Mains instead of battery?

[12jslater]

My radio needs a 120v battery. Could you run a 240v to 9v DC adapter into a 9v to 120v transformer instead of using a 120v battery in a radio?

Thanks, Jake

[Oldelectronics]

If I remember correctly? you cant transform DC. So you couldn't transform 9v DC even from a 9v battery to 120v DC. There are some very clever people on here who will able to explain why it wont work.

[Refugee]

Just use a stack of 9 volt batteries to make the voltage up.
DC to DC converters make too much interference on radios and are not worth it.
I made a 7.2 volt to 500 volt converter for a Megger than originally had an external power supply and it works very well.
120 volt transformers are easy to get and a simple resistor will get the voltage down to what you want after the rectifier.
You will also need a heater power supply too and that will need a very good and reliable regulator or the valve heaters will die.

[Skywave]

What you're asking won't work for one simple reason. The adapter produces 9 v. d.c. That 'd.c' abbreviation stands for 'direct current', i.e. the current only flows one way (convention states + to -). The transformer that converts 9v. to 120 v. requires that that input voltage of 9v. to be 9v. a.c. - alternating current. Alternating current changes its direction, + to -, very fast. A complete 'journey' from + to - and back to + again is called one cycle. The number of cycles per second is known as its frequency. That is measured in Hertz, abbreviated to Hz. (Used to be c/s: cycles per second). In the U.K., our a.c. mains supplies are 50 Hz - i.e. 50 cycles per second.

You seem to be unaware of how a transformer works, so here's a basic description of how one works.
Transformers only work with a.c. The changing direction of the current in its primary winding sets up a changing magnetic field in the core of the transformer and the changing magnetic flux in that core cuts the secondary windings of that transformer and an a.c. voltage appears across that secondary winding. The essential idea is that of a changing magnetic field. You won't get that with d.c.: you'll get a static magnetic field instead. The ratio of input volts to output volts = the ratio of number of turns on the primary to the number of turns on the secondary. Since the number of turns can be chosen by the transformer manufacturer, the ratio of input to output voltage can be easily chosen.
Actually, there is a good deal more to transformer design than all that, but what I've written are the basics.

In days of old, what you are looking for used to called a battery eliminator. You fed mains a.c. in and it produced d.c. out, typically in the range 90 to 120 v.d.c. Needless to say, a transformer and a rectifier (a.c. in; d.c. out) were two essential parts of such a unit.

HTH,

Al.

[Skywave]

Originally Posted by Refugee

Just use a stack of 9 volt batteries to make the voltage up.

Hmm: O.K., let's do the arithmetic. 120 v. ÷ 9 = 13.3. In actual point of fact, "9v." batteries start at about 9.2 v. So 9.2 times 13 = 119.6. That's close enough to 120. Mind you, thirteen 9v. batteries will be a tad expensive.

Al.

[Refugee]

9V batteries can often be had in 2 packs for a quid in pound shops so 12 is best.
13 can be an unlucky number to some people anyway.

[Oldelectronics]

If you put something like this into E Bay EverReady battery B141 Complete replacement kit. You may find what you want.Usually 90v plus valve heaters but would do one offs for other battery's?And they use cheap PP3 battery's

[marconi_pete]

The general consensus is to build up the required voltage with 9 volt batteries. There is another way you could get 120 volts DC from a single 9v DC battery and that is to modify an old nixie clock psu. It usually has an input voltage of 9 or 12 volts DC and you simply change a resistor to get the required DC output voltage. I've used these on many valved battery sets and they work rather well.

Thanks,
Peter

[Phil G4SPZ]

Jake, if you would like to visit Griptons sometime I can show you a selection of replica HT and LT batteries plus some battery eliminators.

I agree with everyone else that a stack of pound-shop PP3s is by far the cheapest, easiest and safest option for the HT supply. What were you proposing to use for the LT? If the radio requires 2 volts you'll need to acquire a Cyclon cell and a means of recharging it. You could also use two NiMH cells with a diode in series, but do check that the voltage on load doesn't exceed 2 volts or you may damage some rare valves.

[marconi_pete]

Forgot to mention. The nixie power supply also has a separate tap for 5VDC in addition to the high voltage HT. You can use a resistor to drop it to 2v so the same psu can supply both the HT and LT

[threeseven]

It can be done with a DC to DC convertor. This is a device that internally converts a DC source at low voltage to AC via a switch mode circuit, then rectifies and regulates that to DC at a high voltage. Some research on ebay will find circuit modules of this type from Chinese sellers at very low prices. There are various different types for different voltages, some fixed, some variable.
For example, I bought one to convert 12 VDC to 24 VDC to operate a soldering iron of that voltage from a car battery, for convenience when working on cars. The one I chose is surprisingly good quality for the very low price paid, and works perfectly.

This is the sort of thing, with it's adjustment range it will do 90 and 120 vdc.

http://www.ebay.co.uk/itm/High-Volta...QAAOSwXeJYCGwF