Ceriatone JTM45 Bluesbreaker Kit

Chris-in-LA

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I thought that Ceriatone wasn’t doing kits anymore. Apparently that’s not true. I’ve been looking for a 30 watt JTM45 almost since I’ve been building kits. I did a search last night for one and this came up. I’ve been wanting a 30 watt Marshall for some time as my 50 watters can be damn loud, the 1987x Plexi just isn’t tolerated by most people. But I really like the way the 4 holers cut through. I think 35 watts will be just about right. I can crank it and use a boost if I need more gain. I’m also finding that having less gain makes for a more responsive amp.

https://www.flickr.com/photos/[email protected]/28465013654/in/album-72157671479102100/

I emailed Nik and he confirmed that they were selling this kit. So, I ordered one minus the cab and tubes, $700. I paid for it by Paypal before I read the fine print where Nik said that I might want to wait to pay as they are all locked down over there. So much for another quarantine project.

it does look like a nice kit and even has a half power switch. I’m looking forward to this one.

https://www.flickr.com/photos/[email protected]/29053416136/in/album-72157671479102100/
 

neikeel

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I think that the Ceriatone stuff (at least that I bought) was pretty decent but to a specific price point.

If you wanted quality more akin to an original then I would say go Valvestorm.

Having said that I see on the pics of the Trem amp guts you posted he has gone for a more vintage era correct look with the dark board, turret style, Belton sockets. Looks like a couple of tweaks with simple interrupt effects loop, external bias adjust, rotary imepedance selector and half power switch. All simple sound mods.

Should be a fun project (beware there will be no instructions but layouts are pretty clear)
 

Chris-in-LA

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I think that the Ceriatone stuff (at least that I bought) was pretty decent but to a specific price point.

If you wanted quality more akin to an original then I would say go Valvestorm.

Having said that I see on the pics of the Trem amp guts you posted he has gone for a more vintage era correct look with the dark board, turret style, Belton sockets. Looks like a couple of tweaks with simple interrupt effects loop, external bias adjust, rotary imepedance selector and half power switch. All simple sound mods.

Should be a fun project (beware there will be no instructions but layouts are pretty clear)
The main reason I went with this kit is because it’s the first one I’ve seen that’s not listed as being 45 watts, I’ve been looking for one in the 30 watt range.
Have you seen the layout for this? Tell me how the half power switch works.

http://www.ceriatone.com/ceriatone/wp-content/uploads/2016/12/JTM45-BB-1-Dec-2016.jpg
 

Chris-in-LA

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I’m thinking about leaving out the passive loop for now as I almost never use one. First step will be drilling the holes in the head box for the chassis. I ordered the cabinet from Sourmash and it came at the same time as the kit by coincidence. They even sent a t-shirt with it. Pics to follow.
 

Chris-in-LA

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I’m using this wiring layout. I plan to run a wire from Q on the board to the E on the treble pot to bypass the loop for now. Can anyone see a problem with that?

upload_2020-5-19_3-46-9.jpeg
 

neikeel

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Looks good to me.
That wire between pi and treble is normal on 4-holers without MV or loop.
Consider 470k mixers where the two channel volume wipers merge (vs 270k). It gives more grit and grind.
 

Chris-in-LA

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Looks good to me.
That wire between pi and treble is normal on 4-holers without MV or loop.
Consider 470k mixers where the two channel volume wipers merge (vs 270k). It gives more grit and grind.
Good to know.
 

Chris-in-LA

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Was working on wiring up the power section and had to ask Nik why the tube rectifier has diodes attached. He said it’s to protect the tube from an inrush of current. The PT has a 50v tap that isn’t used, seems a little odd.

upload_2020-5-22_23-21-53.jpeg
 

Chris-in-LA

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The diodes protect your PT should your rectifier die. The 50 volt tap was for bias voltage.
The wiring layout shows 350+ going to a 180k resistor and into the bias circuit. Is that the best way to do it? I was wondering why they didn’t use the 50v.

Edited to add: I just checked the wiring diagram for my 2204 and they do a similar thing, but with a 150K resistor. So this must be an acceptable way of doing things.
 
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Chris-in-LA

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Wired up the tremolo board. I need to populate the main board, I have too many small parts in too many bags and need to cut down on the clutter.

upload_2020-5-23_9-1-53.jpeg
 

neikeel

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The wiring layout shows 350+ going to a 180k resistor and into the bias circuit. Is that the best way to do it? I was wondering why they didn’t use the 50v.

It is how Marshall did it and it seems to work pretty well (not the cause of historical PT failures in the early 70s!!).
If you do choose to use the 50v tap you would probably only need a 10k rather than the 180k in series before the diode, ground the other end wherever is convenient. If you do this take care to ensure that you have enough negative volts on pin 5 of your outputs when you do your pre-tube insertion tests, as if it is much too hot you will redplate and trash your output tubes quite quickly even without load.
 

Chris-in-LA

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It is how Marshall did it and it seems to work pretty well (not the cause of historical PT failures in the early 70s!!).
If you do choose to use the 50v tap you would probably only need a 10k rather than the 180k in series before the diode, ground the other end wherever is convenient. If you do this take care to ensure that you have enough negative volts on pin 5 of your outputs when you do your pre-tube insertion tests, as if it is much too hot you will redplate and trash your output tubes quite quickly even without load.
Good to know. I’ll probably stick with their layout for now. BTW, the 270k mixing resistors are reading closer to 290k. I was worried until I remembered what you said about being able to increase them to 470k.
 


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