JTM50

simeon

simeon

Axe-Master
Some JTM50's had solid state rectifiers. From online pictures at least some of Angus' heads were solid state rectified. Who knows which ones he used on the albums.

Experiment with the 50 watt plexi models and turn up the negative feedback. JTM45's and 50's had a lot of negative feedback making them cleaner and more punchy sounding than later plexi amps.
 
That's my new favorite amp tbh, it's the sound I've always wanted, and I'm considerng buying a Metro replica or something. I tried getting a similar tone by modding a JTM45 in the Axe but I couldn't quite get there, maybe bc there's no way to change some cap values. Or maybe I just suck at deep parameters.

Seems to be quite a strange beast tho, look at this video right here. The man is plugged into the normal channel, which should be extremely bassy (being a JTM), yet it is not.

 
dpeterson said:
Apparently looking like you are having a seizure helps the tone too?
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Will have to try that. Looking like you are constipated is deffo not working here.... 😁

Yeah, plexi with higher negative feedback is probably a good starting point as far as the amp is concerned. Getting the primary impedance specs for the plexi OT and the JTM50 OT would help, too, so a good starting adjustment could be made on that param as well....
 
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I have a JTM 45-clone that is switchable to JTM-50 spec. The modes are pretty similar. Get a bit more warmth and sponginess in 45 mode and a bit more volume in 50 mode.
 
GaryMcT said:
I have a JTM 45-clone that is switchable to JTM-50 spec. The modes are pretty similar. Get a bit more warmth and sponginess in 45 mode and a bit more volume in 50 mode.
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Maybe you could help us get closer using an existing amp model?
 
simeon said:
so apparently Angus used JTM50's on highway to hell

they do sound mighty fine...



basically a JTM45 with the following modifications...

784-139 OT with EL34s
1K 5W screen resistors
32uf x 32 uf internal can cap
dual 33uf on the board
2x470K resistors instead of 2x270K
tube rectified

http://site.triodestore.com/JTM50layout.pdf

https://solodallas.com/history-of-the-jtm50

can we tweak an existing model to get close?
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send Cliff the schematic and maybe we will get lucky he will work his magic and put it in the axe fx 3 amps
 
GaryMcT said:
A JTM-50 should have a solid state rectifier.
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Happily, we can choose in the AF3.

Quoting the article (https://solodallas.com/history-of-the-jtm50):

"During the development of the 100w amps, Marshall decided that the GZ34 rectifier tube wasn’t necessary. The first 100w heads were already made with solid state rectifier. This practice was to be adopted in the 50w amps later on. During this period, a Black Flag JTM50 could either have the GZ34 tube or be SS rectified. It wasn’t until later in 1967 that all the amps were SS rectified.

In summary, the Black Flag JTM50 generally has the following specs (not getting into details):
– Shared cathode;​
– JTM type tone stack;​
– EL34 power tubes (50w);​
– GZ34 tube or SS rectifier;​
– Bright cap on Vol I (on 1987 Lead model).​

For all the rest of the work, since Highway To Hell in 1979, JTM50s were always used. "
 
as a reminder, you can simulate the compander in the schaffer replica by running two dynamics blocks in series. set the threshold as low as it will go in both blocks, dynamics to -3 in the first block and +3 in the second with a bump in the level of the second block to goose the amp a bit.
 
I sure wonder how much raw volume there was in that room, given the feedback the guy was getting. It's easy to underestimate the role of the acoustic feedback in getting that feel, even at lower gains. The "Gain Enhancer" item in the dynamics section of the amp block seems to get a step closer, and a little goes a long way. But it seems like nothing really replaces that thick cushion of compressed and rarefied air between the cab and the guitar. Maybe once we get a little device like this to attach to our guitar we'll be able to get closer. But then you lose the feel of your pants legs shaking. Always a tradeoff.
 
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