CHAMP ELECTRONICS -" THE VALVE AMP HOSPITAL"

NOTTINGHAM, ENGLAND

 

REPAIR OF TWO JACKSON MODEL JG3 100 Watt GUITAR AMPLIFIERS

 

 

 

 

 

 

After a fairly long drive down from Leeds, England on an unusually hot Thursday, a gentleman called Dave brought not only one but two identical Jackson/Charvel JG3 amplifiers. I was well aware that Jackson/Charvel made guitars, and I had a vague recollection of them producing guitar amplifiers at some time, but this is the first time I have actually worked on them. On the information plate it states:- "Jackson/Charvel, Fort-Worth, Texas" and then “Made in England!” One can only assume that they were American designed and then assembled in the UK.

The amplifiers themselves are not bad really. They are very well made; very strong and sturdy. The pre-amp sections unfortunately are on a printed circuit board, but what the heck, this is quite the norm nowadays.

The first one was completely dead, as Dave had already stated on the phone. The pilot lamp and tubes lit-up, but that was it! On removing the amp from the case, the first obvious thing that caught my eye was the lack of any connections on the standby switch! It appeared that after completion, when the cable-ties were put onto the wiring looms, the two spade-connecters on the standby switch had been almost pulled-off. Then over time, they had just simply “come off”, hence no amp! Cutting the over-tight ties and replacing the spade connectors saw the amp come to life. She was still not doing the business though, but a couple of new EL34’s, a few other components, and away she went……cool!

OK, then onto Amp No 2. This one was actually working, but apparently it just kept diving in power and volume. And yes, this it did do on the test gear in front of my very eyes. Time to remove this one from the case too.

At this point I will say again that when any of my customers travel a fair distance for my services, I try to do the job(s) whilst they are here in the workshop. This saves them time, money in the form of fuel, and the effort in having to come back to collect their beloved babies. However for once, after reviving amp number one and now on amp number two, more than five hours had passed! Whilst Dave wasn’t pressed for time, I was getting a little fatigued and needed to take a break! The problem with Amp No2 was that the two front end input circuits were fine, the back-end phase splitter and output sections (after a juggle of the EL34’s) were also fine, but the bit in the middle, i.e. the tone circuit, had a fault somewhere. This fault was causing the waveform to distort immensely, and also the drive was being crippled by this too.

For 99.9% of the time I don’t need a schematic when working on amplifiers. Following a circuit is like being on “auto-pilot” for me, but where this falls down is two-fold: 

1. When you are not familiar with an amp and, 

2. When there is a circuit board and you cannot see on the other side what is going to where. 

These were the problems that I was encountering with this particular amp. As there was no schematic available, I had to remove all the front control potentiometers in-order to get the whole circuit board out for “fault tracing”. I had suggested to Dave that this one was going to be a bit of a *******, and that I would need more time. I asked if he would mind leaving the amp for collection at a later date? This he agreed to do with no problem and consequently left for his journey back home in Leeds.

After about a half hour break, a couple of cups of tea, and a couple of fags (sorry cigarettes!), I decided to get my head back around the circuit. The tone circuit on these amps is like “sort-of” five band; there are bass, treble, middle, presence and a three position mid-boost/sweep switch too. This being the case, there are of course quite a few components around these tone circuits, and I knew that the problem was around that area somewhere. After a further fifteen minutes or so on her, after my break and as we say here in the UK it was “sods-law” that I found the problem. This would have likely been before Dave had even arrived back at home in Leeds. One simple, small, .01 capacitor was OC (open circuit)! A bit unusual but nevertheless there it was. After changing this the whole thing burst back to reality. Exactly the same power and performance of No1. Phew at last!

I soak-tested both amplifiers for a further two days to be sure all was OK, before letting Dave know they were ready for collection. Once again, another job done well..........and another satisfied customer.

Thanks for looking, John.

 

 

 

 

 

 

 

 

 

 

 

 


 

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