VOX AC15 - DIY Repair assist

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VOX AC15 - DIY Repair assist

Postby JCB42 » Tue Jun 07, 2016 9:18 am

Afternoon All!

Newbie member, but in-depth reader. - So here goes!

Apologies for the long message, but I've googled to the n'th degree, to not much help and my electrical skills are not brilliant, so I was wondering if you may have any feedback before I bring go down the path of finding a Techie! $) :(

I currently own an VOX AC15C1X Valve Amplifier, bought new over a year ago. Recently it has begun exhibiting a peculiar 'clicking sound' as detailed below.

With the amp on and warmed up, all tremolo and reverb controls at zero, with the master volume and either normal or top-boost on full, the amp is quiet as to be expected.

With the volume controls on, and the tremolo controls on max the amp is still quiet as to be expected.

Only as soon as the reverb control is dialed up does the clicking begin, the higher the amount of reverb applied, the 'faster' and 'louder' the clicking becomes. Bizarrely, the tremolo appears to apply the correct effect to this clicking signal as well.

To reiterate, no guitar has been plugged in yet. As such, this seems to have singled out that my Reverb on the amp is possibly the issue.

However...!

I have an Keely Ibanez TS9 drive pedal (no true bypass), when this is plugged with a lead to the amp and another out of the pedal to effectively 'activate' the pedal the clicking returns! Even with the reverb dialed to Zero. The clicking is not as loud as with the Reverb on, but it's there. Still no guitar connected. This doesn't happen when connect my Slash Wah which does have TrueBypass.

I am not sure if this means it's a grounding issue? or what else maybe the cause?

When removing the pre-amp tube just before the two main amp tubes, this clicking issues disappears. I'm not sure if this implies its the circuitry within this area which is the root cause?

The amp has not been driven hard, its a 15W valve in a London flat, so I cant! And I'm 99% certain the tubes are fine. I've checked my pedal on a little orange Micro Terror, cables in, guitar in, max volume and gain - Silent as a mouse! So I can't blame my pedal.

So, thoughts? Any diagnostic procedures you can suggest? (???) I figure judging by the knowlege base the DIY community may be able to shed some light on it all!

Thanks in advance for any tips! (b)
JCB42
 
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