#1
I love reading about guitar amps, I like learning about their history, how they were designed etc. Seems like most amps I've read about are based on Vox, Fender or (in most cases especially the higher gain area) Marshall. One thing that's stuck out at me is I don't know I've ever read about an amp based on a Mesa/Boogie design and that surprises me given Mesa's impact sonically in Rock music especially over the last 20 years. Having a Fractal Audio Axe FX II has heightened my enjoyment of reading about amps, since it's gotten so close that it's really the next best thing to playing the real amp and probably the closest I'll come to playing many of them. If any one would like to share any knowledge you have on amps and their designs, your experience and thoughts on the amp, possibly any settings and any tips or tricks I'd love to read them and appreciate the input. Thanks guys!
Last edited by stm113 at Mar 6, 2016,
#3
pretty much all tube amps stem from the original RCA circuit made about
90 yrs ago
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#4
And what is original anyway?
The old Fenders were just rehashed RCA circuits.
The Mesa Boogies were modified Fenders. The Mk1 is a Princeton with extra stages and a Bassman power amp.
The JTM45 Marshall was a rehashed Tweed Bassman.
Pretty much everything can be traced back to the old RCA circuits.


Edit. Ninjad by Rob.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Mar 6, 2016,
#6
It's not RCA amps specifically. It's RCA circuits that were produced with their tube datasheets.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#7
mesa's are all based on fenders for the most part.
Jumping on dat gear sig train.
PRS Hollowbody II / BKP Warpigs
Strandberg OS6T / BKP Aftermath
Strandberg OS7 / Lace Poopsticks
Skervesen Raptor 7FF / BKP Warpigs
Skervesen Raptor 6 NTB / BKP Juggernauts
Hapas Sludge 7 FF / Hapas Leviathan
Anderson Baritom / Motorcity Nuke BKP Sinner Anderson H2+
Warmoth Baritone / BKP Piledriver
Ibanez Rg2120x / BKP Nailbomb

Blackstar ID:Core Beam
#8
Tubes them selves don't support a lot of different circuit design. Most amp differences are in the (passive) tone control circuits chosen.
Moving on.....
#9
As for the AC15/30. They aren't based on any other guitar amp really. The preamp uses RCA designs but tailored to fit the Phillips designs for the EL84's which were very new at the time. EL84's are far more sensitive, resulting in a far simpler preamp.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#10
There's not a lot of difference in the power amps at all. For example, Marshall essentially changed power tubes whenever one became difficult to get in the UK or too expensive and went through almost everything.

Most of the differences came in minor modifications of the tone stack in the preamp section. The magnetic pickups use in electric guitars are very mid-centric, and in order to balance them to any degree, a healthy mid scoop is designed into *every* guitar amp. The placement of that mid scoop will often distinguish one amp's characteristic sound from another.

For example, Fender placed its mid scoop lower in the mids than Marshall's. This gave Fender amps a much brighter overall characteristic. Jim Marshall moved the mid scoop higher on the scale, which gave his amps more low-mids response.

#12
Quote by Fumble fingers
the RCA circuit was for radio's


Was there a point here?
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin
#13
Quote by Arby911
Was there a point here?

Was there a point here?
Quote by Cathbard
Quote by Raijouta
Unless its electronic drums.

BURN THE WITCH!!!!!
#14
Quote by tubetime86
Was there a point here?


The RCA circuit was for radios? So?

The RCA manual (R10) speaks at length about "radio tubes" because that's what they called them but there's an entire section on amplifiers.

I could have assumed that the post I responded to might indicate that they think the RCA circuits aren't relevant because of the nomenclature used, but I chose to ask instead of assume.

Hope that helps?
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin
Last edited by Arby911 at Mar 7, 2016,
#15
Quote by Cathbard
As for the AC15/30. They aren't based on any other guitar amp really. The preamp uses RCA designs but tailored to fit the Phillips designs for the EL84's which were very new at the time. EL84's are far more sensitive, resulting in a far simpler preamp.
How neat. So really the only two original amp circuits (excluding the RCA) were Fender and VOX?
#16
Quote by Will Lane
How neat. So really the only two original amp circuits (excluding the RCA) were Fender and VOX?


I'm not sure we should even consider them "original".

If you take a BLT and change the amount of lettuce and the brand of bacon, it's still a BLT.
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin
#17
Quote by Arby911
Was there a point here?

Perhaps the point was that since Will was unable to find any "RCA amps" it might be because he was barking up the wrong tree.

On the other hand, searching for "RCA amplifier circuits" pulls up plenty of familiar examples so I'm not sure why that was hard to find for Will. This stuff is pretty well documented.
Quote by Arby911
I'm not sure we should even consider them "original".

If you take a BLT and change the amount of lettuce and the brand of bacon, it's still a BLT.

I agree. If Fender and Vox are "original" then so are a whole lot of other ones based on those. There aren't that many ways of skinning this cat, and the RCA manual outlined the most fundamental ones from which all others derive in some form or another.

I think at some point this conversation requires a bit of familiarity with the circuits, which is where Will might be having trouble. A primer in amp circuitry makes this a much easier idea to understand. Otherwise it sounds like RCA "invented" the guitar amp and everybody else either copied it or invented a new one, which isn't the case but is tough to explain without being able to reference the schematics.
#18
Quote by Roc8995
On the other hand, searching for "RCA amplifier circuits" pulls up plenty of familiar examples so I'm not sure why that was hard to find for Will. This stuff is pretty well documented.
I guess I am search engine deficient. I typed in "RCA guitar amp" and did not get much for documentation but demos of some old amps and people asking "what is this?"
#19
At the heart of it, a guitar amp isn't an incredibly complex device. Modern amps are a bit wild with all their switching options and all the extra doodads thrown in, but the signal path is simple enough.

Probably the biggest innovation was cascading gain stages, and that got thought up a while ago.
I'm just a kickin' and a gougin' in the mud and the blood and the beer.
#20
Quote by Will Lane
I guess I am search engine deficient. I typed in "RCA guitar amp" and did not get much for documentation but demos of some old amps and people asking "what is this?"

You can't find an RCA guitar amp for the same reason that you wouldn't find any references to World War One in a newspaper from 1925.

This is where the radio comment is relevant. They weren't specifically guitar amps, they were just amplifiers. If you google RCA amplifier circuits you'll find a bunch that look an awful like guitar amps because in a sense they are. They were guitar amps before there was such a thing as a guitar amp - they just had "amplifier" circuits and you plugged whatever needed to be louder in one end and a speaker into the other. So of course they weren't called guitar amps, just like World War I wasn't called that until they had a second one. The RCA circuits were just the building blocks for what turned into guitar amps, microphone amps, keyboard amps, bass amps, phonograph and radio and TV amps. Different toppings, same pizza.

The urtext here is the RCA tube manual. They went through a bunch of editions but they've got the same basic information.
http://www.tubebooks.org/tube_data.htm

It's important to note that the RCA manual didn't invent all of this stuff, either. It was just a handy manual to their products like the recipes on the back of ingredients boxes. Pillsbury didn't invent baking, they're just telling you what to do with their dough. RCA certainly developed a lot of things but they didn't invent every circuit you see in the manual from scratch.
#21
thanks , that's what I meant by radio amp or public address PA ..... now days when you say amp I think guitar amp but that wasn't the case back then and why it took some tweaking to turn into a music amplifier
#22
To confuse things further, even amps that we think off as dedicated guitar amps today were often used as all-purpose amplifiers in the past. Look at the Fender tweed Deluxe for example, it has four inputs and two of them say "MIC".

People plugged all kinds of stuff into those amps. This might also explain why even early "guitar" amps have much more gain then you'd need to reach maximum un-clipped output with any given guitar. All that gain was probably pretty useful for very weak signals, like from ribbon-mics and such.

Entire bands sometimes played through a single combo (well, not the drummer I suppose). It sounded god-awful, but it worked.
#23
Guitar amps were made to be affordable, easy to produce, and sound good in that order.
That meant simple circuits that did the job using as few tubes as possible.

There's a lot of circuits in the rca hand book. 99 percent of guitar amps use 2 of them.
Jumping on dat gear sig train.
PRS Hollowbody II / BKP Warpigs
Strandberg OS6T / BKP Aftermath
Strandberg OS7 / Lace Poopsticks
Skervesen Raptor 7FF / BKP Warpigs
Skervesen Raptor 6 NTB / BKP Juggernauts
Hapas Sludge 7 FF / Hapas Leviathan
Anderson Baritom / Motorcity Nuke BKP Sinner Anderson H2+
Warmoth Baritone / BKP Piledriver
Ibanez Rg2120x / BKP Nailbomb

Blackstar ID:Core Beam
#24
So as has been stated, every amp is based on example circuits from the RCA handbook. People got bored of amps just reproducing what they put in though, so they started tinkering. That's how we ended up with different tonestack voicings and EQ center/turnover frequencies (interesting note, on guitar amps with 3 band EQs, the bass and treble controls are shelving filters and the mid is a bell filter, all with fixed Q and frequency values).


But most guitar amps are modified Fenders or Marshalls. Sure, there are some that are Vox based, but 90% of amps out there owe some heritage to someone getting bored and messing about with an amp they had lying around. Hell, the original Marshall is a modified Fender Bassman (different power tubes, chassis material, different tonestack). The original Mesa is a modded Fender Princeton running into a Bassman power section. Some boutique amps are based on the Vox circuits, but the number of Fender/Marshall inspired designs dwarfs them.

Most high gain amps can be traced back in some way shape or form to the Marshall JTM45. They're all based on it to some degree.
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You CAN play anything with anything....but some guitars sound right for some things, and not for others. Single coils sound retarded for metal, though those who are apeshit about harpsichord probably beg to differ.