GC Split Rail Supply

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Puffin

Member
Joined 2006
I have re-built a power supply to power some bridged GCs that I built, tested and never used. Basically it is to tidy things up so that I could safely use the amps.

The Trannys are 300va 25 + 25 AC. I was using Carlos Filipe's schematic for the original rectifiers and seem to remember that each rail was around 42 - 45vdc (just within the 3886 limit)

To tidy things up I have used some generic rectifier boards. The resistors are 2.2k between rails and 1R elsewhere. There are 2 R1's on each rail (one under the board on each side)

I am getting roughly 51vdc after rectification which is too high. I asssume that I could reduce this by changing the resistor values. Am I correct?

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
P

Puffin

Member
Joined 2006
Primary wiring (details on side of tranny) Blue, Grey, Violet, Brown. Blue and Grey one pair, Vio and Br 2nd pair. For 240v you join Grey and Violet.

Dual primaries should show ~240Vac across the series pair.
Then show ~120Vac across each single primary.

Bulb not lighting, or do you mean when checking the primaries as above? I am not clear as to how you are suggesting I measure.
 
A

AndrewT

R.I.P.
Joined 2004
with dual primaries all four ends are available to measure voltages.
measure across one primary winding.
Now measure across the other primary winding.
Now measure across the series pair of primary windings.

You should see readings of ~120Vac, ~120Vac, ~240Vac.

The bulb off indicates you have not wired the primaries out of phase.
 
JOHN BALI

JOHN BALI

Member
Joined 2010
Bulb tester

Hi Puffin,
I guess this is what AndrewT suggest to you
Make sure the load is greater VA than the bulb...

Do you use 1 or 2 trafo for this GC?
If you try to use 2 trafo & it is 2x25 Vac
then if you connect it like the schematic it will be 2x50 Vac because maybe you not use the ct of the trafo...
btw have you measure the secondary, it is 25 ct 25 right?

On the schematic that use 2 trafo & single 22-24 Vac
if your trafo has dual secondary eg 0-25 & 0-25, why not build dual mono amp


Regards
 

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P

Puffin

Member
Joined 2006
John. Each tranny has dual seconarys. The centre pair are joined to make them CT. When the ac secondarys are tested they are showing 35vac.

Andrew T is suggesting I check that I have the primaries correctly wired. I will do this today.

I have been using a light bulb tester for many years.
Regards

Rob.
 
A

AndrewT

R.I.P.
Joined 2004
AndrewT said:
The bulb off indicates you have not wired the primaries out of phase.
Click to expand...
If dual primaries are wired correctly the bulb will stay off if nothing else is connected to the transformer DUT.

If the primaries are paralleled and out of phase, the bulb will light full bright.
If the primaries are seriesed and out of phase, the bulb will light full bright.

That's why I keep reminding Members to always use the bulb for mains testing.
 
JOHN BALI

JOHN BALI

Member
Joined 2010
AndrewT said:
measure across one primary winding.
Now measure across the other primary winding.
Now measure across the series pair of primary windings.

You should see readings of ~120Vac, ~120Vac, ~240Vac.
Click to expand...
Hi AndrewT, good suggestion I also must remind it :)

I know AndrewT suggest this to ensure that trafo is normal at primary

Blue and Grey one pair --- measure here should be 120Vac
Vio and Br 2nd pair --- measure here should be 120Vac too
Blue and Br --- measure here should be 240Vac

If the reading 120Vac is not same than your primary must be damage

I will suggest you the reverse way if you have another trafo that is normal & output 0-25 volt. Connect it to one of the secondary of your trafo & measure all another primary & secondary.
If you find that one of them not similar....:cool: your trafo is really in big trouble
 
P

Puffin

Member
Joined 2006
AndrewT said:
with dual primaries all four ends are available to measure voltages.
measure across one primary winding.
Now measure across the other primary winding.
Now measure across the series pair of primary windings.

You should see readings of ~120Vac, ~120Vac, ~240Vac.

The bulb off indicates you have not wired the primaries out of phase.
Click to expand...

I have been doing a bit of head scratching about this. I have definitely got the primaries wired correctly for 240v (Grey & Vio joined) Br & Bl connected to 240v. Would I be riight in assuming that I should connect one set of primaries (Bl & Gr) to 240v and then measure the other pair (Vio & Br ) and then vice versa (each pair should measure 120v)?
 
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