snshami
Member
Just thought I would start a thread on a new journey I have just started on.
I own a Marshall DSL40c that I just love. For a month now I had been looking at getting a second amp my son can use so we can jam. After looking at many amps including a Vox AC10 and Blackstar HT20 I stumbled upon this beauty, a JTM60 with 3 10" Eminence drivers that someone had advertised on Gumtree for A$800.
The price was negotiable. The person, a guitar teacher and a top bloke, had gotten the amp in a non working state from a friend and had gotten it repaired by Clingan Guitars in Fitzroy. It got a new rectifier unit and two new power tubes. It also got a good clean and service.
I asked him for his best price and he told me about A$500.
Anyway after researching the amp and discovering that they needed some mods to run reliably I decided to offer A$350. Clingan told me the mod would at least be $120 if not more.
I got a feeling that he had too many amps and that the amp had not really cost him much to repair. Anyway he accepted my offer.
I brought the amp home and had a play with it. It was close to midnight so we ran it at bedroom levels. After about 15 minutes I could feel that left metal bit on the handle starting to get quite warm.
When I looked at the amp and saw how simple the layout was I decided to try the plate mod myself.
Next day I bought some aluminium plate and to cut a long story short I added the plate above and to the left of the power tubes so heat from the tubes no longer directly goes to the transformer or the electronic components above the tube.
I tried a modified version of some of the ideas I had seen and read about on the internet.
My shield is attached to the underside of the grille that forms part of the floor of the head. I did not need to drill any holes and instead bolted to the grille using washers to retain the nuts. I used around 2mm thick black powder coated aluminium plate that I scuffed, on the side facing the tubes, to a very matt finish. I removed the powder coating on the top side and polished it using 2000 grit sand paper till it was shiny and reflective. I used rubber grommets to insulate the bolts from the plate and to provide a standoff to the underside of the head unit of about 2.5mm. The width of the plate is exactly the right dimension so it makes a firm contact with the tube cage when I put that back on.
My logic is that the matt black finish facing the tubes will pull heat from the tubes and spread it evenly across the aluminium material. (I did not want the plate to reflect the heat back onto the tubes). The shiny top surface will inhibit radiation into the head unit. The size of the plate and the fact that it is in contact with the cage means that heat is spread evenly through the cage and into the whole chassis of the amp. Because it is now a very big heat sink very little heat will rise in the form of convection.
In order to do this I had to remove the amp head from the plywood housing (I think it is plywood). This showed me a few things. Firstly the PCBs, wiring and all other componentry showed no sign at all of heat damage. The wires were not brittle or discoloured and the PCB looked in a pretty good shape. I also realised that to a large extent the hysteria about the capacitors being directly above the tubes is complete nonsense. They are not. The underside of the head (its floor) has a grille portion. The tubes are below the grille and vent directly into the head unit. The reason for the grille is not immediately obvious. Maybe at some stage there was meant to be a vent at the top of the amp. The electronics are above the solid part of the floor. No electronic components are directly in the path of convective currents. At the most they would receive some radiated heat off the power tubes.
Of course the fact that the tubes vent hot air into the head electronics and the fact this hot air has nowhere to go does not make very much sense. I can just speculate that this was not meant to be one of the main products that Marshall produced in that era and it might not have had enough money for R&D. Maybe there was negative feedback against using vents on top of amps and maybe they did their testing on a cold winters day. Regardless of the reason, it is not an optimal design.
Another point is of course that even though the tubes can get upto 70 degrees (or 160F) that is below the heat capacity of rubber, plastic, PCB materials and electronic components. It is true that heat affects electronic components and that there is an inversely proportional relationship between heat and life of components but still this amp would have had a mean rated life of over 10 years for a gigging musician.
I think the number of people who came across issues would be small but justifiably vocal because there is no doubt that heat will increase the warranty and repair rate.
Anyway back to my amp. After testing for 30 minutes the top handle was completely cool and the cage was very uniformly, but very manageably, warm. The heat is now managed very well.
The amp has Sovtek 6L6 power tubes installed and is otherwise in great condition so I feel that for A$350 I have gotten the bargain of the century.
I have not yet had a chance to really listen but whatever I have heard impresses me a lot. My very quick first impression suggests it is more laid back than the DSL40c and lacks some of that amp's bottom end which is surprising given that the 3x10 drivers equal 2x12 so it should be pumping twice the amount of air that the DSL does. The JTM does not cover the tonal range that the DSL40c does, which goes into insane territory with hot enough pickups.
Of course this was playing both at very low volume. Both amps are of course very different. The JTM has a master volume and I need to get used to that. Also there will need to be some familiarisation time. I am sure over the days I will learn and discover a lot.
I will add images and my further impressions over the next few days.
Apologies for the long post and am happy to hear from other JTM owners, present or past.
Does anyone know how much this amp would have cost in 1995. It cannot have been cheap with all the features and being made in England. I have heard people call it a budget model which is surprising given it has 3 US made Eminence drivers, separate EQ channels, two effects loops, a DI out, both before and after the power amp and its made in England.
I own a Marshall DSL40c that I just love. For a month now I had been looking at getting a second amp my son can use so we can jam. After looking at many amps including a Vox AC10 and Blackstar HT20 I stumbled upon this beauty, a JTM60 with 3 10" Eminence drivers that someone had advertised on Gumtree for A$800.
The price was negotiable. The person, a guitar teacher and a top bloke, had gotten the amp in a non working state from a friend and had gotten it repaired by Clingan Guitars in Fitzroy. It got a new rectifier unit and two new power tubes. It also got a good clean and service.
I asked him for his best price and he told me about A$500.
Anyway after researching the amp and discovering that they needed some mods to run reliably I decided to offer A$350. Clingan told me the mod would at least be $120 if not more.
I got a feeling that he had too many amps and that the amp had not really cost him much to repair. Anyway he accepted my offer.
I brought the amp home and had a play with it. It was close to midnight so we ran it at bedroom levels. After about 15 minutes I could feel that left metal bit on the handle starting to get quite warm.
When I looked at the amp and saw how simple the layout was I decided to try the plate mod myself.
Next day I bought some aluminium plate and to cut a long story short I added the plate above and to the left of the power tubes so heat from the tubes no longer directly goes to the transformer or the electronic components above the tube.
I tried a modified version of some of the ideas I had seen and read about on the internet.
My shield is attached to the underside of the grille that forms part of the floor of the head. I did not need to drill any holes and instead bolted to the grille using washers to retain the nuts. I used around 2mm thick black powder coated aluminium plate that I scuffed, on the side facing the tubes, to a very matt finish. I removed the powder coating on the top side and polished it using 2000 grit sand paper till it was shiny and reflective. I used rubber grommets to insulate the bolts from the plate and to provide a standoff to the underside of the head unit of about 2.5mm. The width of the plate is exactly the right dimension so it makes a firm contact with the tube cage when I put that back on.
My logic is that the matt black finish facing the tubes will pull heat from the tubes and spread it evenly across the aluminium material. (I did not want the plate to reflect the heat back onto the tubes). The shiny top surface will inhibit radiation into the head unit. The size of the plate and the fact that it is in contact with the cage means that heat is spread evenly through the cage and into the whole chassis of the amp. Because it is now a very big heat sink very little heat will rise in the form of convection.
In order to do this I had to remove the amp head from the plywood housing (I think it is plywood). This showed me a few things. Firstly the PCBs, wiring and all other componentry showed no sign at all of heat damage. The wires were not brittle or discoloured and the PCB looked in a pretty good shape. I also realised that to a large extent the hysteria about the capacitors being directly above the tubes is complete nonsense. They are not. The underside of the head (its floor) has a grille portion. The tubes are below the grille and vent directly into the head unit. The reason for the grille is not immediately obvious. Maybe at some stage there was meant to be a vent at the top of the amp. The electronics are above the solid part of the floor. No electronic components are directly in the path of convective currents. At the most they would receive some radiated heat off the power tubes.
Of course the fact that the tubes vent hot air into the head electronics and the fact this hot air has nowhere to go does not make very much sense. I can just speculate that this was not meant to be one of the main products that Marshall produced in that era and it might not have had enough money for R&D. Maybe there was negative feedback against using vents on top of amps and maybe they did their testing on a cold winters day. Regardless of the reason, it is not an optimal design.
Another point is of course that even though the tubes can get upto 70 degrees (or 160F) that is below the heat capacity of rubber, plastic, PCB materials and electronic components. It is true that heat affects electronic components and that there is an inversely proportional relationship between heat and life of components but still this amp would have had a mean rated life of over 10 years for a gigging musician.
I think the number of people who came across issues would be small but justifiably vocal because there is no doubt that heat will increase the warranty and repair rate.
Anyway back to my amp. After testing for 30 minutes the top handle was completely cool and the cage was very uniformly, but very manageably, warm. The heat is now managed very well.
The amp has Sovtek 6L6 power tubes installed and is otherwise in great condition so I feel that for A$350 I have gotten the bargain of the century.
I have not yet had a chance to really listen but whatever I have heard impresses me a lot. My very quick first impression suggests it is more laid back than the DSL40c and lacks some of that amp's bottom end which is surprising given that the 3x10 drivers equal 2x12 so it should be pumping twice the amount of air that the DSL does. The JTM does not cover the tonal range that the DSL40c does, which goes into insane territory with hot enough pickups.
Of course this was playing both at very low volume. Both amps are of course very different. The JTM has a master volume and I need to get used to that. Also there will need to be some familiarisation time. I am sure over the days I will learn and discover a lot.
I will add images and my further impressions over the next few days.
Apologies for the long post and am happy to hear from other JTM owners, present or past.
Does anyone know how much this amp would have cost in 1995. It cannot have been cheap with all the features and being made in England. I have heard people call it a budget model which is surprising given it has 3 US made Eminence drivers, separate EQ channels, two effects loops, a DI out, both before and after the power amp and its made in England.
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