Carol-Ann British Series 67-18C 18 Watt Plexi Combo
The Carol-Ann British Series 18 Watt Plexi Combo is here!
A while back we went to Alan Phillips to see if he would be interested in us commissioning him to build two different Marshall style amplifiers for us. We were looking for an 18 Watt Plexi head, and a tube rectified JTM50 head. Being extremely well versed in vintage Marshall amps, Alan loved the idea of the JTM50 (he owns a great sounding one) but he wasn't so keen on the 18 watt head. First of all, there were never any 18 Watt Plexi heads, just combos. But even those were very hit and miss. He said some sounded great, but others very bad. If he were to do this for us, he wanted to make absolute sure they sounded phenomenal.
Alan said he had a friend with the best sounding 18 Watt Plexi combo he'd ever heard. He was generous enough to lend it to Alan in order for him to replicate it tonally. Bear in mind, this is no easy feat. Components have changed a good bit over the years and copying a schematic part for part WILL NOT give you the same results as they did in 1967. Alan had to do a good bit of tweaking to the circuit to get it to sound right.
We had originally suggested the Tremolo circuit be omitted from this amp altogether, but Alan insisted the Trem is a crucial part of what makes this amp sound the way it does. The Tremolo circuit has historically been a bit difficult for amp builders to tame (which is one reason you rarely see highly reputable amp builders offering this) but Alan made the proper adjustments in order for it to be stable and reliable.
Power: 18 Watts
Power Tubes: 2 x EL84
Preamp Tubes: 3 x 12AX7
Rectifier: EZ81 (New NOS from Late 60's)
Controls: Channel 1: Speed, Intensity, Tone, Volume, Channel 2: Tone, Volume
Switches: On/Off , Standby/On
Grille Cloth: EC Collins Bluesbreaker Grille (read about this below)
Speaker: Celestion Creamback G12M (standard) or optional G12M Heritage
Initial Production Limited to Only 5 of these!
About the EC Collins Grille Cloth used on this amp:
Okay... We know what you're thinking. We thought the same thing when Alan insisted we use the EC Collins Grille cloth, despite the expense. Believe it or not, this grill cloth accounts for about $300 in the 67-18C's cost. This stuff is pricey! Why? Well, it's very hard to manufacture accurately. The knockoffs out there, while they look fine, DO NOT replicate the tonal changes the fabric makes.
Paraphrased from the EC Collin's Website: The EC Collins Bluesbreaker grill's surface is covered by wide, heavy and dense rubberized stripes which are divided only by narrow areas of venting, making it *not* acoustically transparent. Grill cloths typically strive for total transparency, but this creates a unique equalization filter that changes the tone. When stretched, this considerable and "weighty" displacement lightly impedes airflow and dampens the free movement of the speaker's cone. Most importantly, the cone delivers 100% of the sound with air the transmitting medium, but the cone also weighs mere grams and is by far the lightest, most acoustically sensitive component in the entire amplifier. It really doesn't take much to generally manipulate its performance (as chemically removing the edge doping or using a closed vs. open back cabinet can demonstrate), but it does take quite a lot to precisely improve a speaker cone's tone in an authentic JTM kind of way.
You can read much more on the EC Collins website HERE. Their website is a bit gaudy and seems over the top, but Alan at Carol-Ann (who is known for NOT being full of mojo snake oil BS) says it's actually very valid. Play this amp through a standard grill, then through an EC Collins, and the difference is very apparent.
About the speaker we chose for this amp:
So, several speakers were tested with this circuit through the EC Collins grille. We thought first about going with the Celestion Heritage G12M Greenback for a number of reasons. It's different from the standard Greenback in that it's a dead-on replica of the 20 watt pre Rola T1221 Greenback from the sixties. The standard Greenback has evolved over the last 50 years and doesn't sound like the original. We were pleased enough with this, but when we tested it with a Celestion Creamback G12M, it just sounded better. No two ways about it... The Creamback G12M is a very popular speaker these days, and we didn't want to come across as cliche, but at the end of the day, it was indeed the best choice. With that said, if you are interested in this amp and would like the Heritage G12M 20W, we can still accommodate. Just let us know.
More History of the Carol-Ann British Series (from the Carol-Ann Newsletter):
Recently, Humbucker Music approached me and asked if I was interested building a couple of models that were tonally authentic to some of my favorite amps from back home in England. Given the wide array of awesome British amps from the late 60's, I thought it would be a lot of fun and a change of pace and so chose my own two favorites to base the models off. A '67 JTM50 head with EL34's and GZ34 rectifier and a '67 18W combo with Tremolo.
Despite the following and the number of clones out there doing one of these amps 'properly' was a little different, I had serviced and played many over the years back home in England and I certainly remember there were good ones and some not so good ones. After a couple of calls to friends in the business I managed to borrow a 'very special' original '67 18W. I was taken aback how great this amp sounded and found myself lost in it just playing for about an hour. Lovely amount of gain, very thick and harmonically rich, not at all bright and harsh and incredibly tight but bouncy in the low end, even when on full volume. I'll be honest, this was the best 18W I've ever heard. Heres a room clip of that amp: https://www.youtube.com/watch?v=TnVbekHxZL0
The goal of this project was to aim for the tones of both these amps, not a 'component for component visual' clone. There's also 48 years of improvements on electrical safety and a much much wider selection of components theses days so to restrict oneself in such a way would be a backwards step.
Once I had taken the measurements to determine the basic operating points, the amps were pretty much closed up. It's important to let your ears do the listening , not your eyes when you are trying to replicate tones. If you focus too much on the exact values you will end up straying off the tonal path. Tonally replicating a specific amp is way more than just cloning the sum of its parts. That said there were a number of 'stock' component value differences in the 18W to the schematics you find for this model. One of the differences was actually very important and explained why this particular amp sounded so good.....but that little gem stays with me :)
One thing that did become obvious when trying the 18W with different speakers and cabs was that the actually grille cloth used on these combos, the original 'Pinstripe', had a massive bearing on the tone, in a very positive and pleasing way. However, finding that grille cloth was no mean feat. After much searching I found one person on the entire planet that made this cloth and he had gone to the absolute extremes of detail replicating it. The Gentleman's name is Eric Collins (http://bluesbreaker-pinstripe.com) Anyone that knows me, knows that I'm an Engineer and a Guitar Player, I don't live in a world of 'Mojo' and 'Snake Oil'. Thankfully for Eric I had done my own testing and knew there was nothing I could do with the circuit to replicate the frequency specific reflections and attenuation this grille cloth has and it is so critical. Over $300 for a piece of grille cloth for a single one 1x12 may seem a lot of money and it is......but this isn't any grille cloth, its a critical component of the amplifier. Additionally the period correct look is awesome and a very rare sight on any modern amplifier.
With regards to other interesting component ventures. I tried no less than eight different coupling capacitor, types including some of the ones that are sold as specific replicas of the original Philips Mustard Capacitors used in these amps. While all of these Polyester Metal Film Capacitors sounded great, I found one less commonly used type made by CDE that to me nailed the Mustard tone better than the others.
I even went to the extremes of ordering the correct gauge wire and colors from RS Components in the UK...including the infamous 'Pink' wire that is impossible to buy in the US. Getting this wire in my shop was like being reunited with an old friend.
Tube selection took a similar venture to capacitor selection. I found modern ones that best represented the Mullard originals. The only tube I ended up going NOS was the EZ81 rectifier tube for the 18W. I didn't like any of the new production versions of this tube. As with the rest of this project, if it truly needed to be NOS, then it would be.
The cabinets use period correct tolex and fittings and are the exact dimensions of the original.
I did make improvements to the 18W tremolo circuit and the grounding schemes of both models for a lower noise floor than the originals.
All in all this was a fun diversion from my normal amps and I found myself working on this project in leisure time as well as work time. I'm very happy with the final product and I feel anyone who is very familiar with these model would agree I have managed to replicate the tones of these specific great examples of these classic amps with the benefits of lower noise levels and reliability.