SEX 4 Power Transformer Voltages

[pevelg]

Hi,

I've started building my SEX 4 kit and am at the testing of the Power Supply Board Testing.

For the 6.3V DC pads, I am getting -4.29 V for both pads, which is within spec (+/- 3.5V - 4.75V)
For B++1, B+1, B++2, B+2, I am getting 493V, which is above spec (420V - 450V)

Perhaps relevant prior measurements:

Powerline AC Voltage: 123.4V (used terminals 18 & 15 for white wires going to 44U)
Power Transformer Terminals 7 & 8: 6.61V
Power Transformer Terminals 11 & 12: 178.7V

I've keep looking through the manual but can't seem to find any obvious mistakes. Including some images for reference.

p.s. Not sure if it is a misprint, but the PCB on power transformer shows 16V for the 10,000 microF capacitor, while manual and provided part states using a 10V 10,000 microF capacitor.

 

[Paul Birkeland]

That's reasonable enough, they will drop when the rest of the circuit is built out and drawing current properly.

 

[Jameson]

We’ve been discussing widening that range in the next version of the manual, too. It’s on the list to get done soon.

 

[mete]

In the Power Transformer Secondary Test (mains is 230Vac, I measured 232Vac), I am reading V_9_7=6.9Vac, whereas the range is given as 6.3Vac and 6.8Vac. Maybe that range should also be updated. V_12_11 is within range 185Vac.

 

[mete]

Even worse than pevelg, I read +-4.5Vdc on heaters, but 511Vdc and 513Vdc on B+ points. I understand this might still be OK (if 490Vdc is OK, is 515Vdc also OK?) as the circuit is completed, but the capacitors are rated 450V, can the test be dangerous for the capacitors ?

 

[Paul Birkeland]

232V on the 225-235V winding configuration should land you under 500V on the initial turn-on test.

Electrolytic capacitors are generally OK experiencing a turn-on surge voltage provided they get some run time at their intended voltage after the surge. For what it's worth, we have put the same 22uF/450V caps in that position in SEX amps for 19 years without any failures that I can remember.

 

[mete]

You said it should be under 500V for 232V, is there something I should do or shall I continue the build ?

 

[Paul Birkeland]

Can you post a photo of the wiring of your power transformer?

 

[mete]

 

[mete]

Maybe I should modify it to use 235-250Vac wiring, would it decrease B+ and 6.3V too much ?