Gibson Mercury II ......... bit of a challenge !
1) Just a word of caution.
I haven't been able to contact all of the people mentioned below to verify details, so apologies if there are any mistakes. If anyone mentioned would prefer not to be included I'll be more than happy to edit them out.
You'd have to be ever so slightly mad to take on a project in this
state, but this one's a bit special. I got it from Buzz Elliott up in
Cumbria. He sold it on behalf of a friend who had owned it since 1975.
You can see Buzz on stage with The Bullfrogs in 1995 at
and in 2010 with Slagbank at
This is the gist of what he said about the Mercury.
the mid 1970s the other guitarist in my school band 'Eight Hertz'
aquired the amp from another local band called 'Rue & The Rockets'.
They had bought it from Jimmy Henshaw who played with Carlisle 1960s
band 'The VIPs'. We used it for about five years, after which my friend
stopped playing regularly, and the amp was put in storage.
Unfortunately, over the past 25 years it has deteriorated into quite
poor condition due to being kept in various unsuitable places such as
attics, outbuildings and garden sheds etc.....
speakers in the cab are the same ones that were in when it was bought
by my friend, but we do not know if they are the originals. They are
still working and sound loud and clear. The speakers are Celestion G15C
50W 55Hz bass resonance.....
Buzz has very kindly looked into the amp's history a bit more.
Hello again Chris, I have been trying to do a little research regarding the Gibson Mercury and I can confirm the following:-
Steve Wilson (Eight Hertz) owned it from 1975/6 until you purchased it.
originally thought that Steve got it directly from 'Rue & the
Rockets', but he tells me that he actually got it from a family band
called 'The Macauleys', who appeared on the UK Television show 'New
Faces' round about 1974/5, I've tried to find out info' on the net about
the 'Macauleys' on this programme, but to no avail.
The rest of
the story is pretty much as I told you:- that they purchased it from
'Rue & the Rockets' who used to use one either side of the stage,
(we used to call them the Gibson pyramids), and they got it from Jimmy
Henshaw, I'm not quite sure of the dates that the amp changed
Now I've tried to track down The Macauleys too and, although there are New Faces contestant lists, they're incomplete.
Have a look at Alastair Duncan and John Fisher's web site
site has been growing for ten years now and it has a huge amount of
detail about 60s and 70s bands based in and around Cumbria, charting
their influence on the British music scene.
If you go to the section about Jimmy Henshaw of The VIPs, there's a description of a
VIPs' gig at the Scotch Of St James club in London on 26th September
1966. (Thanks to Alastair and John for permission to use it).
the interval arrived, Henshaw was approached by another good friend,
Chas Chandler (of the Animals). Chas grabbed Henshaw’s arm, keeping his
voice low. “I’ve got a guy with me who wishes to jam with your band”.
Jimmy quickly replied “That’s OK, he can plug into my lead amp”. Henshaw
knew how to build amplifiers AND how to produce a bigger output than
the manufacturer’s recommendations – however, he was concerned when this
strange but polite and friendly guitarist began to wind up the volume
and tone controls. “My name is Jimi Hendrix. Could we start with
‘Summertime Blues’ then see how things go?”......
years later in 2006 the Cumbrian based 'News & Star' published an
article with a photograph of Eight Hertz on stage and a follow up.
an observant musician like Jimmy Henshaw would notice in last week's
picture of group Eight Hertz that one of the guys was using his old amp.
"It's the one I used when I played with The VIPs during the sixties and
the one that Jimi Hendrix plugged into on his UK debut," remembers
Jim died in 2007 after a long career in the music business. All the
more reason then to get his old amp up and running and to keep as much
of the existing wiring and components as possible. Not that easy
unfortunately given it's present condition. If anybody has more
information or memories please get in touch.
The VIPs' music is still very much available. Amazon have a compilation CD, with 28 tracks of studio and live recordings.
Audio CD (November 27, 2006) The Complete V.I.P.s [Import][Original recording remastered] Label: Repertoire ASIN: B000K2RD3K
Thanks also to 'juckreizdelmenhorst' for the YouTube post at http://youtu.be/yoTAdGFqoh8. Walter Johnstone would probably have been the drummer on this recording, not Mike Kellie.
23rd March 2010
to everyone who got in touch and a special thankyou to Brian Atkinson
who sent the following email. The references to the electronics won't
make much sense until you read the rest of the page, written some time
my name is Brian Atkinson From Carlisle. during the late sixties /
early seventies i was employed by JP Dias Ltd music dealer in carlisle
and remember the gibson mercury amp you are repairing, i repaired it
many times after Jim Henshaw had parted with it.I can confirm that Jim
did the mods to it. The transformers are indeed selmer although at first
the gibson mains trans powered it till a big burnout in the output
stage took the transformer as well due to someone trying the old silver
paper round the fuses trick.The amp probably had been run without a
speaker cab connected as the octal bases had "tracked" between heater
and anode pins 2and3.The re build included new mains trans mc murdo
octal bases screen feed and grid stopper resistors but can't remember if
i fitted the caps they sound like the 32 mF 500 volt 500 mA caps that
were used in the selmer tv100 type amps.I haven't seen this amp or it's
duplicate which belonged to frank kenyon for years although i am still
in touch with one of the "sister" amps previous owners. As for the
speaker cab i would be shocked to discover Jim had fitted the 15"
celestion spider frame speakers which probably came from a vox T100
cab(2x15") or from 2x vox T60 cabs which had a 15 and a 12 in them.As i
recall the knobs were all black apart from the power switch that was
red.Don't recall any problems with that type of power switch but i liked
the idea of it.The 10" driver from the cab was a sealed driver for high
frequency use and there was a crossover in the cab which i may still
have !! For some reason i think the cab had 4 x 10" celestion drivers
that marshall used but maybe that was the "sister" amp.Hope i have been
some use and feel i should mention Jim was very much a local music and
Electronics Hero looked up to by all the local musical beginers like
myself and by established players Sadly missed !! R.I.P jimmy! Regards
As Brian points out, Frank Kenyon also used a Mercury setup. I wonder where that is now.
14th October 2010
thank-you to Brian and Keith Jefferson for coming up with this
photograph of The VIPs on stage at the Star Club in Hamburg. Jim is
seated at the keyboards on the right with his Mercury in the backline.
Frank Kenyon is standing in front of his matching set-up.
Greg Ridley is on bass on the left, Mike Harrison is on vocals and Walter Johnstone on drums.
2) So....What to do with it ????
is going to get complicated now because it isn't actually a standard
Mercury inside the box. Over the years the power section has been
rebuilt as a typical 1970s 4xEL34, 100watt job. Output valve bases
(including two extra ones), electrolytics, mains and output transformers
are new. The choke is original Gibson.
When was it first modified ? I don't know but it was probably after the Hendrix session.
pot source/date codes indicate early 1964 so the original amp must have
been made after this and I can't see anybody, especially a working
musician, stripping a very expensive, one/two year old import.
the replacement caps is marked with the rectangular RS logo (instead of
the Radiospares flying man) and I don't think this appeared until 1971.
The speakers are a bit of a puzzle. According to the Celestion web site, their date codes (26LG and 29LG)
could indicate the 26th and 29th of December 1962 or the 26th and 29th
of November 1997. Since December 26th was a Bank Holiday (Boxing Day)
and the factory at Ipswich apparently didn't open until 1968, that would
make them 1997.
state that the other LG possibility (November 1974) would have the day
code after the letters, e.g. LG26. Informed opinion though suggests that
the date code list is over-simplified and that some speakers from this
period were actually stamped day-month-year. That and the fading of the
cone material (plus the amp's history) make November 1974 the most
asked Celestion (very fast and helpfull reply by the way) who agreed
that although mixed up codes from that era were rare they weren't
impossible. We'll never know unless whoever fitted them gets in touch.
electrolytic supplying the preamp is marked P 74 02 (Feb 1974?) and the
two larger Erie caps are AYN KB 706 (June 1967?). The Eries look fairly
worn and, with clamp marks at both ends, they were probably second hand
when they were fitted.
The whole chassis has been sprayed with grey primer at some time,
probably to stop the rust. Nice to know somebody cared. Bugger to get
When it was new the speaker cabinet would have had one 15" and one 10"
CTS/Jensen driver with a crossover. The normal output power of a Mercury
was 35W so the originals obviously had to go when the amp was modded.
Replacements are Celestion G15C 15" rated at 50W each (see update in section 1)
Part of the tuning port has been cut away next to the old 10" position and the hole in the baffle has been almost blanked off.
wouldn't be too difficult to put the speakers back to normal but there
wouldn't be any point. The originals wouldn't handle the power anyway
and it would destroy forty five years worth of history. (Have a look
at section 16 to see what happened next)
The back of the cabinet is in two parts with a tilt-back leg recessed into a centre strut.
don't know when the rig was last used, but the whole thing is too far
gone to just switch it on. Apart from dire state of the mains wiring one
of the screen grid resistors has been running hot and burnt off the
printing. Right next to it is a hole melted through the heater
wiring. It's possibly an old short that's been pulled apart.
Unfortunately, history or not, a fair amount of wiring will have to be replaced before it's safe to use.
The most worrying things is the mains on/off switch. See section 9 below.
existing switch is rated at 3A at 110V A.C. or 1A at 250V, although
250V operation wasn't an option on the original amp. A new switch would
be favourite given the state of it. The original fuse holder has been
changed to a 20mm version mounted in a grommet (presumably to clear the
new mains transformer) but the original Leecraft 125v neons are still
6) Gibson Mercury Schematic
This is what survives of the original circuitry. The shaded area is Gibson. The rest of the components are modifications.
This is what the original would have looked like.
7) Clean Up
front panel was a lot worse than it looked in the 'before' pictures at
the top of the page. Most of the plating was sitting on top of rust and
it was just falling off. It's surprising how much of the screen printing
survived. Shame it got into this state but, hopefully, it won't get any
big problem is trying to find some replacements for the missing
control knobs. They were made by Rogan (who also made knobs for cooker).
They measure 28.5mm across the circular part and fit split, 1/4", 24
spline shafts. There are seven missing altogether including the red one
that fits the power switch.
8) Output valves
Got the AVO valve tester out today.
four EL34s came out some time ago so I'm not sure which one went where
but, judging by the damage to the base, valve d was in the socket where
the screen grid resistor shorted out.
The AVO test results should be: Ia = 75mA, mutual conductance = 11mA/V
Test settings were: VA = 250V, VS = 250V, VG = -13.5V
|Valve ||Manufacturer ||Date Code ||Isolation (hot)|
Cathode to Heater
|IA ||Gm |
The cathode to heater leakage in valve c doesn't really matter in this circuit as there's very little potential between them.
9) Power Switch
worlds most complicated on/off switch, made by CTS. The source code
stamped into the metalwork indicates a manufacturing date of Septmber
1963. This ties in nicely with the early 1964 pot codes.
Gibson used a four way switch designed to work with the USA mains system. The Mercury handbook explains it's operation.
convenient switch has been provided for performing a total of three
functions, turning the amplifier on and off, putting the amplifier in
'Standby' and selecting the proper polarity of the power source which
reduces the A.C. hum and other extraneous noises to a minimum. In the
'Standby' position the amplifier is kept 'warmed up' and ready to play
at the instant the switch is advanced to the 'On' positions. Two 'On'
positions have been provided. The hum and hiss levels on one of the 'On'
positions will be noticeably lower - this is the correct 'Polarity' for
using the amplifier.....
locations of extremely high noise levels, clipping the 'Ground Clip' to
a grounded object will greatly reduce objectionable noise and hum....."
the switch does in practice is couple one or other of the incoming
power wires to the chassis via a capacitor. The user selects the switch
position which gives the least hum and noise. This feature isn't needed
with the UK mains system.
mains power is controlled by a single pole, single throw unit at the
back of the assembly (the third contact seen in the photo isn't
connected to anything inside the switch).
Removing the rear section reveals a steel plate and a pressed-on actuator.
the steel plate is a three pole, four way, ceramic wafer switch which
takes care of the HT switching and mains polarity selection. The moving
contacts are held between two rotating plastic mouldings which are
welded together. Apart from pulling the wafer off the spindle, this is
as far as dismantling can go.
Now that the power switch is clean and I've had a look inside, I'll have a go at re-using it.
Below is a representation of what goes on inside the switch.
10) Mains Wiring
know I was going to leave as much as possible alone but, since the
mains wiring is so badly corroded, it's got to be replaced. The paxolin
sheet holding the transformer voltage selector is broken, it's missing
the selector link and it's been hard-wired to 245V. Since the
transformer is bigger than normal, the selector link would be vulnerable
sticking out of the cabinet so the mod isn't a bad idea. I've put it
back to normal for the time being just to test the other voltage taps.
The transformer itself comes from an old Selmer amp. (see update in section 1)
11) Indicator Lamps
neon indicators are the original Leecraft 'Snaplite's rated at 125V,
1/3watt. Both were suffering from brittle insulation on the connecting
leads and one lead actually fell off when it was moved. The orange lamp
also had an open circuit resistor.
The only way in is to cut around the body at the lead end.
One new 47k resistor later, plus some new wires, and they'e all Araldited together again.
existing neons can be run from the 125V mains tap using the TX primary
as an autotransformer. Just got to figure out the best way to rewire it
been having a look at the 32uF cans to see if they can be rescued.
They're lovely old Eries rated at 500V and 500mA ripple and I just can't
bring myself to change them for some skinny modern things. They both
read OK for value on a bridge and I've had a quick go at re-forming
them. So far it's going well although I need to rig up a higher supply
Both cans have dents that don't match the clamps so say must have been round the block a bit before. (see update in section 1)
13) More rust
top of the chassis was so badly corroded that I've given up and painted
it. The rust has been ground off and the bare metal primed with zinc
based, cold galvanising paint. On top of that there are two coats of
grey primer and a gloss coat. The transformers were removed and painted
separately but the top mounted valve bases were just masked off to avoid
disturbing the wiring. Boyd Coddington might not have been impressed
but it hasn't turned out too badly and now everything can go back
together. It would have been a lot easier to strip the whole thing back
to bare metal and powder coat it but that would have meant stripping out
all the vintage wiring and that wasn't the idea.
14) Switch On
an earth continuity and high voltage insulation test, the amp (minus
valves) was powered up gradually with a Variac over several hours to
give the capacitors a chance to reform. It's worth remembering that the
DC voltages will be higher than normal if the valves aren't in and
The good news:- The power switch worked and the HT started coming up.
bad news:- Turning off the power to go and make the tea produced a loud
clunk and instant darkness as the mains RCCB tripped out.
culprit was that d****d power switch again. It was fine moving
clockwise but wear in the detent mechanism was allowing the internal
contacts to short out when moving back to the off position. The result
was a short between the HT section and mains neutral (sections C and D
in the switch diagram above).
(Long pause for jumping up and down and swearing a lot)
was going to scrap the switch but, after a day to think about it, I
stripped it down and managed to repair it. It now copes with a 750V DC
isolation test with no problems.
The separate 125V
feed to the indicator lamps works well and the switch operation looks
original, Off - Standby - On - On. Finally the amp is producing 100W rms
into a dummy load.
15) It Works!
didn't have any way of measuring the bias current directly (no cathode
resistors) so I set the bias voltage to -34v as shown for the Selmer
PA100. Turning out the lights and just getting rid of the red-plating
gave a final setting of -36v.
it into a Marshall 2x12, stood well back and switched on. Success. No
loud bangs or smoke and all the pots were fairly quiet. Plugged in the
workshop Dano U2 (wanted something cheap to drop if I had to run) and
turned everything up to halfway.
thing is loud and definitely vintage. No extreme top end, but a good
thick sound (not easy with a U2). I've only played through it for ten
minutes or so but it seems to be cleaning up slightly so I guess it's
burning off ten years of damp and decay.
were two main problems. The first was a very loud background hum,
eventually completely cured by re-fitting the two screening plates
around the pots. The second was mechanical noise from a couple of
microphonic EL34s. This can only be cured by replacement and that will
have to wait.
The chassis is held in the cabinet
by four 'spire' or 'U' nuts. The originals are long gone, so these are
M5 replacements obtained from ADI Components in Derbyshire.
potentially dangerous area is the metal mesh covering the bottom
cut-out of the cabinet.This can get bent backwards when the chassis is
pulled out and stick up into the electronics.
Be sure to cut off any wire that can't be flattened out and secured.
16) Cabinet Tragedy
Thought it was time to have a closer look at the cabinet. Big mistake!
must be the most unlucky cabinet in the world. What looked like part of
Hunstanton beach falling out of the bottom was actually the remains of
the plywood after the woodworm left. They probably left when the floods
arrived to saturate the bottom four inches of their home. Oh well. Put
the kettle on.
17) OK. So it's next year and the Sun's out again. Time to get back to it.
First step was to cut away all the rotten ply in the side panels.