CHAMP ELECTRONICS -" THE VALVE AMP
HOSPITAL"
NOTTINGHAM, ENGLAND
SERVICING OF AN ECHOLETTE M120 PA
AMPLIFIER
Sent to me by Oliver, from
France. This Echolette M120 PA head "just wasn’t doing the
business"….as explained by Oliver.
Rear view - This had been worked
on a few times before and some really strange modifications had been
done. Note the two output impedance choices…..5 and 20 ohms,
a little out of the ordinary!
The top four tone controls (one
per each channel) were of the pre-set type potentiometer with a
“screwdriver slotted type of knob” to adjust them.
All four of these potentiometers were pretty much duff and, as this
type/size/style are no longer available, I needed to replace these 2M2
pots with a modern bolt on type together with a new suitable knob. In
this photo you can in-fact see just one of these replaced with a new
retro style knob. I also changed the main three master controls with
the same matching type of knobs, but larger ones which really looked
good. At this point I sent this photo to Oliver to see if he was happy
with the style of knobs I had chosen to use? He was so…..I
continued with the job.
On this photo (as received) you can see
how the previously replaced main smoothing caps were just hanging on
wires and falling around inside the chassis! All the pre-amp tubes are
ECC808’s and the pair of output tubes are EL503’s.
In-fact, Oliver originally sent me this amp, not only for a good
service, but also with a view to doing my super conversion from
EL503’s to EL36’s. (Please see this article
http://www.chambonino.com/modify/mod1.html and this article
http://www.chambonino.com/construct/const8.html ). However, as the pair
of EL503’s in his amp was in really good condition and
performing great, I advised Oliver that the conversion wasn’t
really necessary at this point in time.
Some
French engineer had changed the two output tubes’ cathode
“bias-check” resistors for 47 ohm and 56 ohm
respectively…..how stupid! The tubes are in fixed bias with
individual controls……I replaced these two resistors for 1
ohm…..sensible and more accurate! Also, someone has changed all
the heaters to DC. This is usually a good thing but in reality, I
don’t think it would have been such a big issue on this amp! Here
you can see the two large, black bridge rectifiers and the added caps
on the main board for this DC heaters modification purpose.
Although
the changed smoothing caps were fine, they were actually an over-kill
in size and voltage. I replaced them with smaller, more suitable and
practical ones, and fixed them securely too on the main board, with the
good ‘ole faithful “glue-gun”.
The two, more sensible and accurate 1 ohm cathode resistors in place.
The
back of the tone controls. The four new 2M2 pots can be clearly seen
here. Under normal circumstances, I would remove any of the un-used old
hardware but the countersunk heads of the screws from the old
pots’ mountings are under the “glued-on” front panel
(I couldn’t hold the screw heads) and, the nuts had been used
with lock-tight. I didn’t have a
“cat-in-hell’s” chance of removing these, so I simply
had to “break-out” the original pots and leave all the
hardware in place!
Here is
Oliver’s e-mail after receiving his amp back:
"Hi John, the Echolette sounds very good and quite loud
too....I'm happy to report. Thank you for your great work.
Cheers, Oliver"
