"MetroAmp.com is your resource for everything you need for repairing, restoring or modifying your vintage (or not so vintage) Marshall." This is the claim made by George Metropoulos at Metropoulos Amplification. In my case, I was in search of a replica point-to-point circuit board for my Marshall JTM-45 reissue. Did MetroAmp.com deliver? Not only did MetroAmp.com deliver; they gave me the product and information to help complete my quest for a vintage Marshall JTM-45.
Anyone that has heard classic recordings from AC/DC to John Mayall and the Bluesbreakers knows that those classic guitar tones are oozing from a Marshall JTM-45. The John Mayall "Beano" album, Bluesbreakers with Eric Clapton is probably the most famed recorded evidence of the power of this legendary amplifier. Once I established that this was an amplifier I must own, I started my search. Well, it didn’t take long for me to figure out that my tone quest was in serious jeopardy. These vintage amps cost thousands of dollars and, unfortunately, just not in my budget. Where there is a will there is a way and MetroAmp.com has a solution for those that want vintage tones on a budget.
In addition to tubes, amp parts, cases and schematics, MetroAmp.com offers completely hand made recreations of vintage Marshall point-to-point wired circuit boards. George offers pre-soldered Plexi style PTP boards, JTM-45 PTP boards and retrograde kits and also DIY kits of all the above. There is also a chat forum for those interested in all things Metro. All offerings feature 1/8" G-10 board material, carbon composition resistors for their unique tonal characteristics and Mallory high voltage caps for vintage tone. All mounting holes and component placement are exactly as they are on the originals. MetroAmp.com can build these boards to reflect any era of Marshall circuits. From a ’67 Super Lead to a ’69 Super Bass or any combination you desire.
In my case, I acquired a used Marshall JTM-45 reissue in good shape that was well on its way to becoming a vintage JTM-45. The previous owner had already began the process of modifying this reissue’s circuit to vintage JTM-45 specs. The power tubes were changed from the stock 5881 to KT66, the filter capacitors were changed to the vintage values and the amp was re-biased. The only remaining items were to change the output transformer and to pull the factory-installed circuit board and replace it with a PTP board. This is when we contacted George Metropoulos at Metropoulos Amplification to purchase the Metropoulos JTM45 kit.
I placed my order with Metropoulos Amplification and in a flash I received the package. The first thing that struck me about the JTM-45 PTP package was the attention to detail. The kit includes 1/8" G-10 board material, a variety of carbon composition, carbon film, and metal film resistors, and Mallory high voltage capacitors all perfectly soldered and neatly arranged exactly as they are on the original boards. I also received all necessary hook up wire in several different colors and chassis mounting hardware. I also found step by step instructions that are clearly printed and easy to read containing helpful hints and contact information for installation help. Included with the instructions is a color printout of the circuit board on heavy photo paper. On the color printout the components are clearly labeled and color-coded to make for easy installation. There is also an original Marshall amp schematic for those that can read schematics. George offers some helpful hints to aid in the installation and one critical warning about draining the stored voltage in the filter caps BEFORE touching anything inside the amplifier.
When I read that there were potentially lethal voltages stored in the filter capacitors, I got a bit nervous about the project. I have some basic amplifier experience with changing preamp tubes, speakers, etc. I have also changed guitar pots and pickups, but never have been exposed with something as potentially serious as this. I consulted the resident amp expert, David Szabados, and he gave me step-by-step instructions on how to bleed the stored voltages. I remained very cautious throughout the entire modification, at times I felt like the amp might bite me. I feel a little silly, but I guess it’s better to be safe than sorry.
After opening up the amp and safely dealing with the filter caps, the project moved along smoothly. I clipped all of the existing leads from the old circuit board and removed it from the amp. I planned to reuse all the existing leads wherever possible. I installed the new mounting brackets and then warmed up the soldering iron. I followed the written instructions and the color photo and carefully soldered each lead before checking it off and moving on. I came across a few items that threw me, but with some careful consideration I managed to complete all of the connections. As a precaution, I emailed George at [email protected] and asked questions on the items I was not 100% positive about and I promptly received my answers in the morning confirming my connections were indeed correct. At this step, it was time to power up the amp and check the bias, etc.
I consulted with David Szabados and together we switched on the amp and adjusted the bias. For the JTM-45 the idle current should be 40mA. Mine came in at around 35mA. George recommended changing one of the resistors from 47K to 56K; (so far I have not made the resistor change). Everything went well, no issues at all. I plugged in my Les Paul and let her rip, success was mine! It took me about 5 hours over two days to complete the installation. I took extra time with all the steps to avoid mistakes and sloppy soldering. I am sure an expert can complete this job in about two hours.
In summary, this was a great project for several reasons. I learned a lot about the inner-workings of a guitar amplifier and my amps no longer intimidate me. I am one step closer to my goal of modifying my JTM-45 to vintage specs. I also learned that good old-fashioned quality and customer service still exists in the 21st century. George Metropoulos at Metropoulos Amplification has provided a source for anyone ready to modify his or her Marshall with a point-to-point circuit board. The components and workmanship are excellent and the information and help resources make it possible even for a rookie to achieve success on the first try! I highly recommend Metropoulos Amplification for your PTP needs. I can honestly state that dealing with Metropoulos Amplification has been a pleasure from start to finish and the product and results far exceeded my expectations.
In part two, I will take the final steps to modifying my Marshall JTM-45 reissue to vintage specs. I will then compare the modified reissue amp head-to-head with a vintage Marshall JTM-45 and see just how close we can get to that Holy Grail of tone without going to the poor house.
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