As you can hear, the bang is very evident in the video before the mod, but inaudible after. The truth is it’s probably even closer than the theory suggests, as real pots don’t curve this smoothly! I’ve done a video comparing the tone before and after the mod, to demonstrate that there’s no real difference, but who knows, you may pick up a nuance. Mathematically, the fix I’ve employed affects the potentiometer ratio only very slightly (as in the graph), I’d argue imperceptibly. The sound returns whilst the channel is still within the ‘clean’, not yet crunchy part of the drive channel turn, so all the useful elements of the gain channel remain. There is still a small bit of silence for the first part of the turn, but the very loud bang is mostly gone, with only a whisper remaining, inaudible unless you’re listening for it. However I came up with a fix that sorts some of the issues with the existing pot.
There are switches and capacitors internally that would prevent the available chassis mount parts from being suitable. Unfortunately I wasn’t been able to find an alternative panel mount part that will fit into the space constraints inside the case. Of course I tried to contact Egnater, but received no reply. It’s quite easy to find dual ganged 500K pots from guitar gear suppliers but they’re designed to fit inside guitars or in ’boutique’ hand wired amps – none of them will fit in to the space in this tiny Egnater repair. There was no maker’s mark on the pot so I couldn’t be sure what brand it was: probably a far eastern part sourced by the contract manufacturers. This caused a loud clunk at the point where the track re-appears (see the video). One half of the pot behaved fine, the other half was open circuit in the first part of the turn.
This is a dual ganged part (2 pots in one). The diagnosis itself didn’t prove a problem, the problem was simply the gain potentiometer itself. At first, I had a bit of trouble with the Egnater repair but I’m pleased to say that I found a solution for the customer. Categories Recent Repairs Tags AC30 Repair, amp repair, repair, tremolo, valve amp repair, vibrato, vintage ac30 repair, vintage amp repair, vintage amp safety, vintage vox repair, Vox Repair I’m pleased to say that the customer was very happy with the vintage vox repair! If you have a Vintage ac30, or a vintage amp in need of repair, please get in touch. This is not an uncommon task in vintage Vox repairs.Īs with the Confetti 1962 vintage ac30 repair, I hard wired the mains to 245V for UK operation and replaced the ancient power cord with a modern tri rated mains lead. The fault was with the modulation circuitry and was again down to a worn out capacitor. 2 are an audio input buffer, 2 create a modulating signal and 2 mix the modulation with the audio signal.
In vintage vox circuits, this consists of 6 triodes worth of analog electronics. This turned out to be an out of tolerance resistor in the gain stage and a faulty coupling capacitor. I found that the brilliant channel didn’t work. It was once covered in a cream vinyl, but the customer (who had it from new!) had decided at some point that it would look cooler in black and painted it.(!)Īfter laying down his axe many years ago, the customer decided to sell the amp and brought it to me to service. This is (as far as I can tell) a 1961 model. Shortly after the Confetti 1962 vintage ac30 repair arrived, this vintage Vox repair turned up on my bench too! The 1961 in the picture is on the right, the left amp is a 1970’s vintage vox, which you can read about here.
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