Power Supply Testing

[snowman]

Hi there, I was wondering how folks test their power supply mid-build.  I was hoping to check voltages and ripple of the power supply I put together without building out the pre and output sections fully.

I recently blew a 5Y3S along with potentially the 290BX PT (crackling) by what I assume is running a short or not putting a sufficiently large enough load on B+.
I have the 290BX PT plugged into the variac, the HT going to 5Y3, 5v going to the 5Y3, 6.3v secondary going to a a 6V6 and a 12AX7.  I then had the B+ going to a 200W 8ohm load resister, then to ground.  I assume this is where I went wrong, but not certain. 

I got the 120V variac up to about 60V AC before the 5Y3 fizzed blue then died with the 290BX PT crackling about 10 seconds later.  I also tested with my B+1, B+2, B+3 resistor/capacitor set in place with the load resistor at the end of the line, but that also heated the transformer too much.

Any idea on where I went wrong here?  Any help would be appreciated.

[sluckey]

B+ going to a 200W 8ohm load resister, then to ground.  I assume this is where I went wrong, but not certain. 

BINGO!

[tubeswell]

Hi there, I was wondering how folks test their power supply mid-build.  I was hoping to check voltages and ripple of the power supply I put together without building out the pre and output sections fully.

I usually just wire it up and put some preamp tubes in to load and test the heater supply, and measure the heater VAC and the B+ at the reservoir cap (and then with the stdby switch on - if there is one). If it's a fixed bias output stage I check the output tube grid pins for negative bias voltage before plugging output tubes in.

[glass54]

+1 with Tubeswell.
If you have fitted the 270k/330k 2W across your main (+B1) reservoir capacitor, then that's a "light load" along with the preamp tubes.
As Tubeswell pointed out, if you have checked voltages as per the list, and double checked the +HT to O/P transformer wiring as well as  correct Anode-Transformer wiring, you should be laughing 
You will notice say nominal  10% drop in +HT once the output tubes are fitted and they have "warmed up".
8R 200W  load is ONLY for "speaker" Load.
Kind Regards
Mirek

[acheld]

+2 with Tubeswell.

I have a set of "test" tubes that I use for this purpose, though I confess that I normally complete the build before testing voltages.   

[mresistor]

  I was hoping to check voltages and ripple of the power supply I put together without building out the pre and output sections fully.

Why?

[shooter]

not sure the OP's why, mine
I've always build in stages/"modules";
PS, test
Front end, test
main body, test
output, test


mainly "finds" the self-inflicted mistakes before it becomes a behemoth
comes in handy in both digital and analog "systems"

[snowman]

I appreciate all the input.  I have a pretty good idea of what to do and not do at this point.

As for the why, mostly curiosity.

Thanks.

[mresistor]

not sure the OP's why, mine
I've always build in stages/"modules";
PS, test
Front end, test
main body, test
output, test


mainly "finds" the self-inflicted mistakes before it becomes a behemoth
comes in handy in both digital and analog "systems"

thanks  but honestly  I didn't ask you why .

[HotBluePlates]

...  I was hoping to check voltages and ripple of the power supply I put together without building out the pre and output sections fully.

... I have the 290BX PT ... the HT going to 5Y3 ...  I then had the B+ going to a ... load resister, then to ground.  ...

Your original post indicated you had at least one output tube in place.  But let's assume you had no tubes installed.

The 290BX has 330v output, and normally powers a pair of 6V6s.  330v x 1.414 = ~467vdc but the 5Y3 will likely drop that to about 405v.

If the 6V6s were idling at 100% dissipation they would draw 12w / 405v = ~30mA each.  Double that for two 6V6s and add another 10mA for screen current.  So the 6V6s oughta be pulling about 70mA from the power supply.

---------------------------

405v / 70mA = ~5.8kΩ
405 x 70mA = 28.35w

So maybe something like a pair of 12kΩ 25w resistors in parallel? (They would still need to be mounted on a heatsink to realize their "25 watt" rating)