Tube amp power supply question.

[Johnblue]

I need to deliver 410v (under load)  B+ to the plates.  I'm using PP 7868 tubes. And 10k output traffos.

The power transformer I have is 250-0-250 CT

Can I get the 410v ?

I SS rectified and got 350v I'm struggling to find a decent way to  use this transformer.

I'm kinda failing on a "voltage doubler" with the Center tap attempts.

Can I just ignore the center tap?  Ground the center tap? What would happen then?

Should I just get a better suited power Traffo?

The transformer is beefy, it can handle a doubler, I just can't find the correct way to do it with a CT

 

[ruffrecords]

Your best bet is to get the correct transformer.

The 350V you are seeing now from the 250-0-250 transformer is the no load voltage. To determine if the transformer is up to the job you should really add a chunky sized resistor across the output that will take the expected load current. Leave it running for an hour and see how warm the transformer gets. If it stays cool or gets warm it is OK. If it gets hot it is not.

Do you know the current rating of the 250-0-250 winding?

Cheers

Ian

 

[Johnblue]

I don't know exactly what the current rating is, but the Vintage HI-Fi console I pulled it from, housed stereo 6bq5 amplifier, its preamp and had an umbilical cord that also powered an entire 12-tube radio,Tuner and phono preamp. Its a sizable power transformer.

I'm trying to use it to power a stereo homebrew barebones 7868 power amp, its going to need at most 190 mah. And that's max-max

I get what you are saying though. I probably should just get a better  power transformer.

 

[ruffrecords]

There is a design for the EL506, wich I believe is equivalent to the7868 that generates its HT supply from a transformer with a 320V secondary so maybe that is what you should go for:

http://www.r-type.org/exhib/aaa0711.htm

Cheers

Ian

 

[PRR]

> I probably should just get a better  power transformer.

Or use it the way it was meant to work. Two 18-Watt channels working ~~340V at 10K load each. (The tuner load is trivial on top of this.)This can be EL84/6BQ5 working at ratings, or 7868 worked some below ratings, or 6V6 worked hard, or 6L6 worked easy. If you play, one 35-40W channel working 5KCT load.

A doubler (actually a FWB no-CT) leads to about the same power at twice voltage, half current, and 4X impedance. 680V and 40KCT are not common tubes or windings.

 

[Johnblue]

Thanks guys I scored a hefty looking 350-0-350 transformer at auction for $40 .. It also has a 30v bias tap which will make my life easier too. This should give me plenty to work with. And now I won't have to "double" and then Drop and waste energy.

I'm trying to loosely copy the output circuit of "the fisher 400" reciever amp.

It all started with the pair of 25w 10k stancor output transformers that I had laying around. They are good iron, with 4-8-16 and 500 ohm taps.

There's not many documented circuits with 10k OPTs that are 20w  ... I figured the Fisher was the way to go, the hi-fi guys have all types of mods they do to them.