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Author Topic: JTM-18  (Read 22315 times)
JohnA
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« on: January 28, 2010, 07:14:36 AM »

With a bit of help (OK a lot of help) from Nik, the guys at 18watt and PP forums I've put together an amp that fits my needs perfectly.  I love the sound of my Ceriatone JTM-45, but with the band I play with it was just far too loud, I used to rehearse with my cab facing the wall, and surrunded by drum cases!!

So with a JTM-45 board with a few resistor tweaks, a set of 18W transformers and a pair of 6V6's I've managed to capture the vound of my JTM45 in a lighter, smaller and most importantly quieter package!  The amp still kicks out some serious giggable volume, but I can get in to AC-DC crunch territory without deafening eveyone!

So thanks Nik, and the others that provided help, and here's a few pics Grin




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StringSkunk
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« Reply #1 on: March 15, 2010, 09:17:58 PM »

Hey that's pretty cool. You wouldn't mind letting me in on some of those tweaks and secrets would you? I feel like I could also really benefit from a quieter JTM45, well, my ears at least  Cheesy
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JohnA
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« Reply #2 on: April 18, 2010, 11:57:21 AM »

Sorry for the late reply, haven't been on the forum for a while.  Not too many changes actually,

Here's the layout, I used the ceriatone layout (it's actually a modified ceriatone board) with a few resistor changes on the advice of the nice people here, a EZ81 for the rectifier, valvepower 18W transformers, and a 7H choke fom bluebell audio, for the rest of it I followed the ceriatone Layout.  Oh the -ve feedback resistor is connected to the 8 ohm secondary on the OT rather than the 16 ohm on the JTM45 on the advice of Nik at Ceriatone, who's been a very big help with the project.

« Last Edit: January 30, 2011, 02:19:19 PM by JohnA » Logged
bertonguitar
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« Reply #3 on: October 01, 2010, 08:12:10 PM »

Hello StringSkunk,
Based on JohnA's project I asked Nik to build me a JTM with 6V6's too, Nik named it the JTM20. Killer amp just like my other Ceriatones. I've playing the JTM20 with a Xotic BB+ preamp and Tonebone Plexitube and honestly, the sound is insane. Been playing for 30+ years and hands down this amp and my Creme Brulee are the best amps I've ever had.
All the best,
Bert
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Ceriatone OTS 50W, Creme Brulee, JTM20
Mesa 1*12" EV-12L
Weber 2*12" Eminence Texas Heat
Motion Sound SR-112 Leslie
cmoore
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« Reply #4 on: October 02, 2010, 12:42:35 AM »

I gotta say....I'm impressed. It is not cat biased AND it does not use EL84's, that is kind of a breath of fresh air IMO. A real nice looking amp, all the way around.
It looks like a Hammond choke....
Who made the PT and OT...?
Thank You
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JohnA
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« Reply #5 on: October 07, 2010, 01:09:08 PM »

Thanks very much!  yes every other 18W variant seems to use EL84's and be cathode biased, the cleans on this one are far sweeter that a 'regular' 18W  It's still my #1 amp
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Tone Control
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« Reply #6 on: October 23, 2010, 03:47:30 AM »

so this is much closer to the JTM45 sound and feel than the EL84 amps?
Certainly the Cornell 18/20 I own sounds quite different to my JTM45

Does the EZ81 supply the power in the same way as in the JTM45 (i.e. same balance of sag and attack). To me the JTM45 has very fast attack for an old amp design's tube rectifier
I ask since the Cornell 18/20 I own sounds very soft on the tube rectifier, and I often need to use the SS rectifier

So I suppose I'm asking - does it really sound like a JTM45 and does it need switchable rectification if made with an EZ81?

Cheers
Tone
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Dr Tone Control, Strats mostly, prefer saturated clean tones, a little OD sometimes
BM50, JTM45, 36w EF86, DZ30, Expression, + non-Ceriatones (Matchless, Victoria, Wienbrock)
Just started with pedals a little after a 10 year purist spell, but usually just delay
JohnA
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« Reply #7 on: October 31, 2010, 01:41:32 PM »

It's actually very like a JTM45, I have a ceriatone JTM to compare.  It has a little more gain when wound right up, gets in to Plexi territory, heres a clip of it on 10, but it cleans up a lot better than most 18W and has quite a bit of clean headroom

http://www.youtube.com/user/AireSound#p/u/14/1M15Ql8UE4c

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Tone Control
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« Reply #8 on: October 31, 2010, 07:13:47 PM »

It's actually very like a JTM45, I have a ceriatone JTM to compare.  It has a little more gain when wound right up, gets in to Plexi territory, heres a clip of it on 10, but it cleans up a lot better than most 18W and has quite a bit of clean headroom

http://www.youtube.com/user/AireSound#p/u/14/1M15Ql8UE4c



Sounds interesting
I can't really judge it from the audio in that video
My favourite sound on the JTM45 is my strat neck pickup , Treble #1 input, set to vol= 7-8
I get this lovely touch sensitive zone
With humbuckers & turned up to 10, the grit comes too, but that 7-8 strat sound is my favourite

Can the 6v6 amp do that?

Cheers
Tone
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Dr Tone Control, Strats mostly, prefer saturated clean tones, a little OD sometimes
BM50, JTM45, 36w EF86, DZ30, Expression, + non-Ceriatones (Matchless, Victoria, Wienbrock)
Just started with pedals a little after a 10 year purist spell, but usually just delay
JohnA
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« Reply #9 on: November 02, 2010, 06:57:35 PM »

The 'JTM-18' is as close as you will get to a JTM45 without the weight or volume, where are you located?  You would be more than welcome to try it, I'm in the North of England
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JohnA
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« Reply #10 on: January 28, 2011, 03:39:04 PM »

I gotta say....I'm impressed. It is not cat biased AND it does not use EL84's, that is kind of a breath of fresh air IMO. A real nice looking amp, all the way around.
It looks like a Hammond choke....
Who made the PT and OT...?
Thank You

Sorry for the late reply, only just seen the question.  Yes it's a hammond 159Q choke, the PT & OT are 'valvepower' ones made in the UK, cheapest iron available, and sounds great!
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JohnA
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« Reply #11 on: January 28, 2011, 03:42:22 PM »

Hello StringSkunk,
Based on JohnA's project I asked Nik to build me a JTM with 6V6's too, Nik named it the JTM20. Killer amp just like my other Ceriatones. I've playing the JTM20 with a Xotic BB+ preamp and Tonebone Plexitube and honestly, the sound is insane. Been playing for 30+ years and hands down this amp and my Creme Brulee are the best amps I've ever had.
All the best,
Bert

I bet Nik made a neater job than I did Wink  would love to see some pics
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Fatknuckle
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« Reply #12 on: September 24, 2013, 05:20:24 PM »

Along these lines, I recently built one as well.  It dissipates 11.8 watts per tube..so I call it a JTM-22-1/2.  Great Brit tone and crunch, and still quite loud at higher volumes.  I also installed a Lar-Mar Post Phase Inverter Master Volume, with the control on the rear.  I used a 100k linear dual pot in place of the 100k bias resistors.  Getting ready to build the head cab this weekend.


* JTM-22.5.JPG (512.53 KB, 1632x1224 - viewed 842 times.)
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