AC30CC1, AC30CC2 and AC30CC2X Owner Service Information

It isn't hard to change tubes on a Korg/Vox AC30CCSeries Amp. Here is how.

Disconnect the power cord from both the amp and the wall socket.

Lay the amp face down on the floor. Remove the upper and lower backs. Removing the lower back makes removing the chassis easier, but is not totally necesaary.

Later production of the AC30CC Series amps have speaker and reverb cables that are detachable from the chassis. Pull two reverb and one speaker cable ends off their chassis mounted jacks. Additionally, unclip the red and black speaker wires from the plywood board that supports the chassis.

Earlier production models have hard wired speaker wires and non-detachable reverb leads. On these amps, you must unsolder the leads to the speakers and remove the reverb pan to remove the amp chassis.

Remove four machine screws that face the top of the amp. These go through the "slider rail." Two screws each are on the left and right skier rails of the amp, near the speakers. The screws are about 2" long, they will require lots of turns to remove.

For clarity, this is the top side of the "chassis rail." The chassis is actually resting on this strip of wood.
After the four vertical facing machine screws are removed, the chassis will then slide out of the cabinet.

Another view of the chassis sliding out of the cabinet, exposing the tubes. Pull the chassis straight out of the cabinet and set it on a work surface with the plywood "slider" supprt board facing down

There are three kinds of tubes in an AC-30CC2.

The three tubes that are mounted horizontally are 12AX7, or ECC83 preamp tubes. This tube is most likely to survive for many years without failure, but it is the only tube in the amp that is prone to become "microphonic." A microphonic tube acts like a microphone inside the amp, causing weird distorted sounds or, in extreme cases, feedback howls. I recommend Sovtek premium 12AX7 Russian made tubes for this amp.

The four matching verical tubes are the EL-84 outputs.

The largest tube is the GZ-34 rectofoer tube. Along with the filter caps, this tube converts the AC line voltage to DC voltage to operate the amplifier.

The EL-84 power tubes are secured by a retaining clip. The tube at right has it's retaining clip released. Each tube makes about 8 watts, so the combination of four EL-84 tubes give the AC-30 it's 30+ watt output.
This is the rectifier tube, a GZ-34. If your amp is blowing fuses, replace this tube, it is likely the culprit. It is held in place by a big spring loaded cap. Remove this carefully to avoid breaking the tube.
One of my customers reported that his amp made some high pitched squealing when he turned up his reverb. He also reported that the reverb was very weak. There are two reasons why this might happen to an AC30CC series amp, and you can fix either problem yourself.

The most common cause for this problem is caused by broken delay springs in the reverb pan. The reverb pan is in a vinyl bag on the inside bottom of the amp. The vinyl bag is secured to the bottom of the amp with four screws through the corners of the bag. Once the screws are removed, you can slide the reverb pan out of the bag. Remove the small screws that retain the plywood base that covers the bottom of the reverb pan.

When opened, you should see three springs that are connected to transducers on either end of the reverb pan. It is possible that one or more of the springs might be broken on either end. Broken springs will vibrate on the bottom of the reverb pan, making a rattly distorted sound in the speakers when you turn up the reverb. The picture at left shows a pan with two of the three reverb springs broken. Such reverb pans need to be replaced.

A second problem involves the red and white RCA plugs that connect to circuit board mounted jacks inside the AC30CC chassis. See these jacks in the picture at left. Check to make sure that these plugs are firmly connected to the chassis mounted jacks. If not completely down on the jacks, these plugs can cause a high pitched whine in your amp.


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Photos and editorial content courtesy Gary Hahlbeck, North Coast Music

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