Amplifer repair tips

Electrical safety

WARNING! VALVE AMPLIFIERS AND ELECTRICAL SAFETY!

Valve amplifiers can be VERY dangerous to work on (as is clearly implied by this bold red text) if you do not have knowledge of electrical concepts. If you are not sure of what you are doing then take the amp to a qualified technician.

If however, you do want to learn to how to safely poke around in your own amp (with a chopstick of course)or even build one or two then start off with lots of reading first. It's best to get your hands on as much material as you can, both printed and online. Don't worry if you don't understand it all at first, you'll realise that as you learn about similar concepts explained in different ways the lessons start to sink in and knowledge begins to develop...

The following are a few tidbits of knowledge gleaned from my time in the business, both repairing electronic equipment and playing bass guitar in bands.

Lending gear

Always be careful about who you lend your gear to. I know, I know, you don't want to seem like a scrooge but it's that one time you get really burnt that ruins it for everyone. My general rule of thumb for making my bass rig available to other bands on the same bill is if they've had the courtesy and common sense to organise it all beforehand then I'm much more comfortable with it. The classic scenario is when someone turns up to a gig without an amp and asks "hey it's ok for me to use yours right?" It generally prompts the answer, "Oh, you know what? I was going to ask you the same thing, damn, looks like we're playing through the PA tonight."

At the end of the day it's your gear but my advice is to exercise some caution.

Fuses

Always unplug an amplifier before checking or changing a fuse. Some amp designs, particularly older ones have one end of the fuseholder connected directly to the AC mains input. This means that even with the amplifier off, one end of the fuse is still in contact with the plug. Always use the specified rating and type of fuse. Using a higher rated fuse can cause your amp to go up in smoke while the fuse remains intact. The best seen here so far was a 17 ampere fuse in a 100W Eminar. Yes, a 17 amp fuse...Beaten only recently by the amp technician's holy grail of fuseholder finds, the cigarette packet foil paper wrapped around a blown fuse.

Servicing

Getting an amplifier serviced keeps it running properly and makes detecting any problems before they potentially become catastrophic an easier task for a technician. Servicing keeps pots working quietly and generally involves a clean up of the control panels and tolex. If you take your gear to the same trusted technician time after time a 'relationship' develops between the technician and the amplifier (nothing untoward I promise) which allows the technician to maintain your amp in top condition and understand individual nuances peculiar to your gear.

Standby switch

The standby switch on your amplifier is mainly there for the purpose of givng the valves a chance to warm up before being hit with the high voltage component of the amplifiers power supply. With the amplifier in standby mode, the filament voltage is applied to the heaters in order to get them to the required temperature for electron flow to occur. Switching the amp out of standby mode then allows the B+ and bias voltages to be applied to the valve, meaning that the valve has had a chance to warm up before doing any work. This can increase valve life marginally by avoiding a condition called 'cathode stripping', where the valve begins to conduct before it has reached optimal operating temperature. Bear in mind however, that this condition is involving very short time periods. Whilst it's a good idea to use the standby switch at startup, your amplifier isn't going to suffer if you forget every now and then. Definitely the most useful feature of a stanbdy switch is to mute your amp between sets or during breaks at band practice.

Stubby holders

Stubby holders double reasonably effectively as hot power valve pullers. Use 'em if you have to pull out hot power valves.

Chopsticks

Or totally plastic pen like a sharpie etc, one of the most useful tools available to an amp technician. Extremely useful for poking, prodding and banging live circuits safely. Exceptionally useful for locating the general area of cold solder joints in Fender Hot Rod Deluxes.

Don't wait

If your amplifier is displaying aberrant behaviour take it to a technician. The nature of repairing electronic equipment, particularly old electronic equipment often necessitates careful monitoring of work to ascertain correct operation. This process alone often involves time spent with the amp idling. Not to mention any time required to source unique parts for a particular repair job. Don't wait until 3 days before a gig to take a broken amplifier to a repair technician! If you want me to bake you a cake in one day I can probably promise that but don't expect miracle turn around times from amp techs unless they specifically advertise them.

As a counter point to this, don't ever tell a technician, "there is no rush", you'll never see your gear again.

Knobs

Please, please don't ever glue knobs on to potentiometer shafts. It makes it really difficult to later conduct repairs if the pots need to be removed.

Masking tape

Please don't stick masking tape on your amp unless you intend to take it off agan within a short period of time. Masking tape left on for any extended period of time creates a truly unique sticky gooey mess.

Fender combos

If you want the rear panels of your Fender combo to stay in reasonable condition exercise care when carrying the amp to make sure the upper rear panel is not bending against your hip or leg. I see so many broken and bent ones due to this scenario.