)

[pompeiisneaks]

another option would have been to use a voltage tripler (15-18VDC possibly?), and then put that into an appropriately setup voltage regulator like Dumble did in his amps.  I've used that one and have like 18V going into the regulator and it outputs a good 11.88V to the relays. 

~Phil