DIY Amp Repair Basics

by revamp on July 22, 2010

If you have never been inside your tube amplifier before, there are some things to know to stay safe. Be sure that you invest some time in learning about how things work in a tube amp or bring it to us. You don’t want to fool around with amp electronics without some knowledge because you can definitely injure yourself or worse.

We’re going to hit a few of the basics here just to give you an idea of the work involved and this by no means, a tutorial. I recommend learning, hands on, from someone who is experienced in amp repair.

The ABCs:

UNPLUG your amp.
Yes, this is elementary, but good to be reminded. If you need to take a live-voltage measurement, then of course, you . Leaving it plwould have to leave it powered and be sure you know what you are doing.

Allow The Power To DRAIN:
If you just turned the amp off, there will still be high voltage remaining in the caps after you power down. Unplug the amp and allow it to drain for at least 5 minutes.

Drain Any Residual Voltage:
After unplugging, allowing a normal drain, you will need a method to suck the amp dry of voltage. A good technique for this is to connect a shorting jumper between the plate of a preamp tube and ground. A shorting jumper will pull any remaining high voltage to ground through the 50k to 100K plate resistor on the tube. You already know what pins are the plate pins, right? Be sure you’ve done your homework before starting the project.
The jumper should stay in place while you work on the amp and do not forget to remove it when the job is complete.

Test It:

Using your multimeter and ground the (-) lead, probe the high voltage caps to be certain the voltage across them is down. You want it to be less than 10V.

Close it Back Up:

Remove the shorting jumper. Look inside and make sure all tools and parts are not left behind and put the chassis back in the cabinet. You can leave the screws off if you think there might be additional work to do, but be sure everything is solidly in place. If you are happy after a listening test, put your screws in and tighten it up. If not, return to step 1.

If you are comfortable with tube amplifier electronics, go for it. If not, bring it to us at Revamp Los Angeles Amp Repair and we will make sure it’s done properly at a fair price.

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