Vintage Vox AC30 repair – Ampworks, Newark

Culprit - Vintage Vox AC30 repair

Now, is it good things or bad things that come in threes? It must be good things. This was the third of three vintage vox ac30 repairs that came to me over a few weeks in summer 2015. Vintage amps have a particular smell and when there are 3 vintage vox amps in the workshop for repair you soon become very used to it!

This amp is probably the toughest repair job that I’ve worked on over the last 6 years. Another repair company in Lincolnshire, experienced with vintage amp repairs, had looked at the amp but had ultimately had to give up. I don’t really blame them.

This vintage Vox AC30 (there’s a picture of it on the 1961 vox page too) is I think a 1970s model. I’ve estimated it at 1973, with substantial modifications through the years. However, I’m an electronics geek, not an amp history geek, so I may be wrong. Someone who’s opened up the amp in the past has written “1978 ish ? 1986 as well, mostly ?” inside it. I judge it to be 1973 because the vox logo is a traditional VOX logo as used in the 60’s, but this could have been swapped during it’s lifetime. Early 1970s vintage Vox AC30s used PCBs too. STragely, this doesn’t look like any of the 70’s PCBs that I could find. So, the jury’s out on this one!

Some 70s vintage Vox AC30s came with reverb circuits, but this amp uses a solid state reverb circuit that I can’t find any record of in 70s amps. You can tell that the amp didn’t ever have a valve reverb because it’s a 10 valve unit. The ’78 reverb unit used 11 valves with the extra triode used to buffer the signal into the spring reverb and to make up gain after it. But the amp had a reverb market on the front panel, I assume this must have been fitted later. Vintage-vox-AC30-repair

I’ve spoken before of the peculiarities of doing amp repairs on guitar amps and other electronics is that the actual process of repairing can take just 5 minutes, but the fault replication and diagnostic period is often much much longer. This problem is made worse in situations when the problem disappears intermittently. This one would disappear as the amp warmed up, after 20min or so.

The fault turned out to be a loose turret connection between the normal preamp volume control and the phase inverter. The connection appeared to be physically intact with a good solder joint. Grounding the point through the pot appeared to have no effect. However when removing this turret it broke in two. There must have been solder holding the piece together, but not making a reliable connection.

After that was fixed, we decided to wire out the solid state reverb unit and return the unit to vintage AC30 spec by adding back in the LoGain input on the vintage channel. While doing this I noticed that someone who’d worked on the amp, probably whoever fitted the reverb had wired up the input jack wrongly, leaving the brilliant channel jack socket with a high resistance to ground at all times. This turned the unit into a pickup point and the amp was feeding back on its own at high treble settings, with no guitar plugged in. Nightmare! Anyway this was soon fixed.

When finished, this is easily one of the nicest sounding amps I’ve ever played. I love the way the Vintage Vox AC30 circuit distorts. It’s easy to see why it’s become a popular circuit for the likes of Dr Z, Trainwreck, Matchless, Bruno etc. to copy. You can see a bit of it in the quick video I did to celebrate it’s finish!

This vintage vox AC30 repair took a good deal of effort, and I was the second repairer to work on it, bit I’m glad to say that it is now fixed. If b you have a vintage vox AC30 and it’s in need of a bit of TLC, please so contact me via the contact page.

Vintage Vox repair – 1961 AC30 repair

Vintage Vox Repair

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.

This is (as far as I can tell) a 1961 model. 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.(!)

After laying down his axe many years ago, the customer decided to sell the amp and brought it to me to service.

I found that the brilliant channel didn’t work. This turned out to be an out of tolerance resistor in the gain stage and a faulty coupling capacitor. Also the tremelo system wasn’t working. In vintage vox circuits, this consists of 6 triodes worth of analog electronics. 2 are an audio input buffer, 2 create a modulating signal and 2 mix the modulation with the audio signal. The fault was with the modulation circuitry and was again down to a worn out capacitor. This is not an uncommon task in vintage Vox repairs.

As 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.

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.

Vintage AC30 repair – 1962 Vox repair

1962 Vintage Ac30 Repair

The guys over at Confetti in Nottingham brought me this vintage AC30 repair. It appears to be a 1962 JMI era Vox model but I’m an amp tech, not an amp historian, so I may be mistaken! It’s definitely an AC30/6 model, only made in smooth black vinyl in 1962. It’s very nice!

The customer brought this to me because they were worried about the amplifier getting very hot. I also noticed that the power cord was damaged and that the amp had a ‘Pin’ style voltage selector common in vintage amp repairs. I always recommend that this is wired out if not already.

The power cord has been replaced and the voltage selector wired to 245 (best match for modern UK), so the switch is now a dummy.

The overheating was caused by leaking reservoir caps which were replaced. Electrolytic caps have a lifetime of about 20 years so leaking caps are common in vintage amps. Faulty capacitors can lead to a much higher current draw through the transformer, overheating it, causing the issues we’re seeing. It also ties in with the internal HT being over 100V too low.
Vintage Ac30 Mains transformer temperature rise
I noticed that the tremelo mode switch had come loose and the resistor wires have sheared at the body of the device. They were replaced using vintage style carbon composition resistors for authenticity’s sake. (Do carbon composition resistors make a difference to tone? According to R.G Keen, The jury is still out!). If you have one of these vintage units, make sure that you keep the switch tight to avoid similar problems.

The amp didn’t run especially hot after the caps had been replaced. The output valves are all matched and measure sensibly, and the amp is cathode biased, so there’s little risk of the output stage being out of spec. I had another vintage AC30 repair in (a cream ’61 model), so I was able to make a proper comparison of the running temperature of the two amps. You can see how close they were in the graph above.

I’m pleased to say that the customer was very happy with the vintage AC30 repair! If you have a Vintage vox, or any guitar amp in need of repair, please get in touch.

Vox Repair – AC30CC2

Vox Repair, AC30 Repair

Much as its nice to be taxed by a complicated repair, I love a simple job too! Despite a number of problems, this Vox repair was an easy fix for the customer, in fact, thanks to a dodgy screw the hardest part was getting into it! The customer complained of a crackle and intermittent volume dropout – I was able to sort both problems out for just £30!

These amps with the Alnico Blue speakers do sound great. I’d recommend checking them out.

If you have a Vox repair that needs some attention, please get in touch.