Quote from: RookieRecurve on April 09, 2024, 09:39:06 PMGreat explanation of why tubes are still so popular.  Its also a great reminder that great tones from inexpensive SS stuff can be had with the right piece(s) of equipment in front of it.  Sometimes I like to just plug into my fairly stock Valve Jr. and appreciate its simplicity, but other times I love playing around with different tools.  Your talk about having a tube in the signal path makes a ton of sense.  Thanks!

Crate really screwed themselves going back nearly 30 years ago when they started producing the cheapest solid-state amp line on the market, and because they were releasing the BlueVoodoo soon, they omitted the midrange control from their dirty lead and rhythm shared EQ. For their scale of production, we're talking a 10 cent pot replaced with a 1/20 of a cent 100 ohm resistor. Fundamentally, every reputable amp's midrange control coupled with a "legendary" speaker scoops the midrange deeply, and what they did was remove this control and replace it with the "shape" that is an active band-bandpass that sweeps it's cornered frequency while cutting or boosting while you rotate it.
You hear the amp, and initially they sound amazing, until you hear something that truly does lol. Then you hear the GLX which has the midrange coupled with the shape control, and it's one of the best metal amps you've ever heard, especially when paired to the right pedal. I own a GLX, and 3 GX amps, 2 of which are the same heads.
I scored this insane deal for $150 last night, and will mod the preamp to add the midrange EQ...the deal was only the Crate gear, not the valve-state Carvin V3 lol.

In regards to the science explained in simple language everyone can understand, I would probably churn out 50 paragraphs, but there's a decent redacted version. When a tube is pushed into overdrive and clips, it does 3 specific things. It obviously clips the signal producing distortion, it produces soft clipping so the edges of the wave's knee where the bandwidth cuts off and declines in magnitude is rounded, as are the mini-waves when zoomed in that comprise the entire waveform, and it cuts off bandwidth organically.
In general, a 12AX7 peaks out in typical operational bandwidth at about 20Khz in the audio spectrum, but it's actually more typical that it has a steep cut-off at about 10Khz. The soft clipping also results in an abundance of low, even order harmonics and by order we're regarding bandwidth so you hit a 100 Hz range bass note, and you aren't hearing a "crust" of 10Khz bolding within it let alone 20Khz, 40Khz etc.

What semiconductors do when driven into clipping is usually but not always, produces hard clipping so the waveform reproduction curve has a sharp edge at the bandwidth drop-off point of response and the mini-waves the entire waveform is comprised of also have sharp edges, and the bandwidth response/reproduction curve is massive. It will go out into 50 and 60Khz. If the circuit architecture isn't designed so it produces asymmetrical clipping, you get an abundance of dominant, odd order harmonics. These sound sleazy, sour but oddly very pleasing, and all around harsh. You hit a 100 Hz range bass note and you're hearing 13Khz, 27Khz etc; high, odd order harmonics due to semiconductor's organic bandwidth. It's literally the nature of the material at the quantum level due to speed of it's materials under electrical pressure.
When you design solid-state or for that matter, digital that uses semiconductors to clip asymmetrically, now it's even order harmonic dominant, but it's still high magnitude even order harmonics. So, you hit a 100 Hz range bass note, and you're hearing 10 Khz, 20Khz etc. content in it, which sounds more or less like static, swooshing and white noise.
People will often use an EQ pedal on solid-state gear and run a 12AX7 somewhere in their signal chain, and this greatly improves upon reducing the high even order harmonics because the valve naturally incorporates some low-pass filtering to remove some of that content in the signal, adds low even order harmonics, and some rounded clipping.

I'm here obviously because I love solid-state amps. Overall, I find they have much better modern characteristics than 90% of valve circuits which is why most every player uses a solid-state pedal in front of their tube amps. I prefer the sleaze, raunchy, in your face thrash metal sound, but also despise that high, even order harmonic content so it's the tradeoff you face in tube vs solid-state. At this current time though, I am designing my own gear from the ground up, and only just made my last few purchases because I have a pile of gear in need of minor repairs and some crazy famous b*t** I prefer not to name smashed my Zoom G5 modeler which just happens to have a 12AX7 in it, and sounds great on my tube amps, but significantly better on the solid-state.

(I had to order that all the way from Japan, but even at 12 years old, it sounds better than the 2023 Valeton flagship model I have, the flagship model Headrush I returned after a few weeks which was a 3-legged dog, and I would put it up against the $500 PODs for that matter. That valve at the end of the digital chain makes a massive difference, but even with it switched off, it sounds much better than what was released in the last 5 years from virtually everyone and this is from having tried or temporarily owned their gear.)

The first thing I sat down to do recently was design a transistor-based distortion without diodes by overdriving the transistors into clipping organically and asymmetrically which not only sounds indiscernible from tube distortion, but obviously better when you hear the right circuits. This is where I can just keep rambling on since this recent task has been ongoing for about 20 years starting when I was an ignorant amateur modding and building gear 20 years ago, and finally enrolled in college for the science of electrical and electronics engineering 13 years ago. I'm unsure if I can truly bring my creations and inventions to the commercial market through my own manufacturing scheme or licensing if not selling designs, but I know I can produce something superior to everything up to this point that should be a huge leap in analog and outperforms both vacuum-state and solid-state. Overdriven transistors produce a fuzz style distortion that sounds interchangeable to overdriven valves, and there's a ridiculously simple solution to resolving the excessive upper range bandwidth magnitude of even order harmonics that makes *s!!t* raspy, crusty, swooshy, sloshy and also adds that white noise hiss everyone has grown to loathe about solid-state, and for good reason.

That's another series of ranting paragraphs in itself about my belief as to why major mfr. have done very little about it until recent years, it's only just been in digital semiconductor designs, and they still haven't completely resolved it. The short story there is I think it's a mixture of ignorance due to the nature of engineers that have advanced educations and are thinking in terms of numerical value vs actual organic performance that satisfies human hearing, and some that know maintaining a bit of these short comings ensures their tube lines keep luring in massive pools of customers and in the grand scheme of commercial manufacturing, they're making the most dependable and consistent profits off valves. Majority of players will eventually turn to valves and primarily depend on them over semiconductor technology.

Anyway, with my current goal, it seems the most realistic product I can design and potentially get onto the commercial market is a signal conditioner that wipes out high order harmonics even and odd and wipes out 60-cycle hum and other RF noise whether it's getting into your single coils, your pedals, your wires or even into your humbuckers. One of the the specific things I achieved as a blindly experimenting amateur was my overdrive I designed from the ground up to replace my dissatisfactory tube screamer wiped out all the ground buzz but didn't significantly compromise the upper bandwidth range we still desire to hear, especially regarding even order harmonics. With these goals, I'm primarily focused on a full fledged preamp that will eventually get a power stage, and a signal conditioner to go on the effects loop to wipe out noise without signal compromise, and also get rid of the hiss, slosh, rasp and static-like sound of semiconductors so ever present in majority of digital and solid-state gear.

Quote from: Tassieviking on April 15, 2024, 02:49:34 PMHave a look at the last layout for the JC-120, it shows the layout of the same PCB I think.
The JC-120 appears to be 2 lots of JC-60 amps in one box.
This is the closest I have on that amp.

Perfect, thank you!
i'm going to check the values of the components and compare them to the ones on my jc-60 later to verrify that, but the layout seems identical.
Thank you a lot!

Have a look at the last layout for the JC-120, it shows the layout of the same PCB I think.
The JC-120 appears to be 2 lots of JC-60 amps in one box.
This is the closest I have on that amp.

ok i found an older service manual for the jc-60 #512400 (and higher) from june 1977.
it even includes a wiring diagram and a components layout for the jc-60 #481650-#502399, but it's still not the right version.
Does anyone have an idea where I can find the correct version?

Quote from: Jazz P Bass on April 15, 2024, 10:56:14 AMYour serial number indicates a manufacture date of June of 1975.
The schematics that you found are from 78 & 79.

Thank you for the info about the manufacture date! Seems to be the first version of the JC-60 then. I read somewhere that they started building the jc-120 and the jc-60 in 1975.

Your serial number indicates a manufacture date of June of 1975.
The schematics that you found are from 78 & 79.

Quote from: g1 on April 14, 2024, 02:44:32 PMThe service manuals usually go by serial number, what is it?

The serial number of the amp is #430830.
In the service manual is a note that for the JC-60 its for #787100- and for the JC-60A R&P its for #810530-. It was first printed on March 31. 1979 and its the fourth edition.
The amp is a earlier version, it has a different circuit board, different power transistors and has less control inputs on the back. i couldn't find the right service manual for my version. just the one mentioned and newer ones.
Does anyone maybe have an earlier service manual?

Quote from: saturated on April 14, 2024, 01:45:56 PMWow nice amp 

Welcome to the forum

 

Thank you!
 

The service manuals usually go by serial number, what is it?

Wow nice amp 

Welcome to the forum