Estimating the Load on a Pertronic 50 Watt Evacuation Amplifier


When amplifiers are used to drive evacuation systems it is often difficult to accurately know how much capacity is used or available on the amplifier – important information in fault finding or system extensions.

For Pertronic 50 Watt amplifiers, the table below has been developed to help provide this information. The only equipment required is a multi-meter – or preferably two. As the power load from the speakers increases, so too does the DC current drawn from the amplifier’s power supply. If Tone 22 is selected on the amplifier (refer to the Operating Manual), then at full load the amplifier will draw 2.5 A @ 27 Vdc.

To estimate the amplifier loading from current drawn:

(a) Set the evac tone to Tone 22.

(b) Ensure only one amplifier is connected to the DC supply.

(c) Insert a multi meter, set to amps, in series with the negative supply lead and DC supply connector.

(d) Use a second multi meter, if available, to measure the supply voltage across the DC connector.

(e) Operate the amplifier in Evac, and measure the DC voltage and current drawn – compare readings against the table to identify the loading on the amplifier.

(f) Remember to reset the Evac tone to the original setting when testing is complete!

Current Drawn

(use Amplifier Tone 22)

Supply Voltage

Amplifier Load

(Capacity Used)


0.2 A

27 Vdc

2 %

10kΩ EOL Only (no speakers)

0.25 A

27 Vdc

10 %


0.5 A

27 Vdc

20 %


0.75 A

27 Vdc

30 %


1.0 A

27 Vdc

40 %


1.25 A

27 Vdc

50 %


1.5 A

27 Vdc

60 %


1.75 A

27 Vdc

70 %


2.0 A

27 Vdc

80 %


2.25 A

27 Vdc

90 %


2.5 A

27 Vdc

100 %


2.75 A

27 Vdc

110 %


2.83 A

27 Vdc

113 %


Extracted from Firebits, March 2008.