EZ81 Load

[ruffrecords]

My normal pre-amp HT supplies consist of a full wave silicon bridge followed by a CRCRCRC filter where the C is typical 470uF and R is chosen to drop 10V at the nominal load current.

I now need to make a similar supply using an EZ81 as a rectifier. Assuming I use the correct series resistors and a 47uF reservoir capacitor, what RCRCRC network can I safely add without exceeding the EZ81 specs?

Cheers

Ian

 

[Shoog]

If you can find space for a choke - I have found there is little restriction on the uf after the choke.

Shoog

 

[azazello]

EZ81 will decrease +U, chock with resistance 40-50 ohm also will decrease, 10 ohm also/You can disconnect it.../....
Maybe You can recalculate Your filter path....for receive the same U-s from every C.

 

[Merlinb]

Ian, I think your best bet is to simulate it. You only have to be sure the inrush and peak ripple current ratings are not exceeded. It doesn't take much resistance to allow you to make the following cap quite big, quite safely.

 

[DF96]

Unless the R are unusually small and the C unusually large the only things which matter are the R and C immediately adjacent to the rectifier. The R here includes winding resistance.

 

[ruffrecords]

Unless the R are unusually small and the C unusually large the only things which matter are the R and C immediately adjacent to the rectifier. The R here includes winding resistance.

The C are typically 470uF but the load current for this project is only about 70mA so I will reduce these to 220uF. For about 10V drop in each CR stage the R is about 140 ohms. Would you consider those to be too large/small?

Obviously I will use 47uF and the recommended R for the reservoir.

Cheers

Ian

 

[Cookj]

Here's a good writeup:
Vacuum Tube Power Supply Design

Cheers

John

 

[metalking]

hi,

maybe you can try Duncan's PSUD2. it will tell you if it violates anything.

PSUD2

 

[ruffrecords]

Thanks for all the advice. Looking at the Vacuum Tube Power Supply Design article it looks like I have picked the right valve. I think I already have PSUD2 so I will definitely give that a try. It looks like a lot of inrush issues are mitigated by heater warm up so I am felling generally a lot more confident. I will work through the Schade method and see what I come up with.

Cheers

Ian

 

[DF96]

Peak current can damage the cathode. RMS current can overheat the anode. Provided your design keeps within the limits on these you should be OK. Do a PSUD2 for the datasheet PSU circuit, and your circuit. Compare limits.

 

[M Gregg]

It looks like a lot of inrush issues are mitigated by heater warm up so I am felling generally a lot more confident.
Cheers

Ian

As long as you don't get someone switch it back on immediately after power off.
I still think a choke is a better way.
It would be interesting to see if the series R and the charge current after transient doesn't cause to much sag. (depends on current draw)
Whats the volt drop on the rectifier tube?

Regards
M. Gregg

 

[ruffrecords]

As long as you don't get someone switch it back on immediately after power off.
I still think a choke is a better way.
It would be interesting to see if the series R and the charge current after transient doesn't cause to much sag. (depends on current draw)
Whats the volt drop on the rectifier tube?

Regards
M. Gregg

The sims from PSUD2 indicate that the peak inrush current will be just over 1 amp with a hot tube. Spec maximum appears to be 1.8 amps so it looks like it should be OK

Sag is not an issue as this is 100% class A.

Hammond transformer and tube arrived yesterday so I can now build and measure.

Cheers

Ian