Centre tap split rail supply from twin secondaries

[Puffin]

I think I am going mad! I have made many CT supplies using a twin sec transformer but I cannot seem to get this one to work.

I have a dual 55vac tranny and have joined the centre pair. when connected to the bridge I am only getting 112v between + & - and + & CT 56vdc and - & CT 56vdc. I was expecting around 75vdc per rail. What have I done wrong?

 

[audiofan]

You should show a schematic diagram of your circuit ....

Are you using filter capacitor ... ??

 

[Puffin]

I think I might have answered my own question? Should I be using 2 bridge rectifiers as in this circuit I used for Gainclones?

 

[DF96]

If you have two identical secondaries you can use them to make a bipolar DC supply in two ways:
1. Join them to make a CT secondary and use one bridge.
2. Leave them separate, use two bridges and join the DC outputs.
Any attempt to mix these two methods is likely to result in problems.

 

[Puffin]

If you have two identical secondaries you can use them to make a bipolar DC supply in two ways:
1. Join them to make a CT secondary and use one bridge.
2. Leave them separate, use two bridges and join the DC outputs.
Any attempt to mix these two methods is likely to result in problems.

I did 1. as above, but connecting the outer secondaries to the bridge (the inner pair joined to make the CT) did not result in the 1.4 dc multiplier that I would have expected. I therefore assumed that I had done something wrong. The last time I built a Gainclone PS was about 10 years ago and I think I have gone silly

 

[scottjoplin]

You were asked if you are using filter capacitors, I hope so.

 

[Puffin]

Yes, sorry I missed that one. As the filter caps follow the bridge rectifier I have so far only connected the tranny to the bridge and expected to see an increase in the dc volts.

 

[scottjoplin]

No, you won't see that until the rectified pulses are smoothed

 

[Puffin]

Oh dear, I have obviously lost what I knew in the past. Thanks.

 

[nezbleu]

Also, don't show us a schematic that you aren't using, there are an infinite number of those. Show us the schematic of the circuit you are actually measuring.

 

[Puffin]

The schematic will be as the Carlos FM circuit above. In my defence it was 10 years ago that I last built a split rail supply The easiest way to have checked would have been to open up one of my Gainclones! I will be doing that later

 

[JMFahey]

The schematic will be as

The measurements you are posting for analysis are NOT those of a future circuit but the current one.

 

[DF96]

Yes, please show us the circuit. Not all the circuits which you do not intend to build, or the circuit which you will build. Just the circuit you have built and measured.

 

[Puffin]

Yes, please show us the circuit. Not all the circuits which you do not intend to build, or the circuit which you will build. Just the circuit you have built and measured.

Please excuse my ignorance and lack of knowledge. I will make the circuit as previously posted and come back with the results. Apologies if I have wasted anyone's time.

 

[Puffin]

Rectifier board made : Readings +74 - 0 - 74. Good to go.

 

[scottjoplin]

One or two bridges?

 

[Puffin]

Just one with the centre joined secondaries providing 0v.