Help with a Tubelab SE Power Supply Transformer

[gmonno]

Hi, I'm in the way of building a Tubelab SE, my first problem is with the power supply.
Probably I as wrong ordering a Hammond 373HX who put out 350-0-350 , it is 700V ct

This would give me far more than the 400V I was intented to drive the 300b

Now what can I do before buying another transformer?

I have a choke to substitute R4, it is a 7H 200mA that may help, but I think is not enough.

Any suggestion of how to drop out the excess of voltage?
The bad choice was the -bigger is better idea.

Thanks for your help

gmonno

 

[rfengineer2013]

Hi, I'm in the way of building a Tubelab SE, my first problem is with the power supply.
Probably I as wrong ordering a Hammond 373HX who put out 350-0-350 , it is 700V ct

This would give me far more than the 400V I was intented to drive the 300b

Now what can I do before buying another transformer?

I have a choke to substitute R4, it is a 7H 200mA that may help, but I think is not enough.

Any suggestion of how to drop out the excess of voltage?
The bad choice was the -bigger is better idea.

Thanks for your help

gmonno

Use both R4 _and_ the choke to drop the excess voltage if you feel it's too high.

Gives you the option of adding another power supply filter cap if you want - something like a CLCRC filter string. The output C (last one in the string) should be your oil-film (motor) cap if you are using one.

You might have to adjust the value of R4 to drop the correct amount of voltage.

Another option is to use a valve rectifier. The valve will drop more voltage than a diode rectifier. I think he recommends using a 5AR4. If you are using the PCB this is pretty simple to implement, just means you need one more hole in the chassis for the rectifier tube.

Good luck 😎

~ Sam

 

[Miles Prower]

Look at the specs of this puppy:

373HX
369

700V C.T.
@ 403ma.

50

5V C.T.
@ 6A

6.3V C.T.
@ 9A

A 5.0V/6.0A secondary suggests it was intended to be used with parallel 5U4GBs in a full wave, capacitor input, configuration. Given that you want 400Vdc, and the 700Vct (350-0-350) secondary:

350sqrt(2)= 495Vp

95V pretty much accounts for the forward drop of the 5U4GB when operating at ~80% of its Isurge= 1.0A/plate rating.

I had the same problem crop up myself: a NIB Stancor PTX that had the right current rating, but overvolted badly with its 650Vct secondary driving Si diodes. That put out 458Vdc (unloaded) and I needed 350Vdc. It also had a 5.0V/3.0A secondary. I simply redesigned for the 5U4GB (of which I have about a half-dozen) and it works like a charm. That Stancor was likewise intended to produce 350Vdc from full wave 5U4GBs. That's what I measured: 352Vdc with 34uF (two 68uF/350Vdc in series) for a design nominal Isurge= 800mA/plate.

You could also use the voltage dropper at the bottom of the page: MOSFET Follies

 

[TheGimp]

I simulated it in PSUD II and found a 2.2uF cap followed by a 5H inductor and 220uF cap gives near 350V at 120mA load. this was with SS rectification. 7H put it right on 350V.

You can adjust the first cap value in a CLC to change the output voltage.

 

[rfengineer2013]

...(the) valve will drop more voltage than a diode rectifier. ...

~ Sam

By that I meant "silicon" diode rectifier, of course.

But then again, I think the TuneLabSE doesn't use silicon rectifiers for the HV supply anyway so "never-mind"...

(BTW - I'm in the middle of building a TuneLab SimpleSE, which can use either a 5AR4 valve or silicon rectifiers in the HV power supply. Please excuse my confusion here 😀) 😎

~ Sam

 

[gmonno]

Thanks all for help