TFF member Amp FAQ

[MMP]

EDIT by Moderator: As suggested, I turned this thread into a sticky and deleted some of the extraneous posts to make this thread a repository for amp info. Please don't ask amp questions in this thread, but we'd ask the amp gurus to add to it from time to time to make it a helpful reference source for amps. Thanks for your input!

--pc



(Original post text:)
Your amp is the voice of your guitar.
Do you feel that you need one special amp to get "your" sound? Or can you get it out of any ole amp that's around? When you get a new amp, do you spend the first three hours trying to make it sound like your old amp? Or do you search for what new sounds are available?
If it is only one, what amp voices your sound?

[JAM]

I've found a good jazz sound with my SS Fender with upgraded speaker so I've got that covered, and find that on my Vox AD30VT spend about 90% of the time on either of the two Fender amp models - the Black 2X12 (Twin) or Tweed 4X10 ('59 Bassman). I had a RI Bassman and sold it like a dumbass when the band I used it with fell apart.

Dont mean to hijack this thread but -
@Fezz and Kap'n - how similar in sound is a tweed (5E5, 5E7, 5F4) to the 5F6 Bassman? Seems with the different tone stack and long tail PI the Bassman is in class somewhere in between the Tweeds and BF Fenders. Yes? With Webers 10% off until 7/31 I'm really itching to try one of these.

[TT100]

I think you'll sound like you no matter what you plug into. It's in the hands right?

But, to get the sound you want, for the type of music and the venue, you might need more than one amp if you're not relying on the PA to mic and mix into a monitor feed for the band.

My old Pro Reverb does everything I could want from two 12s, Ted's 12F150s and a pair of 6L6s but I don't think it would be clean enough to do funk rhythm in a horn band if I'm standing next to the horns.

I don't have the need for one but I'd like to mess around with an old TR for fun.

Kap'n and Fezz are rightfully proud and satisfied with their Weber kits and I'm on my second DIY amp. A tweed super copy that I might get a chance to finish this week.

Dont mean to hijack this thread but -
@Fezz and Kap'n - how similar in sound is a tweed (5E5, 5E7, 5F4) to the 5F6 Bassman? Seems with the different tone stack and long tail PI the Bassman is in class somewhere in between the Tweeds and BF Fenders. Yes? With Webers 10% off until 7/31 I'm really itching to try one of these.

I thought about this last night. After putting down Teagle & Sprung's Fender Amps book, good as it is, it doesn't describe the different amp's character which is something frequently asked here.

How about it Lily & the Mods? Can we create a Tweed/BF/SF reference area that gives a brief description of each model's (and their variants) sound, volume etc?

TT

[Kap'n]

How about it Lily & the Mods? Can we create a Tweed/BF/SF reference area that gives a brief description of each model's (and their variants) sound, volume etc?

That could be cool. Something I think would be useful would be a construction of relative volume levels of these amps on clean and distorted scales assuming speakers of reasonable efficiency. As an example (incomplete, ovbiously).

Clean scale:
Tweed Champ
Champ
BF/SF Princeton
Brown Princeton
5E3 Deluxe
BF/SF Princeton Reverb
BF/SF Deluxe
BF/SF Deluxe Reverb
5F4 Super
5E7 Bandmaster
BF/SF Vibrolux Reverb
BF/SF Super Reverb
BF/SF Twin Reverb
Quad Reverb
Super Six Reverb

Dirty Scale
Tweed Champ
Champ
BF/SF Princeton
BF/SF Princeton Reverb
Brown Princeton
BF/SF Deluxe
BF/SF Deluxe Reverb
BF/SF Vibrolux Reverb
5F4 Super
5E7 Bandmaster
BF/SF Super Reverb
Twin Reverb
Quad Reverb
Super Six Reverb

[Kap'n]

Deciphering Fender Amp Circuit Revison Codes- The 50's/Early 60's

Fender amp circuts from the fifties and early 60's were given codes that refered to what the schematic was to build them. One thing to remember was that Leo was both a tinkerer and a frugal man. This means:

1. Sometimes what's in the amp doesn't match the circuit code listed.
2. Sometimes the circuit would change, but Leo would want to use up the old tube charts, where the circuit revision was listed.

To be absolutely sure what you have in an amp, you actually need to open it up and look at it. This also applies to the CBS years as well, since they never updated their tube charts, either.

Anyway, the key to this code is:

Digit: Decade of production
Letter: Circuit revision
One or two digits: Model of amplifier
"A" or "B" (opt.) Appended circuit revsion (like softwareversion 1.1)

Decade of production is always either a 5 or a 6, for, not coincidentally "50's" and "60's."

Letter refers to circuit revision. For amps that were around in 1951, when this code came into being, the first revision was "A," followed by "B" in 1952, followed by "C" in 1953. From here, it changes from indicating model year as well, to having larger intervals between changes. Additionally, amps introduced after 1951 didn't necessarily start with A for the first circuit revision. The higest letter commonly found in tweed amps is "F." G circuit revisions indicated white and brown tolex amps, no matter where letters were beforehand. Note, very early tolex amps made in 1959 still had listed "5" for the decade.

Model of amplifier. This followed the following code:

1 = Champ
2 = Princeton
3 = Deluxe
4 = Super
5 = Pro
6 = Bassman
7 = Bandmaster
8 = Twin
9 = Tremolux
10 = Harvard
11 = Vibrolux
12 = Concert
13 = Vibrasonic
14 = Showman
15 = Reverb unit
16 = Vibroverb

Examples:

5E3 would be a fifth circuit revision Deluxe made in the 50's.
5A4 would be a first circuit revision Super probably made in 1951
5G5 would be a brown tolex Pro made in 1959
6G5 would be a brown tolex Pro made after 1960
6G5-A would be a brown tolex Pro, made after 1960, second circuit revison.

[Kap'n]

Tube charts on 50's and 60's Fenders were often stamped with a two letter code that indicated the date of manufacture - year and month. The key being

First Letter
1951 = A
1952 = B
1953 = C
and so on.

Second Letter
January = A
February = B
etc.
I believe this practice started in 1953, however, curiously the code was created with 1951 being the first year of the code. So there aren't any amps with a code of "AG" for example.

This is not a hard and fast code. Greg Gagliano, in an article published in one of the vintage magazines, has documented examples where the factory didn't set the stamper properly. Because of this, it's important to use this as one part of the puzzle to date the amp.

[Kap'n]

Most US manufacturers of electronic components belonging to the Electronics Industry Association (EIA) stamped their components with a source-date code. These are usually found on speakers, transformers and potentiometers, but sometimes they can be used to date tubes as well.

The source-date code follows the following convention

two or three digits = manufacturer
hyphen (sometimes)
one or two digits = last digit(s) of year of manufacture
two digits = week of manufacture.

While this might seem somewhat confusing, a code containing anywhere from 5 to 7 digits, with a possible hypen, it's usually possible to identify whether it's a source-date code by looking at the first two or three digits.

For example, if you have a code on a speaker that starts with 220, it's probably a source date code, as 220 was the source code number for Jensen. Likewise 465 was the source code for Oxford.

137 was the code for CTS (Chicago Telephone Supply) often found on potentiometers.

606 was the code for Schumacher, who made transformers for nearly all of the blackface and silverface amp.

More Speaker Codes Here.

More Codes for electronic components here.

Example:

220523 would be a product made by Jensen in the 23rd week of 19_5

67-7736 would be an Eminence speaker made in the 36th week of 1977

606843 would be a Schumacher transformer made in the 43rd week of 19_8.

137354 would not be a source date code, as there is no 54th week.

As you can see, some cases you need to guess the decade, which can be often done by other clues. For example if it's an Alnico magnet Jensen, it's almost certainly from the 50's. If it's a ceramic magnet, it's almost certainly from the 60's or later. In general, most manufacturers seemed to have added the decade digit by the mid 70's.

Notes:

1. This code is only useful for dating if the component is original to the amp.
2. Components original to the amp must necessarily be built before the amp itself.
3. Fender did not often have large stocks of components on hand, the major exception being potentiometers in the mid/late 60's.
4. Obviously, JMI Voxes, Marshalls, Selmers, Stramps, Vamps, Watkins, Orange, Hiwatt, Univox, Teisco and other amps not made in the United States will not have EIA source-date codes, as they're not made with components made in the US.

[JAM]

Where's the 5F6 Bassman in the scale? I know it's an incomplete list, but the 5F6 has been considered by some to be one of Fenders best sounding amps.

[JAM]

...how similar in sound is a tweed (5E5, 5E7, 5F4) to the 5F6 Bassman? Seems with the different tone stack and long tail PI the Bassman is in class somewhere in between the Tweeds and BF Fenders

I thought about this last night. After putting down Teagle & Sprung's Fender Amps book, good as it is, it doesn't describe the different amp's character which is something frequently asked here.

How about it Lily & the Mods? Can we create a Tweed/BF/SF reference area that gives a brief description of each model's (and their variants) sound, volume etc?

TT

Yes, that's what I was wondering, I'm very familiar with the 5F6 Bassman sound as it was my main amp for several years. (I liked it better than my SFSR) I'd like that sound in a smaller (and lighter) package. The 5E7 looks ideal from that standpoint. From what I've read it's pretty close, but the 5E7 will breakup earlier and has more of a pronounced midrange.

I keep thinking of HR (Fezz will appreciate this). With the AD30VT I play a lot on the Bassman model (Tweed 4X10), and it reminds of HR saying "When people say they know what they like, they're actually saying they like what they know." In regards to this sound (of the Bassman) I like what I know.

[TT100]

There are models that are pretty familiar in the virtual sense to those of us who have never played them. What I mean is that amps like the tweed deluxe and champs have been discussed many times regarding their overdrive, clean tones, etc, but not so much has been discussed about tweed Bandmasters, Pros, Harvards, Tremolux or even the operation and response of the stand alone reverb units. And while not wanting to stray too far from the intended purpose by including FX like the reverb units, how about the Vibratone rotating speaker cab?

Back to the point, I'm hoping to have uncovered the mystery of which amps in the long Fender line actually overlap in terms of sound and character. Say, if I like a tweed Bassman sound but don't need the power or size what, if anything in the line, would come closest to the sound at lower power & smaller weight?

Some have very similar circuits like the tweed Super and tweed Pro but are pushing very different speakers. Also the BFVR and BFPro R. Very similar but different.

Anyway, the info provided already is a very good start!

TT

[Kap'n]

Where's the 5F6 Bassman in the scale? I know it's an incomplete list, but the 5F6 has been considered by some to be one of Fenders best sounding amps.

I'd put a 5F6 just before the BF/SF Super Reverb for clean, and between it and a twin for dirt.

[edit - while the 5F6 is a favored amp, the "holy-grail" version is generally accepted to be the 5F6-A. There are some small differences, IIRC, in the feedback loop, and the presence/absence of grid resistors]

You've also got to realize that I haven't necessarily played every single Fender amp, and some of it is conjecture going by general design, watts, and speakers. Somebody else could easily trump my rankings. Maybe I should just give them relative scale numbers, so it's easier to get full amp descriptions.

[JAM]

I think a cool addition to this would be the 'brown' Fenders 6Gxx series, I had a friends 6G6-B Bassman head here for a couple years- cool sounding amp.

[Kap'n]

There's a lot more amps to put on there. I'd probably also differentiate between 100W Twins, and 135W Twins, 45W and 70W Supers, Pros and Bassmans, etc.

[pc]

Again, I edited a lot of these posts (see first post in thread) to get more to the point. Kap'n, TT100, JAM, Fezz, feel free to edit them further or add new posts with more info. This is really a great thread for sheer info value.

[Kap'n]

What components look like...

Carbon Composition "Carbon Comp" Resistors. Some folks insist that these resistors sound better than other types. They're certainly noisier and more subject to value drift than others. Carbon comps were pretty much used through the seventies, but started to get phased out in the 80's by most manufacturers.

Metal Film and Carbon Film resistors. Sometimes referred to as "flameproof" these resistors are much closer tolerance than carbon comps and are used in most current "non-corksniffer" amps.

Cement resistors. Sometimes white, sometimes brown. Usually used for cathode biasing power tubes, these are higher power rating than any of the above resistors.

Wax capacitor. These pretty much disappeared by 1960 or so, and have a waxy outer coating, hence the name. These tend to get leaky after time. This photo is also an example of true 'point to point' wiring with 'spaghetti' on the wires.

Molded blue capacitor. These are found in brown and black face Fenders, and contribute to their sound.

"Orange Drop" capacitor. Made by Sprague/Vishay/SBE. Some of these sound better than others. This one is a series 716, which indicates polypropylene dielectric. Sometimes, but infrequently found stock in silver face Fenders. More often "Blue drop" and two different versions of "Chocolate drop" are found. The chocolate drops with yellow imprint are almost universally reviled.

Silver mica capacitor. Old Style. New Style. Used in tone circuits, usually.

Mustard caps. Usually found in Marshalls and Traynors, as well as others.

Electrolytic capacitor. Usually used as filter capacitors for power supplys, but also often used as cathode bypass capacitors in preamp circuits. They get old and dry out eventually and fail.. They also have polarity (arrow points to -). Hook them up correctly, or they will explode! Sometimes found in "Cans" like this.

[jerryjg]

Brilliant work Kap'n. Thanks for the time and effort. A much appreicated reference source!

[Kap'n]

1980 or so was the last year for silverface. 1981 had silverface amps with black faceplates. Late '81 or so brought the Rivera years. Twin Reverb II, etc.

In addition to the well known "silverface changes" that people talk about (grid 'tone sucker' caps, bias circuit, PI changes, pull boost, and eventually ultralinear output sections), there are other silverface changes. Later is worse for everything except grounding.

Cabinets
Cabinets transition from fingerjointed plywood with screwed in baffleboard to butt jointed plywood, to particle board.

Wire
Wire transitions from single strand, cloth covered push-back wire to multi-strand with really low melting-point plastic insulation. It's a real pain to work with, and probably at least partially responsible for the ugly lead dress of later SF amps.

Capacitors
Capacitors transition from blue molded 'tubular' caps to "brown drop" caps with yellow print to another sort of brown cap to "blue drop" caps. Some of the very late ('81 or so) amps may have come with orange drops. IMHO, the brown caps with yellow print are the worst sounding, and the blue tubular ones are the best.

Circuit boards
Later SF circuit boards are literally swimming in wax, and it's just aesthetically nasty.

Chassis
Ultralinear 70W and 135W amps have a funny chassis with three screws holding up the back of the chassis. Don't know if it's less structurally rigid, but it's a difference anyway.

Grounding
Somewhere around '72 or so, amps went from a two prong cord, and a two position ground switch to three prongs and a three position switch. Simply having the three prong plug does not make the amp safe. Only by having the switch in the middle position do you take the death cap out of the circuit. You're best off having somebody remove it entirely. Also note that if your amp is plugged in, the fuse holder is still "hot." Unless you rewire it, don't ever change your fuse while the amp is plugged in.

[boobtube21]

This was originally posted by Kap'n in another thread, but everytime I want to reference it I have a hard time remembering the thread name, plus I think it's a good addition here.

Power/wattages of various tweed/BF Fenders, *thanks Kap'n*:

...Model of amp, according to this chart:
1 = Champ: ~3 watts in tweed, 6 watts BF/SF
2 = Princeton: ~3 watts in tweed, 12 watts 6G2 and later
3 = Deluxe: 15 watts or so in tweed, 20 watts in tolex
4 = Super: 15-30 watts in tweed, ~40 watts in tolex
5 = Pro: similar to super
6 = Bassman: a bit more juice than super/pro/bandmaster
7 = Bandmaster: same as super/pro
8 = Twin: same power as bassman until the introduction of high power twin.
9 = Tremolux: ~10 watts tweed, 35w tolex
10 = Harvard: ~10 watts tweed
11 = Vibrolux: 15 watts tweed, 35w tolex
12 = Concert: tolex only, ~40W
13 = Vibrasonic: tolex only, ~45W
14 = Showman: tolex only, 80W
15 = Reverb unit: tolex only
16 = Vibroverb: tolex only, 35W

[ES350]

Just a minor note here--the 5E8A does not share the long tail PI of the 5F6A, it's an odd duck in-between the Super/Pro/Bandmaster design and the larger tweeds. A little less power and headroom when I compare my '56 Twin to my buddy's 5F6A.

[Kap'n]

A nomogram for choosing a cathode bypass cap.

(original, long-out-of-print source unknown)

"What's a nomogram?" you say. Easy, it's an analog calculator, like a slide rule, only easy to understand. You can use this tool to tweak the sound of your amp, and know what you're doing at the same time!

In this particular nomogram, if you know two of the following values

• the value of your cathode resistor
• the value of your cathode bypass capacitor
• the frequency of the rolloff desired

you can then draw a line between the two known points, and find the unknown value.

For example: On a typical Fender preamp circuit, you'll find a 1.5kohm cathode resistor and a 25uF bypass capacitor. Draw the line on the nomogram, and you'll find that the bass rolloff begins at 40 Hz (cps).

On a typical Marshall preamp, you'll find a 0.68uF capacitor and a 2.7kohm cathode resistor. The bass rolloff begins at around 400Hz. Your ear hears that as a mid boost and/or 'tightening up' of the bass frequencies.

[JAM]

How Vacuum Tubes Work

Basic but good information of vacuum tube operation.

[NTBluesGuitar]

Great article, JAM, I've read it many times before.

Thought it might be good to post something about bias? In response to a question about why the Hot Rod amps' bias reading is 68mV, and also includes some biasing math:

Well, your goal should not be getting a 68mV reading, as that measurement is the result of your bias setting. You want to be calculating what percentage of maximum plate dissipation your tubes are set at. You should be near 70% of max at the hottest.

The mV reading is the number you use to calculate that percentage.

With that said, here's the math:

Setting bias requires you have the 1ohm resistor from pins 8 to ground; that's labeled "Bias Test Point" on the HRD.

-Measure the reading at the 1ohm resistor before the ground; let's say 110mV DC
-Measure the plate voltage on the power tubes at pin 3 (careful...high voltage there!); let's say 385V DC
-Multiply cathode voltage by plate voltage. .110 x 385 = 42.35 (don't forget that 110mV = .110V). The resulting number is the total watts being dissipated.
-Divide the watts dissipated by 2 (since the HRD measures both power tubes at once). In this case 42.35 / 2 = 21.175 That's 21 Watts per tube.
-We know that 6L6GCs max plate dissipation is 30W, so divide the low number by the high number for the percentage of plate dissipation. In this case 21 / 30 = .677 or almost 68% maximum plate dissipation. Right where I want it for my tubes.

It seems complicated, but just focus on the reading at the 1ohm resistor and pin(s) 3. Write it down and practice the math a few times, and it's a cinch after getting used to it! I was really confused on all that for the longest time, but once it 'clicked' it was clear as day.

Also, think of this...let's say I was at 68mV at 385V (you know, like how that Fender factory bias number is so often referred to). If I were, it works out like this:

.068V x 385V = 26.18W, which is 13W per tube, 13W of 30W is 43%, which is 43% of max plate dissipation...pretty 'cold'. This illustrates why the cathode bias reading (mV number) needs the plate voltage to mean anything.

Tommy made me do it!

[Offshore Angler]

Just a quick note to clarify. In the description above last formula shows

.068V x 385V = 26.18W which is technically incorrect. It should read

.068A x 385V = 26.18W The reason the .068 is shown as V is that it is the voltage measured across a 1 Ohm resistor. The step that's missing is to realize that V=Amps/resistance. Since the resistance is 1 Ohm the Voltmeter reading will be the same value as Amps, but the formula as posted is incorrect in that while the value would be the same, the resulting units would be incorrect.

[Gris]

Hmmm, Kapn needs to redo his clean/dirty fender amp scale. My two fave Fender amps aren't even on there, LOL! (BF Bandmaster and tweed Bassman).

[marks sonics]

hi .i have a blues deville reissue with stock 5881 .i want to put a new set of sed 6l6gc in does the reissue have adjustable bias?.if not can these tubes be fitted to run correctly?what needs to be done? thanks