Using Telefunken "Tank" transfomers for a single ended el84 amp? - Page 2 - diyAudio
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Old 8th March 2004, 11:55 PM   #11
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Hi,

Quote from Glassware:

Quote:
The Voltage Doubler power supply configuration allows the creation of a power supply whose output voltage far exceeds the peak transformer secondary voltage. Two diodes, two capacitor--that's all there is to it. Only one half of the voltage cycle is used in each leg of this circuit, that is, one diode conducts, then the other--each builds up a voltage in its associated capacitor, which are in turn stacked one above the other, thus, doubling the voltage.
So what you need is 2 * 1N4007s , a cap of say 470F/250VDC that goes inbetween the tiepoint of the diodes and finally another cap of say 47F/400VDC to build your basic supply.

It will yield a voltage much higher than you require for the EL84s and the input tubes but at least you can now smooth further by either RC filtering or better still choke filters.

Keep in mind that the total current available is only half of what the xformer could have delivered without the voltage doubler.

Cheers,
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Old 9th March 2004, 12:12 AM   #12
ark is offline ark  United States
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Thanks. That's very interesting.
I have a filter choke someplace:
(CHICAGO TF1A04YY Filter Choke. 5HY 400ma. 60 ohm DCR)
Too big?

That will knock the voltage down a bit right?

I'm wondering now: where do I rectify to DC then?
Before or after the Diode doubler?

I still really want to use a tube rectifier if only for aesthetic reasons.
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Old 9th March 2004, 12:31 AM   #13
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Hi,

Quote:
That will knock the voltage down a bit right?
The 5H will be fine, bigger is even better but since this is what you have...

The 60 Ohm DCR won't bring the voltage down enough, you'll only need about 250VDC and you're looking at about 400VDC coming from the doubler.

Actually if you'd had about 10VAC more from the xformer a bridge rectifier would have worked fine....
There are tricks to add another xformer to the secondary but I'm no big fan of those stunts.

Quote:
I'm wondering now: where do I rectify to DC then?
Reread the quote I pasted in the previous post; it's done...finito, simple as that.

Quote:
I still really want to use a tube rectifier if only for aesthetic reasons.
Stick a candle on top of it...??
Seriously, do whatever you fancy but you can't have your cake and eat it too...so it's either the diodes as doubler or a totally different project altogether.
A preamp iso an amp for example, even so B+ will inevitably on the low side of good.

Cheers,
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Old 9th March 2004, 12:32 AM   #14
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For EL84s (better yet SV83s), i'd just bite the bullet and put a diode bridge on the 177V... you should get somewhere around 240 V -- maybe a bit low (you won't get quite as much power), but still fine. Use the choke in a CLC to get as little voltage drop as possible... the 6DJ8 will be more than happy with what you get.

dave
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