This is the super cool JTM45 Offset Marshall I had taken into the studio for some demo clips. Back in the fall of 2006 and throughout 2007, I had acquired a massive collection of JTM45s from a former senior Vice President of Capitol Records, David Kronemeyer.  David had collected these amps over a very long period of time and I was fortunate enough to have been the recipient when he decided to part with his immaculate collection.

I went through each of these amps from top to bottom, combing through every finite detail to be sure they were in good working order, but also to find out all the greatest details I could now finally learn from such a fabulous collection of excellent specimens. Of the 26 pieces that were all top quality JTM45s, 11 of these were “Coffin Logo” Model JTM45 Marshalls. Of the 11 Coffin Logo models, three were of the very first to ever have been built. These are the Offset Coffin logo models. We all have heard of them but few are ever seen in person. Not only are there very few in existence, I had three of the most pristine to be found. Quite a combination on that front. Having gone to a lot of trouble to be sure all the amps were in fine working order, I had taken one of the Offset models and opened it up to give it a good check out.

Notice, there are 6L6 power tubes. As it was, they imported or bought US power tubes since this amp is a dead knock off of the Fender Bassman. The funny thing about it is they used a 3 wire ground plug in the UK in 1964, but the front of the amp has three toggle switches, Power, Stand by and Polarity.  A “polarity” switch was used strictly for 2 wire power systems in the US. The British power system had no need for that polarity switch and later it was quickly done away with. Notice also the storage section on the right. That is where the power cord went. You can also see rivets on the corners. Those were for the support brackets added to the chassis corners since the soft aluminum was not welded down the folded seems. The very first chassis were bought with this upgraded support which they badly needed but after the first batch of amps were built, Marshall decided to fold their own chassis and that did not include the riveted support corners like the first editions. Too bad, that really helped them hold together and not tear.  It turned out that Marshall paid a premium for these first chassis and that is the reason for the cost cutting, make it yourself move.

You might also notice there is only one speaker outlet jack on the back of the amp.  No back panel as these early first editions did not have back panels at that point. The speaker outlets came with either one or two output jacks. One speaker outlet jack meant it was definitely intended as a guitar or bass amplifier. Two speaker outlet jacks were almost always for PA amplifiers. Since the guitar amplifier was sold with a single 4X12 cabinet or in a combo amp later on, they only needed one speaker outlet jack. PA amplifers were used with two speakers and would need two output jacks naturally.  Notice the fuse holder is the Bulgin type like the power socket inlet was as well. That fuse was used on many early vintage British amplifiers. you will see that exact fuse on most all of the early JMI era Vox amps.

You may not be able to see it, but under the speaker jack in the back, there is a resistor soldered across the speaker jack itself. This is a 10K ohm resistor that was used very commonly at the time. I’ve found these same resistors on many early Vox amp speaker output jacks as well. To tell if this were a Bass model or Guitar model amplifier, you can see two capacitors. One capacitor is on the circuit board and it is a large square cap tied across the mixing resistor towards the bottom of the circuit board. This gave the amp a bright channel. Both bass and guitar amps had this capacitor and that capacitor made input #1 a bright channel. The giveaway as to it being a guitar amplifier is the small round capacitor on the volume pot. The brown or redish brown cap tied across the second control potentiometer on the left is the #1 or brilliant channel volume control. This capacitor allowed for brighter sound when used at low or moderate volume levels. When the #1 channel volume was turned up until the the potentiometer wiper would be past the point where the potentiometers resistance was less then the capacitor which was shunting the bright tone across the potentiometer to the amplifier, you would get a smoother sound with a fatter bass but still a focused mid so long as your bass tone control was not turned up far.

We can discuss the interior further when I get to it later. But the good part is next. I took this very same amp into the recording studio for some quick down and dirty demo trax. I wanted to be very simple, yet very honest with the Marshall. I wasn’t afraid to blast it full power and give it the true use I expected anyone would want to use it for. I know it had Radio Spares transformers and those are by far the best built, most durable of all the Marshall Transformers used in the years Marshall built their amplifiers over the decades. At least in my opinion and that of Sergio Hamrick of Mercury Magnetics. I take him at his word. He truly knows his stuff. But back to the good stuff. Not being afraid to open this colectalbe gem up to the full throttle blasting it was going to get, I also hooked the amp to a Mojave 2×12 speaker cabinet loaded with Celestion G12 Alnico Blues. These are newer, not vintage blues. Just for the record, they are the same speaker in every respect sound and quality wise. Using my Baker B1 guitar with a 24.625 inch scale, I had set the amp controls with the following settings:

Presence: 4 Bass: 1 Midrange: 10 Treble: 6 Input channel 1 High sensitivity #1 Volume 10

With those exact settings and with my Baker guitar, bridge pickup around 8.34K ohms, I need only roll the volume up or down to vary from clean to full blown overdrive. The sound clips speak for themselves. I was plugged directly into the amplifier and I had taken the mic’ed signal into the board direct as well. We used an Apple Mac system to record with. The Microphone was an SM57. The sound was sent to the disc and we added some delay on the lead track only. All parts were played by me with the same settings on the amp and the guitar was never changed, only volume control was adjusted for the track I did. The tone control on the guitar was also full up.

Wave file 
http://vintageamps.com/temp/offset.wav 

Mp3 
http://vintageamps.com/temp/offset.mp3 

Like I said, that amp was to die for. Very happy with the dynamics and for one of the first Marshall amps ever built, it delivered in spades. I am very grateful for having that experience in my endeavors of working with vintage amps.

Next month I will show you some other cool model Marhalls from the collection.