Power Up; Working Inside A Tube Amplifier Safely; Unplug; Sit - Trinity Amps THOR Builder's Manual

Power Up

*** RE-READ SAFETY WARNING AGAIN! ***

Working Inside A Tube Amplifier Safely

Working inside a tube amplifier can be dangerous if you don't know the basic safety practices. If you
aren't prepared to take the time to learn and apply the right precautions to keep yourself safe, don't
work on your own amp. You can seriously injure yourself or get yourself killed.
Pretty self explanatory. Do not, ever, ever, leave the equipment plugged in and start work on it.

Unplug

Leaving it plugged in guarantees that you will have hazardous voltages inside the chassis where you are
about to work.
If the amp has been turned on recently, the caps will still have some high voltage left in them after

Sit

the switch is turned off. Let it sit for five minutes after you turn it off.
When you open up an amp, you need to find a way to drain off any residual high voltage. A

Drain

handy way to do this is to connect a shorting jumper between the plate of a preamp tube and chassis
ground. This jumper will drain any high voltage to ground through the 50k to 100K 2W plate resistor
on the tube. To do this successfully, you will need to know which pins are the plate pins. Look it up for
the amp you're going to be working on. You'll need to know this for the work anyway. Leave the
jumper in place while you do your work. Remember to remove it when you finish your work. You can
also permanently install a 220K 2W resistor on the B+ line to chassis ground to do this.
Take your multimeter and ground the negative, black lead to the chassis. With the positive, red

Test

lead, probe the high voltage cap terminals or leads and be sure the voltage across them is low.
Preferably to less than 10V.
First take the shorting jumper out. Put the chassis back in the cabinet, making sure all of your

Close

tools, stray bits of solder, wire, etc. are out of it. You don't have to actually put all the screws and so
forth back in if you believe more work might be needed, but make sure that the chassis is sitting stably
in the cabinet and won't fall out.
First note that most meters have three input jacks (some have four) one is marked COM, the BLACK
lead goes there. Another jack is marked V, ohm, mA, the RED lead goes there for most measurements.
The third jack is a high current jack usually marked 10ADC (sometimes it is 20 or some other number).
This jack is used only for high current measurements. The four jack models use separate jacks for
current measurements, this makes accidentally setting the meter to a current mode harder, but it still can
be set to resistance. For vacuum tube electronics we can usually ignore the high current mode. Put your
test leads into the COM and V(ohm)mA jacks and leave them there.
Trinity Amps THOR Builder's Guide. Version 21.2
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