Cheap transformer for valve experiment

[snip]

Hi, I want to experiment with building a few different valve buffer stages.

I am looking for a transformer that gives 6.3V and 110V out, to construct a lampizator "totem pole" type circuit, also on the hunt for a ~300V

Anyone come across any for cheap recently, or maybe someone has one laying about that they are not using?

I have been looking around the usual websites but cannot seem to find any suitable ones, except for expensive ones on eBay.


//Jan

[smurfbrain]

have you had a look at
http://www.airlinktransformers.com/
or
http://www.radiotronics.co.uk/products.php?cat_id=1303
or
http://www.canterburywindings.co.uk/

First two are the cheapest. Airlink(theres section with custom trafos and prices) and CW will do a custom job.

[snip]

have you had a look at
http://www.airlinktransformers.com/
or
http://www.radiotronics.co.uk/products.php?cat_id=1303
or
http://www.canterburywindings.co.uk/

First two are the cheapest. Airlink(theres section with custom trafos and prices) and CW will do a custom job.

Thanks, I am sure those thinks will come in handy for future projects,

however this particular project is under very thin shoestring constraints, I have to find the cheapest way possible to get ~180V DC and 6.3 or 12.6 either AC or DC.

Last night I was looking at this little circuit I pulled out of a cheap maplin solder station that had given up the ghost, it literally regulates the mains voltage using a BT136, I thought about connecting a rectifier to that and using that as my HT:stalks:. I came to my senses and kept thinking, then it struck me:bulb: those converter thingy's for using amurikan thingys, they must contain a mains transformer that gives out 110V right?, so technically nothing wrong with getting one of thoe for like a fiver off eBay and using that for the HT supply?, then a low voltage lighting transformer for the heater supply and I'd be in business for peanuts.

But just checking, the idea of using the mains voltage regulator, effectively a dimmer on a rectifier, that is really as wrong as it seems to me right? Certainly would be illegal in Denmark.

//Jan

[Tom472]

I would lean towards the USA/Europe transformer given the choice.

You'd need a lot of regulation to get any kind of steady DC out of a triac dimmer control, and it may not work at all if you can't pull enough current through the triac to keep it conducting.

The USA/Europe adapters will most likely be modern switched power supplies - not ideal for audio but should work.

The old trick for this sort of thing was to find two old 6 or 12v transformers from an old piece of equipment and run them together so you have 230v - 6v - 230v. This would give you 230v rather than 110v, but you should be able to get a buffer circuit to work with any old voltage really. Or you could find 230v - 6v and 230v - 12v transformers to give you 230v - 6v - 110v.

Hope that helps.
Regards
Tom

[snip]

I would lean towards the USA/Europe transformer given the choice.

You'd need a lot of regulation to get any kind of steady DC out of a triac dimmer control, and it may not work at all if you can't pull enough current through the triac to keep it conducting.

The USA/Europe adapters will most likely be modern switched power supplies - not ideal for audio but should work.

The old trick for this sort of thing was to find two old 6 or 12v transformers from an old piece of equipment and run them together so you have 230v - 6v - 230v. This would give you 230v rather than 110v, but you should be able to get a buffer circuit to work with any old voltage really. Or you could find 230v - 6v and 230v - 12v transformers to give you 230v - 6v - 110v.

Hope that helps.
Regards
Tom

Ah yeah, that's not a bad idea. I have to keep the final DC voltage under 300V though, that is the maximum of the valve I will be using

I had been thinking that the eu/usa converters these days were probably nasty SMPS devices and not straight transformers.

The key concept here is that it has to be well cheap, spending £40 on a transformer is just not on. If it turns out to be really super lovely then I may eventually build it with a nice transformer and nicer capacitors, etc.

I have this plan in the back of my head of having the boards from my 7510 in a nice chassis, valve output stage on the DAC, with a little relay that switches the input over to a valve based RIAA stage when the dac is turned off and a stepped attenuator going either straight to output RCA's or through another buffer stage. Thus having a complete pre amplifier with a RIAA stage and four digital inputs.

//J

[snip]

Oooh, brainwave...

I have some old encapsulated PCB transformers, .5 VA or something, that are 6V output somewhere, so I could just get a 12V transformer for low voltage lighting, run that into the secondary windings of the little pcb transformer, and also into a rectifier, and then a rectifier on the other end of the pcb transformer, thus landing me with ~170V and ~14V DC, just what I need to do the job.. Tidy!

//J

[snip]

Aha, I found a 12V PCB transformer, 6VA with two 120V primaries.
So here is how I propose to hook it up
http://www.snip.dk/temp/HTsupply.PNG

The 12V AC is going to come from one of those slimline low voltage lighting transformers that I picked up for £3, including delivery! :) It should be good for 60W i.e plenty, I reckon if I have that externally I should be able to fit the lampizator into a very small potting box.

//J

[Tom472]

Thats the badger.

Make sure you monitor the heat from the LM317 - should be ok, but they can get pretty toasty when they have to drop a lot of volts - may need a dinky little heatsink.

Regards
Tom

EDIT: hang on a minute, if the second transformer is 240v primary and 6v secondary, and you feed 12v ac into its secondary, you'll have 480v at the end won't you?

[snip]

Thats the badger.

Make sure you monitor the heat from the LM317 - should be ok, but they can get pretty toasty when they have to drop a lot of volts - may need a dinky little heatsink.

Regards
Tom

EDIT: hang on a minute, if the second transformer is 240v primary and 6v secondary, and you feed 12v ac into its secondary, you'll have 480v at the end won't you?

Yes, sorry it's a split bobbin either end, I will connect both the 12V windings in parallel to the incoming 12V and use one of the 120V windings on the other side it was just that I did'nt have a good symbol for that.

//Jan

[snip]

Aha, I found a 12V PCB transformer, 6VA with two 120V primaries.
So here is how I propose to hook it up
http://www.snip.dk/temp/HTsupply.PNG

The 12V AC is going to come from one of those slimline low voltage lighting transformers that I picked up for £3, including delivery! :) It should be good for 60W i.e plenty, I reckon if I have that externally I should be able to fit the lampizator into a very small potting box.

//J


mm actually that second electrolytic on the heater supply is obviously not meant to be 10.000uF, 10uF should do it, Such a large one would blow the lm317T during charging I think.

//J