SPP Transformer question

[1108]

Would a 660 vct transformer work for the SPP? I know it's a little more than what's recommended.

Edcor XPWR178-120

https://www.edcorusa.com/xpwr178

 

[JonSnell Electronic]

It is a mains transformer and has no air gap to stop it from saturating.

 

[1108]

I'm not sure what you are saying. Yes I know it's a mains transformer. Tubelab recommends one that is 640 to 650 vct for the SPP. The edcor is 660. My question is can I use it?

 

[JonSnell Electronic]

No. There is no air gap for the DC bias current that a valve needs to work. The transformer will saturate (magnetic field) and stop working. If you had no DC current through it, it would be fine.

 

[1108]

So I'm trying to understand this.....
Because of no air gap, ("There is no air gap for the DC bias current that a valve needs to work") are you saying this isn't suitable for any tube amp or just this one (or one similar)

 

[PDL]

I cannot contribute as to where your b+ will come out at or wether it will be too high, but that will work as a power transformer. There is no direct current going through the power transformer.
Direct current will be absorbed by the OUTPUT TRANSFORMER, which will need to have a correct air gap to deal with this. But, the power transformer will only see an AC load. No air gap will be needed, nor would you want one.

 

[1108]

Thanks PDL. That goes along more with the limited knowledge I have. Hopefully someone can chime in about the B+

 

[PDL]

Duncan Amps PSUDII can be helpful for modeling your power supply. I used it for my SSE, and the results were spot on.

 

[zman01]

1108,

Do you already have this power transformer?

Please refer to post #574 of following thread - 660vct will be on the high side probably:

http://www.diyaudio.com/forums/tubelab/148694-tubelab-simple-p-p-58.html

The Hammond PT rknize mentions (Hammond 373CZ is 650 vct).

 

[1108]

Yes I do already own this transformer. Looks like it's a little to much for this.
Thanks Zman.

 

[zman01]

Do not give up hope.

Link for PSUD2 mentioned by PDL earlier:

PSUD2

However I have no experience with this software... I am assuming you can simulate with different values of B+ - give it a try - by changing some values of components you might get in the ballpark of running some JJ EL84s with your PT.

 

[denny3249]

PSUD...

I have used this software to design several power supplies including the one for my TSE with type 45 tubes and my SSE. It was easier than trying to work with formulas that I learned 50 yrs ago with the actual build results being within a couple of volts of what the program predicted. Take a little time to learn how to feed-in/change different component values and you should come up with a circuit that will let you use the PT you have.

 

[1108]

Thanks guys. Looking over the software now.