Harley Benton GA 15 Ultimate Mod Kit Manual page 3

Hide thumbs Also See for GA 15 Ultimate Mod Kit:

- Cosmic Ampworks

- The Ultimate Harley Benton GA15 Mod Kit- Version 1.4 - 200127

2. Safety

2.1 Safety warning

Always unplug the amp before doing any work on it.

A tube amplifier chassis contains lethal high voltages

even when unplugged

- sometimes over 500 volts DC! If you have not been trained to work with high voltage

then have an amp technician service or modify your amp.

High voltages in a tube amp don't disappear directly after you unplug the unit's power chord.

The internal filter

capacitors can store lethal voltages for days or even weeks. Before working on the GA15, it must be ensured

that the amp is unplugged and that these filter caps have been de-charged. The filter caps in the GA15 look like

little black cylinders (Figure 2). The encircled row of 3 large capacitors (Figure 2) are the ones that supply HT

(High Tension!) power to the electron tubes, hence these are the most dangerous ones. But... you can't easily

see what parts are connected to which filter caps - so maintaining the highest level of caution AT ALL TIMES is

required! There is only one way to verify that the filter caps have been drained and the amp is safe to work on:

by checking for remaining voltages with a multimeter, after having switched off and unplugged the amp.

Figure 2. Filter capacitors and most parts of the HT (High Tension) section of the Harley Benton GA15 printed circuit board (seen from the

back of the chassis).

2.2 How to - safely - measure voltages in a GA-15?

Never touch the amplifier chassis with one hand while probing with the other

hand. Use just

one hand

when

working on an amp that potentially still contains high voltages.

Also, wear safety goggles, in case you

accidentally cause a short circuit!

Ideally, your multimeter has a clip-on ground probe that you can attach to the (negative) grounded chassis.

You can then use one hand to carefully measure voltages in the circuit with the positive (red) terminal of the

multimeter, keeping the other hand in your pocket, away from the chassis. To ensure that you don't

www.cosmicampworks.com

Dedicated to the Advancement of Stellar Tone!