What is the Opposite of Voltage Sag?

[mlucitt]

Hey Lee,
I was thinking devious thoughts. Ya know how we like to find "hot" transformers, and how the output of the amps will drop if the line level goes below 117 VAC...

What if we hook up the power line cord to our VARIAC and raise the power, to say, 130 VAC. I would think that would be within the tolerance of the components, right? The kids who do amplifier competitions run their 12V amplifiers to 18V (a 50% increase) and they get mad levels of power into 1 Ohm of speaker loading, probably at 1-10% distortion and 150 db. Not that we are trying to do that. Are we?

I can try it tomorrow on a WOAPL 700B. I imagine the fuse would be the weak link at 10 Amps. That fuse would limit the power draw to 1300 Watts, up from a theoretical "normal" of 1170 Watts from 117 VAC. My VARIAC maxes out at 143.4 VAC. The label says it is good for 1.4KVA, the rated voltage at 10 Amps. I know I've got a 15 Amp fuse around here somewhere.

I'll make a measure of the rail voltages with the VARIAC turned up after I disconnect the WOA driver board. I wonder how much abuse the board could reliably take above +100 VDC and -100 VDC, do you think Joe planned for such devious thoughts? The regulators would keep the voltage low for the front end but Q5 and Q10 would feel that additional voltage, but they are 350V devices anyway.

Thoughts?

 

[orange]

Don't know but...

I suspect you'll need a push-up transformer for that.

 

[Gepetto]

Mark
Replace the TIP31C and TIP30C with MJE15032 and MJE15033 respectively if you are going to try such experiments. You are eating into the intended design margin of these 2 devices by raising the primary voltage as you are indicating. The next weak link will be the SOA rating of the primary output devices.

 

[mlucitt]

Joe, I see what you mean. The TIPs are 100V devices (and cost $0.42ea) while the MJE15032 is a 250V device (and costs $1.19ea). I'll put a few pairs on order. I don't want to smoke a board, a few outputs would be OK, I have many old ones to choose from.

 

[Gepetto]

Hi Mark
In my quest for constant improvement and highest quality, I have changed the BOM for the Q1 and Q2 devices to the ones I listed. Even though these devices only see 80V in operation and are well within the SOA rating, I ran into one bare board user that populated these locations with a brand other than the ON Semi that I use exclusively (in the BOM and in the kits and assemblies) and experienced a failure. At that point, I said, "that's it" and out came the TIP31C and TIP30C and in went the MJE devices. That choice makes it imperative that they are ON Semi as these 2 devices are only made by them. My documentation has been updated to reflect this.

 

[mlucitt]

Good call, and worth the added expense to me.

 

[laatsch55]

That was my 3rd board with the 32's and 33's in them. I have also toyed with the variac idea, but I also have some 169vct toroiods if ya wanna get real nasty.

 

[laatsch55]

BTW, kinda cool having a regulator you can also drive with!!