Please recommend a full bridge rectifier

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oughtsix

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Joined 2009
#1
I picked up 4 of these 208v:82v transformers for $26 each.
GE Electrical Distribution e-Catalog

I think I should get about 48v out of these when running them on 120v.

SPECIFICATIONS
Category Control Power
Phase 1
PriVoltage 208
SecVoltage 82
KVA 1.5 KVA
Coil Material CU
TempRise 100 °C
ElecShield N
SubType CONTROL LEADS OUT
Frequency 60 Hz
UL Yes
FrameSize 14225
cUL Yes
CE No
Width 6.81 in
Depth 6.31 in
Height 5.81 in
TempClass 180 °C
AmbTemp 40 °C
InsulSys IS-12
EnergyEfficiency None
KFactor K1
Enclosure Type None
Sound Std
GSA Compliance No
GO Schedule TQ
List Price $191

I want to make a power supply for experimenting with all the different Class-A amp boards available on the market. I was planning on using a Variac in front of these to make the output voltage adjustable. Next pieces will be 4 full bridge rectifiers.

Is there anything I should look for in a rectifier for an amplifier power supply? I love using surplus parts when available!

I was going to start with an unregulated power supply then maybe look at the generic regulator board on the store portion of this website.

Should I pick up some of these for cheap easy filtering?
Screw Type Bipolar Power Line EMI Filter Silver and Black AC115 250V 20A | eBay
 
#2
Running a 208v transformer at 120v will greatly weaken the magnetic flux in the transformer. The output voltage will droop quickly with load. You can test this by just putting a resistive load on the ac output and watch it fall when you add more load. The waveform will also be distorted.
 
#3
powerbob said:
Running a 208v transformer at 120v will greatly weaken the magnetic flux in the transformer. The output voltage will droop quickly with load. You can test this by just putting a resistive load on the ac output and watch it fall when you add more load. The waveform will also be distorted.
Click to expand...

I am aware of this and read through the article that explains this and shows the scope traces. I decided that I want to experiment and learn for myself.
 
#5
The bridge rectifier that comes in an integrated block containing the 4 Power Diodes is usually good enough.
Available in 25A and 35A versions and available in 200V, 400V and 600V versions.

All of these are fairly cheap and can be used for other uses.
The last batch I bought attracted a good discount because I bought >25 of them and I only have a few left.

For light duty where the continuous current is <2Arms, you don't need any heatsink.

For high current duty consider whether bolting to the enclosure panel is sufficient for cooling, or to attach a proper heatsink. This is especially important for big ClassA amplifiers, or a heavily used lab PSU.

That ebay link showing 10off for <$25 is for a higher specification and covers you for just about any duty you could ever require.
 
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#6
Thank you Andrew! I have done way too much reading about swapping out a standard rectifier with a fast recovery schottky rectifier making some guys old Sony amp sound better than a $10K Levinson amp...

A good plane old way over speced rectifier is what I will start with. I have been around electronics for most of my life but class A amps are new to me. Separating sound design from the mojo is difficult sometimes.
 
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