WOA Meters.

[George S.]

Built up a set of meters today and need help translating engineer speak to hobbyist. The wiring looks straight forward but want to make sure I understand the calibration for a 400.
Calibrate one channel at a time. Attach a True RMS voltmeter to the output. Make sure the amps attenuator is set for highest output.
Set my signal generator for 500Hz sine wave at 3 volts amplitude. Connect the signal generator to the channel I'm calibrating and turn on the amp while watching the volt meter.
Slowly bring the sine wave amplitude up until I see 40Vrms at channel output, which should be appx 3.198298 volts peak to peak amplitude on the signal generator.
At this point adj the boards 10 turn pot to just illuminate the 31st segment.
Is this correct? Want to possibly get these installed next weekend.

 

[George S.]

Wait, measuring at amps outputs can't be right. Has to be a test point on the board I haven't noticed. Going to bed.

 

[FredR]

Measuring at outputs is correct.

 

[laatsch55]

I would say drive the amp to rated output and adjust to 0db. .

 

[George S.]

Thanks guys. I'm concerned about driving the amp to 40 Vrms output without having a load bank on the outputs. I started thinking maybe I'm supposed to connect the volt meter to the meter wire that comes off the back plane, but connection at outputs makes more sense. Just that the instructions say no load on the outputs. Guess the volt meter is high enough impedance it won't count as a load?

 

[mlucitt]

Guess the volt meter is high enough impedance it won't count as a load?

True. Properly working Phase Linear amplifiers (with or without WOPL upgrades) will tolerate full power with an input signal up to 3V as necessary to obtain 40VRMS at the output.

 

[George S.]

Thanks Mark. Cool. I'd be really bummed if I shorted it or over heated it. Thank you!!!!! A question occurs. Since I'll be inputting a pure sine wave, does the volt meter really need to be a True RMS? I have a old Radio Shack True RMS multimeter, and a old Fluke 77. Both have correct fuses and seem to work properly with very close results between the two. Are one of these sufficient or do I need to go shopping?

 

[laatsch55]

An Heorgw, they'regood. I had an old Craftsman 29 dollar meter and it tracked well with 179...
George I hit 1.1kw on my AP one time in 4 ohm mode on a 700 B....just cause...had never seen the "kw" scale come up..

 

[wattsabundant]

The P/L tech manuals should be a must read before starting any upgrade project. See the attachment.

 

[George S.]

Lee, cool, I'm good to go! Don, thanks, that explains it all in a nutshell, never saw that before. Need to print that manual out for reference. Thanks guys! D'oh!

 

[Gepetto]

George
Don't follow the original PL instructions. Those are for the original meters. Follow what is printed out in your photograph

 

[George S.]

Joe, I understand. Will do. Thank you.

 

[wattsabundant]

The P/L tech manuals should be a must read before starting any upgrade project. See the attachment.

Sorry for the confusion. Bad assumption on my part. Assume = ass -u-me.

 

[George S.]

Hey Don, no problem, you did good showing me that info. That's good info to know. I was really hesitant about attaching a volt meter to the outputs, and then driving output to 40 volts. To me and my limited knowledge, this just didn't sound like proper procedure. You showed me it is proper, it's in the manual. That's a GOOD thing to know. Knowing what's in the manual now makes Joe's instructions clear. I was lacking that basic info you supplied. Thank you!!!!

 

[mlucitt]

I hit 1.1kw on my AP one time in 4 ohm mode on a 700 B

A WOPL 700B, I assume. Not bad for one channel...

 

[laatsch55]

Yeah, pretty clipped though..

 

[laatsch55]

No load...AP on 4 ohm scale...

 

[Gepetto]

Hi George
The amp doesn't care at all that it is driving into no load. It just views that as an easy day of work....

 

[George S.]

Joe, got it. Based on my experience with 10 and 11 meter mobile transceivers, one never transmits without a dummy load, or proper coax and antenna. This is why I was so hesitant. Thanks, will probably get them installed this weekend.

 

[mlucitt]

Some amps do generate a lot of heat on the output transistors with no load. This is one of the reasons Phase Linear was so popular with the bands. I cannot count how many times I forgot to plug the amplifier into the speaker cabinet. Duh.