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CREE rectifier bridge

daveinnz

daveinnz

New Member
Wise people of the Forum....

I'm looking to upgrade the power supply on my Tube amp. The supply, while adequate, sags under load. The supply is a traditional transformer to SS bridge rectifier to cap / choke / cap combination.

In reading some forums there is a suggestion that upgrading the bridge rectifier to a CREE Schottky Diode (fast recovery) configuration helps in the process (as well as upgrading with better quality caps and choke of course.

I can't seem to find a CREE diode bridge configuration on the market - square with 4 pins or lugs. There appear to be plenty of CREE diodes available, and some smart person has put them on a circuit board here and here , to make a bridge rectifier, however, I can't find them in one unit.

Has anyone found a source for these?

Thanks
 
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Changing the choke and diodes won't change much, unless you intend to reduce the value of the choke, but then you get less filtering. Increasing the cap values might help, but you can also go to far and really mess up the amp. The real culprit is probably the power transformer. What's the amp? Do you have a schematic?
 
Hi
I'm working on a Cayin A88T. For all the hard comments that get thrown at Chinese amps , this one is really well built and has some good componentry, however the coupling caps are in for a replacement with some good Mundorfs (!) Schematic is attached.
It's running Svetlana 's 6550's on the outputs, Tung Sol 6SL7GT's and Sylvania 6SN7GT's in the driver stage.
 

Attachments

Can you describe the power supply sag you're seeing? I would expect those 470uF caps on either side of the choke to hold the voltage steady over a relatively long time period. BTW, I recommend that you add a 150KΩ resistor from each of the bias pot wipers to the top of the pot. That will prevent loss of bias if a wiper momentarily loses contact.
 
Sag from idle to sustained full power is impedance in the supply, mostly transformer but the choke will add some. Choke part is easy, just measure the DC resistance. If its too much, sub it for one with less DC resistance but broadly speaking chokes of a value at a current all measure around the same. Its just a thing you get based on turns and wire size.

The transformer is the ratio of primary to secondary voltage squared times the DC resistance of the primary plus the DC resistance of the secondary. The only thing you can really do about it is to replace the transformer and honestly that isn't practical in most cases.
 
daveinnz said:
Wise people of the Forum....

I'm looking to upgrade the power supply on my Tube amp. The supply, while adequate, sags under load. The supply is a traditional transformer to SS bridge rectifier to cap / choke / cap combination.
Click to expand...
Has the amp always had sag issues? Or is it more apparent lately?

How old are those main power supply filter caps?

A close-up photo of the circuit layout would be groovy buckets! :thumbsup:
 
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