Tube simple Psu design...first attempt

I'm trying to make a decent psu for powering a pair of preamps, pultec MB1, poormans or any similar. This is my first attempt designing something for tubes, and I would like to use some spare sparts I have on the bench. Mainly a power transformer and an EZ81from and old hifi tube amp, and two 220uf,350v new caps from Tube amp doctor.

The transformer have 3 windings that were rated for 220V primary...not the actual 230VAC here in Spain. I have some measurements without load:

310-0-310
2.5-0-4.5
3.7-0-3.7

I'm learning about tube rectifiers, but something is wrong in my maths because measuring dc output from the ez81 with 7vdc on heaters, is 340vdc without filtering and load. This should be like 300vdc after that, taking in account that ez81 voltage will drop with 40mA of current, is this correct?

Well...I have made a rapid psu schematic...some help?

I suspect your readings are correct. The dc output will be related to the peak value of the ac waveform which is 1.414 times the rms value. If your secondary voltage is 310V rms then the peak is 438 volts. This seems to imply your EZ81 is dropping 100 volts which seems a little excessive.

Cheers

Ian

As Ian said, your EZ81 is likely on it's way out.  Tube rectifiers will behave this way when they start to fail.   

With a 40ma load it looks like you will have an output voltage of just below 400VDC.  This is the voltage measured directly at the rectifiers output, just before the first filter cap or dropping resistor.  You will use this voltage and 40ma (or whatever your circuit draws) to design the rest of the supply.

http://www.mif.pg.gda.pl/homepages/frank/sheets/127/6/6CA4.pdf

Cosmonaut said:

two 220uf,350v new caps from Tube amp doctor.

Click to expand...

With 310Vac, your smoothing caps should be rated at least 450V, better 500.
As Ian says, something's very wrong if you drop 100V in the EZ81.
Also, what are those resistors across the heaters windings?

Something is wrong with the tube...and then with my design.will do it again

Those resistor in filaments were for dropping a little voltage heaters...bad idea?

Cosmonaut said:

Those resistor in filaments were for dropping a little voltage heaters...bad idea?

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They would drop significant voltage only if they drew way too much current. Many transformers are designed to have nominal voltage at full load. If you want to drop the voltage, you have to draw more than nominal power, which would quickly fry the transformer.
7V instead of 6.3 is not a significant problem. Now, if you want to drop the voltage, you could use series resistors, either with one single high-power resistor in series with the whole chain of heaters (Let's say you have 6x150mA heaters, for a total of 900mA, you would need a single 0.75R/2W resistor), either with one resistor for each tube (4.7R/0.5W for 150mA), the latter being preferrable because in case of failure of one the filaments, the others are unaffected, and because it spreads the heat more evenly.

the ez81 with 7vdc on heaters

Click to expand...

Did you measure this voltage in circuit or no load?  It seems a little high.  The EZ81 will draw 1A and since the PT & rectifier were from the same hi-fi set, the PT likely has a dedicated rectifier winding.  These are usually rated spot on for the rectifier, or, 6.3V @ 1A.

Even if you had the rectifier mistakenly ran from the other filament winding, which is likely rated higher than 1A,  drawing 1A will lower the voltage a bit from the unloaded voltage reading.