"Ian Bell" wrote in message
...
Just got an email from Maplin to say they are out of stock of their one
and
only type of mains transformer for tube supplies (250-0-259 @150mA and
6.3VAC secondaries).

Where else can I get something similar in the UK?

Hammond have their European HQ in the UK.
Danbury is a cheaper UK maker.
Sowter are top of the league - highly recommended.

Iain

Sounds like this is for a preamp, and in this case Phil is right on
the button. A couple of toroids back to back are perfect. If you use
230 to 12v and 12v to 230 you can not only take 12v AC for the heaters
but also rectify it to -15vDC for a constant current sink if you're
using a differential pair. But allow for enough current capacity and
seperate the toroids to allow for some cooling - be careful to check
the result for overheating.

Andy Evans wrote:
Sounds like this is for a preamp, and in this case Phil is right on
the button. A couple of toroids back to back are perfect. If you use
230 to 12v and 12v to 230 you can not only take 12v AC for the heaters
but also rectify it to -15vDC for a constant current sink if you're
using a differential pair. But allow for enough current capacity and
seperate the toroids to allow for some cooling - be careful to check
the result for overheating.



Yep, I have done that myself, but don't expect to get exactly 230v out
again, it will have two sets of copper losses.

Also, helpful though the idea is, I think the Maplin/Danbury TX's will
be cheaper than two toroids.

--
Nick

On Tue, 19 Jun 2007 12:20:33 +0100, Nick Gorham
wrote:

Andy Evans wrote:
Sounds like this is for a preamp, and in this case Phil is right on
the button. A couple of toroids back to back are perfect. If you use
230 to 12v and 12v to 230 you can not only take 12v AC for the heaters
but also rectify it to -15vDC for a constant current sink if you're
using a differential pair. But allow for enough current capacity and
seperate the toroids to allow for some cooling - be careful to check
the result for overheating.



Yep, I have done that myself, but don't expect to get exactly 230v out
again, it will have two sets of copper losses.

Also, helpful though the idea is, I think the Maplin/Danbury TX's will
be cheaper than two toroids.

I don't think exact voltages are going to be any kind of an issue for
this project. He is setting currents to measure noise figure - if the
volts are a bit wrong he may lose some headroom, but I think they will
be "adequate" whatever he does.

d

--
Pearce Consulting
http://www.pearce.uk.com

Andy Evans wrote:

Sounds like this is for a preamp, and in this case Phil is right on
the button. A couple of toroids back to back are perfect. If you use
230 to 12v and 12v to 230 you can not only take 12v AC for the heaters
but also rectify it to -15vDC for a constant current sink if you're
using a differential pair. But allow for enough current capacity and
seperate the toroids to allow for some cooling - be careful to check
the result for overheating.

I found this on Farnell. It's a 1:1 capable toroid

http://uk.farnell.com/jsp/Electrical...sp?sku=3919997

Forget it, it's no longer stocked but it ought to be possible to get 1:1 types.

Graham

Eeyore wrote:

Andy Evans wrote:


Sounds like this is for a preamp, and in this case Phil is right on
the button. A couple of toroids back to back are perfect. If you use
230 to 12v and 12v to 230 you can not only take 12v AC for the heaters
but also rectify it to -15vDC for a constant current sink if you're
using a differential pair. But allow for enough current capacity and
seperate the toroids to allow for some cooling - be careful to check
the result for overheating.


I found this on Farnell. It's a 1:1 capable toroid

http://uk.farnell.com/jsp/Electrical...sp?sku=3919997

Forget it, it's no longer stocked but it ought to be possible to get 1:1 types.

Graham


The only UK source for low vol 1:1 I have found is

http://www.antrimtransformers.com/

But in this case, the 1:1 doesn't also supply the heater voltage which
two back to back 230v:6v TX's would do.

--
Nick

On Tue, 19 Jun 2007 13:37:37 +0100, Nick Gorham
wrote:

Eeyore wrote:

Andy Evans wrote:


Sounds like this is for a preamp, and in this case Phil is right on
the button. A couple of toroids back to back are perfect. If you use
230 to 12v and 12v to 230 you can not only take 12v AC for the heaters
but also rectify it to -15vDC for a constant current sink if you're
using a differential pair. But allow for enough current capacity and
seperate the toroids to allow for some cooling - be careful to check
the result for overheating.


I found this on Farnell. It's a 1:1 capable toroid

http://uk.farnell.com/jsp/Electrical...sp?sku=3919997

Forget it, it's no longer stocked but it ought to be possible to get 1:1 types.

Graham


The only UK source for low vol 1:1 I have found is

http://www.antrimtransformers.com/

But in this case, the 1:1 doesn't also supply the heater voltage which
two back to back 230v:6v TX's would do.

I always found that for making low signal measurements on tubes it was
a good idea to supply the heater from a battery. Did away with all
sorts of mains hum nasties.

No good for a final design, of course - but that's another question.

d

--
Pearce Consulting
http://www.pearce.uk.com

On Tue, 19 Jun 2007 13:31:00 GMT, (Don Pearce)
wrote:

I always found that for making low signal measurements on tubes it was
a good idea to supply the heater from a battery. Did away with all
sorts of mains hum nasties.

No good for a final design, of course - but that's another question.

Agreed. A lead-acid accumulator is much better. ;-)

This brings back fond memories of my Beethoven Portable radio. This
had valves to die for and was powered from batteries - one for the HT
and a 'grid bias' battery which supplied around five different
voltages.

The output valve had a terminal on the top (from memory, the anode) in
addition to the terminals at the base. It was around 15cm tall.

--
Chris Isbell
Southampton, UK

"Chris Isbell" wrote in message
...
On Tue, 19 Jun 2007 13:31:00 GMT, (Don Pearce)
wrote:

I always found that for making low signal measurements on tubes it was
a good idea to supply the heater from a battery. Did away with all
sorts of mains hum nasties.

No good for a final design, of course - but that's another question.

Agreed. A lead-acid accumulator is much better. ;-)

This brings back fond memories of my Beethoven Portable radio. This
had valves to die for and was powered from batteries - one for the HT
and a 'grid bias' battery which supplied around five different
voltages.

The output valve had a terminal on the top (from memory, the anode) in
addition to the terminals at the base. It was around 15cm tall.



Last time I saw the Leicester Invester he had a big pile of bright
yellow industrial batteries that he intended to use to run a valve
amp..???

Chris Isbell wrote:
On Tue, 19 Jun 2007 13:31:00 GMT, (Don Pearce)
wrote:


I always found that for making low signal measurements on tubes it was
a good idea to supply the heater from a battery. Did away with all
sorts of mains hum nasties.

No good for a final design, of course - but that's another question.


Agreed. A lead-acid accumulator is much better. ;-)

This brings back fond memories of my Beethoven Portable radio. This
had valves to die for and was powered from batteries - one for the HT
and a 'grid bias' battery which supplied around five different
voltages.

The output valve had a terminal on the top (from memory, the anode) in
addition to the terminals at the base. It was around 15cm tall.


Thats annoying, I am now trying to find what the battery output valve
was with a top cap.

I am thinking of the likes of PT15 or 807, but neither of those are
"battery" valves.

--
Nick