CHAMP ELECTRONICS -" THE VALVE AMP HOSPITAL"
SERVICING A JMI VOX AC4 COMBO
This had had some strange modifications done. The on/off switch had been disconnected and used as a standby switch instead! The mains power came straight on when plugged in!
The speaker is one that the owner (Graham) had sourced for it, as the original was missing. He told me he got this from the USA. It is actually an Elac with a cover over the Alnico magnet. I have never seen one like this before, or in this colour. Maybe it was an export version for the US? However, it was also 8 ohm and we needed a 3 or 4 ohm for the job.
Here I have fitted a fly-lead with an in-line phono (RCA)
socket, for the tremolo foot-switch. I also told Graham that I could straighten the dented front panel but we could lose some of the paint in doing so! The paintwork on these is pretty much just a waft-over…with no undercoat/primer and
it flakes off very easily. Talking about the paintwork…….Salmon-Pink Hammerite? !!
The Chassis front panel has been straightened here, with a small loss of paint as predicted.
All finished here and with just a few new components; along with a new power switch/tone control. Note the novel idea of fitting a jack socket directly onto the output transformer…..so other drivers could be tried. This was a request from Graham. Also, the blue multi-turn pre-set pot. This is an addition by myself
which gives the owner the ability to change the depth of the tremolo which, on these, is fixed and not always everybody's cup-of-tea! Lastly, note the large washers
that I have used at the top of the panel for mounting. This makes things a lot more secure.
And finally all back in the case. Here I have fitted an 8" 3 ohm driver (God knows what brand it is?), but it's perfect for the job. I also do a small mod on these which really brightens them up a lot….they are usually a bit muddy sounding!
Cute little thing.
Here is Graham's testimonial mail:
"Hi John. The amp is now a delight - it now has surprising clarity and sparkle with hardly a hint of its earlier muddiness - whatever you did with that tiny mod has improved it no end - not so much a treble thing but more of what would be termed the "Presence" or
"Brightness" of a bigger amp!
I have spent hours with it today and it really has become a nice little thing - a very tactile and responsive feel; quite the opposite of what you normally get from these things - very pleasantly surprised!!
Also the trem set-up - normally the trem on these smaller British (and American) amps is relatively unusable or at best something you would only find a use for occasionally but by getting that
little trim pot installed it has all changed - with some reverb added into the mix it now has what is practically a "chorus" sound as opposed to what I would normally think of as a tremolo - very nice indeed and now a very usable effect - I am very pleased!!