• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Power supply transformer for pre-amp

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baudouin0

Member
Joined 2019
Could somebody recommend a transformer for a valve pre-amp with a 12ax7 and a 12at7 the first valve may need DC heater as I need some gain. So I need heater + HT with HT about 170-200V maybe about 3W HT. Problem is I need something off 230V UK mains. Hammond only do 115V mains.

20200619_180409.jpg



As I have just made this schoolboy error.


Something new I can order.



Cheers.
 
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Eli Duttman

Member
Joined 2004
The economics of being able to use that which is already on hand may make the Triad N-68X isolation trafo, with its "universal" primary configuration, a good choice. Step "230" VAC down to "115" VAC.

UK VAT and duties, along with regulations, may make this idea a non-starter. In the US, we deal with state and local sales taxes. Canadians get walloped with goods and services tax (GST) plus provincial sales tax (PST). No matter where you live, taxation is a PITA.
 
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Blaxshep

Member
Joined 2017
Eli Duttman said:
The economics of being able to use that which is already on hand may make the Triad N-68X isolation trafo, with its "universal" primary configuration, a good choice. Step "230" VAC down to "115" VAC.

UK VAT and duties, along with regulations, may make this idea a non-starter. In the US, we deal with state and local sales taxes. Canadians get walloped with goods and services tax (GST) plus provincial sales tax (PST). No matter where you live, taxation is a PITA.
Click to expand...

Ditto, I was going to suggest Triad. I use them alot.
 
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Eli Duttman

Member
Joined 2004
Perhaps a "wall wart" can be constructed containing the N-68X. It seems that UK wall outlets, like their US counterparts, are safety grounded. Acquire a UK computer power cord made with adequate gauge wire and cut it into 2 parts. That takes care of the wall connection and the IEC power inlet connector on your chassis.
 
petertub

petertub

Member
Joined 2015
tubular-well.se
Paid Member
PRR said:
In the US, the Dyna-clone transformer would probably work gret (depending how hot the 12AT7 works).
PA211 Power Transformer Dyna PAS for Dynaco Replacement MADE IN USA

I do not know if there is a source on your side of the postal/shipping jam-up.
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These transformers are very much limited in capacity. 15mA is the limit !


Yes, there is swedish compatibles with PS522, but they are still limited

to 30mA http://n.manet.nu/tubedoc/ENO19023.pdf


The toroids from tubetown.de is a much better alternative, they are also

offered in several sizes.
 
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baudouin0

Member
Joined 2019
Primary windings have a 200v HT 6.3V part so that will do me just fine. That decided on the HT voltage then of 280V! They are a little less common than I was expecting. Maybe valve pre-amps are not that common.



Thanks for all the help much appreciated.
 
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petertub

petertub

Member
Joined 2015
tubular-well.se
Paid Member
Zeta4 said:
Maybe PrimaryWindings.com in the UK might have something suitable. They have a range of transformers for valve pre and power amps. Ive used then for a valve headphone amp and found them good quality.
Click to expand...
Thanks for the tip of "primary windings", new to me.
Especially valuable in europe, and let's hope that we can buy from UK

as easy as we can buy within EU.
 
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