stepdown transformer - Electronic Circuits Projects Diagrams Free

jjac7212 · 7th April 2008, 10:14 AM

Hey guys, im from australia and am trying to build an american guitar amp
anyway i have a problem with the transformer and just needed to know two things. one is that my local store sells a good transformer that gives pretty decent compatibility with the circuit in terms of voltage, it takes the 240 volt aus power. the two bottom taps are 15v and i need a 5v and a 6.3v for these, so how would i calculate the right resistors for these taps to connect to, to bring the voltage down to the right value?
secondly, would it be easy for a noob like myself to wire up a transformer myself? im trying to save a little money and get the voltages closer.

RODALCO · 7th April 2008, 10:45 AM

It looks that you have a valve amplifier with 6.3 volts ac for the heaters.

Normally they are fed from a dedicated 6.3 Volts ac winding of the TX.

You can use a 5 Volts regulator (7805 or 7805 + 2 diodes in series on the negative to get 6.2 volts, for the valves, or an LM 317 and set it for 5 volts or 6.3 volts but it would be very inefficient.
E.G. 1 Amp at 15 - 6.3 Volts 8.7 volts = 8.7 watts dissipated in heat.

It is better to have for the valves a dedicated 6.3 volts ac winding.

Also a transformer gives ac which you will need to rectify to dc via a bridge rectifier, and filter capacitor.

**Nigel Goodwin** · 7th April 2008, 11:33 AM

Quote:

Originally Posted by jjac7212

Hey guys, im from australia and am trying to build an american guitar amp
anyway i have a problem with the transformer and just needed to know two things. one is that my local store sells a good transformer that gives pretty decent compatibility with the circuit in terms of voltage, it takes the 240 volt aus power. the two bottom taps are 15v and i need a 5v and a 6.3v for these, so how would i calculate the right resistors for these taps to connect to, to bring the voltage down to the right value?
secondly, would it be easy for a noob like myself to wire up a transformer myself? im trying to save a little money and get the voltages closer.

It sounds like your transformer is totally unsuitable, any valve transformer is likely to include a 6.3A winding, so what is the transformer designed for?.

Assuming the rest of the transformer is OK?, then simply use a separate heater transformer for the 6.3V.

RODALCO · 7th April 2008, 11:45 AM

Where do you need 5 volts for in a valve amplifier ?

I was pondering about that one over the last hour.

Normally 6.3 volts for the heaters and a HV winding (± 200 Volts ac) for your HV dc to supply the 350 V dc for the valves.

Regards from across the ditch, Raymond

**Nigel Goodwin** · 7th April 2008, 11:48 AM

Quote:

Originally Posted by RODALCO

Where do you need 5 volts for in a valve amplifier ?

Some really old valves used 5V heaters, but it sounds a bit unlikely in this day and age?.

RetiredHAL · 7th April 2008, 12:49 PM

JJ
Just in case you have not yet made up your mind look at http://www.drtube.com/guitamp.htm. They have lots of little guitar amps schematics (mainly from the 60's 3 and 4 valve jobs. Some very simple and also some very sophisticated ones
Also http://www.vintage-radio.net/ is a very helpful website when it comes to valve type amps, if you are having problems.

Cheers RH

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7th April 2008, 10:14 AM	(permalink)
jjac7212	stepdown transformer Hey guys, im from australia and am trying to build an american guitar amp anyway i have a problem with the transformer and just needed to know two things. one is that my local store sells a good transformer that gives pretty decent compatibility with the circuit in terms of voltage, it takes the 240 volt aus power. the two bottom taps are 15v and i need a 5v and a 6.3v for these, so how would i calculate the right resistors for these taps to connect to, to bring the voltage down to the right value? secondly, would it be easy for a noob like myself to wire up a transformer myself? im trying to save a little money and get the voltages closer.

7th April 2008, 10:45 AM	(permalink)
RODALCO	It looks that you have a valve amplifier with 6.3 volts ac for the heaters. Normally they are fed from a dedicated 6.3 Volts ac winding of the TX. You can use a 5 Volts regulator (7805 or 7805 + 2 diodes in series on the negative to get 6.2 volts, for the valves, or an LM 317 and set it for 5 volts or 6.3 volts but it would be very inefficient. E.G. 1 Amp at 15 - 6.3 Volts 8.7 volts = 8.7 watts dissipated in heat. It is better to have for the valves a dedicated 6.3 volts ac winding. Also a transformer gives ac which you will need to rectify to dc via a bridge rectifier, and filter capacitor. __________________ There are more ways to get to Rome. Electricity, Electric clocks, Meters and Trains are great.

7th April 2008, 11:45 AM	(permalink)
RODALCO	Valve amp ? Where do you need 5 volts for in a valve amplifier ? I was pondering about that one over the last hour. Normally 6.3 volts for the heaters and a HV winding (± 200 Volts ac) for your HV dc to supply the 350 V dc for the valves. Regards from across the ditch, Raymond __________________ There are more ways to get to Rome. Electricity, Electric clocks, Meters and Trains are great.

7th April 2008, 12:49 PM	(permalink)
RetiredHAL	JJ Just in case you have not yet made up your mind look at http://www.drtube.com/guitamp.htm. They have lots of little guitar amps schematics (mainly from the 60's 3 and 4 valve jobs. Some very simple and also some very sophisticated ones Also http://www.vintage-radio.net/ is a very helpful website when it comes to valve type amps, if you are having problems. Cheers RH