01-06-2013, 05:11 PM
Some time ago I saw a design for a battery eliminator by Tony Thompson, 'Aerodyne'. I didn't keep a copy of this but did remember that the transformer he used came from Bardwell's, which is an old-fashioned electronics shop near me. This is a dual secondary giving 8-0-8 + 43-0-43.
An LM317 sorted out the LT side fine but the HT needed more thought. Off-load it was producing 135V which only dropped to 110V when connected to my Bush BP90. It seemed like a lot to expect another LM317 to deal with and I was loath to use two. I therefore fitted a TL783.
Further calculations and tests revelled that the setting resistors for an LM317 would pull the voltage down enough for the chip itself to cope with but having already ordered the TL873 I stuck with that.
Bardwell's (http://www.bardwells.co.uk/) do mail-order but their web-site is poor and it's better to ring them as they have far more stuff than is listed on it.
If one of these transformers isn't available I expect that the 110V tapping of the transformer from a shaver socket would be OK. These are rated at 20VA so should be more than enough.
I couldn't find a high-power 5.6kΩ resistor so used a network of 10kΩ and 1kΩ ones.
I did the electronic side a few weeks ago but couldn't finish it as I run out of mains switches and was waiting for more to wend their way from the Mysterious East. They arrived earlier this week but it was then too wet to go out to cut the wood.
I've made something of a mess of the ventilation holes but I realised I was pushing my centre-punching skills and at least it does the job.
- Joe
An LM317 sorted out the LT side fine but the HT needed more thought. Off-load it was producing 135V which only dropped to 110V when connected to my Bush BP90. It seemed like a lot to expect another LM317 to deal with and I was loath to use two. I therefore fitted a TL783.
Further calculations and tests revelled that the setting resistors for an LM317 would pull the voltage down enough for the chip itself to cope with but having already ordered the TL873 I stuck with that.
Bardwell's (http://www.bardwells.co.uk/) do mail-order but their web-site is poor and it's better to ring them as they have far more stuff than is listed on it.
If one of these transformers isn't available I expect that the 110V tapping of the transformer from a shaver socket would be OK. These are rated at 20VA so should be more than enough.
I couldn't find a high-power 5.6kΩ resistor so used a network of 10kΩ and 1kΩ ones.
I did the electronic side a few weeks ago but couldn't finish it as I run out of mains switches and was waiting for more to wend their way from the Mysterious East. They arrived earlier this week but it was then too wet to go out to cut the wood.
I've made something of a mess of the ventilation holes but I realised I was pushing my centre-punching skills and at least it does the job.
- Joe