B+ 300V, Ra 220k and something like Ua 150V. So pretty much like the std EF86 workingpoint. And go for cathode-bias on the upper half with unbypassed cathode resistor. Seems weired with that low current, but it works!
Anatoliy,
Have you ever tried the triodehalf(u=+100, S=19) of the 6F12P as input device in a guitar amp.
Wow, not even one control on the amp. no gain, tone or master volume. I must be for the player who likes to use the knobs on the guitar. Actuly that would be ideal if it could work like that, you'd tweek the amp by adjusting component values and then fine tune using the tone and volume controls on the guitar body. They call amps "touch sensitive" it you can control the tone just be digging in a bit with the pick. But an amp that finely tuned can NOT be built be following a schematic. it will need to be tweaked using the you own guitar because guitars differ so much.
That is one advantage of building a clone of a mass produced, well known amp. These amps have a wide range of tone you control with gain, tone and MV.
Some examples of amp voicing: As I type this there's an amp to my left I'm finishing. I like the tone on the first two strings (high E and B) but as I turn up the gain the rattle type sound happens to quickly on the 3rd open string, so as I play an open G then a B above it the tone changes, a lot. If I turn the gain down the entire amp cleans up and the bass gets stronger. How to fix the tone-change problem? I'll by swapping a 1uF cathode bypass cap on the third triode to a 4.7uF and see what happens after a few hours of playing before and after the mod. Then I'll see about changing the bias point on the first triode, I think it's slightly "cold". I think maybe more clean headroom in that stage might be best. Over all the amp plays well and goes from clean to crunch. Only the transition to crunch is uneven on all the strings if using a Stratocaster. I wrote all that just to point out the fun you get to have if you go off the well tested path. I think it's worth it but just do NOT expect to be finished after the last part is soldered. Only after several weeks of use will you know it you are "done".
One bit of practical advice: Do not NOT wrap the component leads around the tags before you solder as it is nearly impossible to unsolder without clipping leads. I like using turrets or eyelets so I can unsolder the parts many times. Turret boards are also nearly indestructible and look neat too. I place component leads inside the hollow turrets and wiring wrapped around the outside, allows for easy mods.
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jjman said:
By "jazz amps" do you mean something like a Polytone Mini-Brute? If so, I hear ya, man... I'm not a fan of the "pillow tone."
Well, it's best to take into account that there are those who want a loud, clean and uncolored ("hifi") sounding amplifier to play through, while there are others for whom the amp is as much a part of the instrument's color or tone quality as the guitar/pickup combination.
I mean, how does one define what a "jazz guitar" is? Even among (non-rock or fusion) "straight ahead" jazz players, there is a wide variety of guitar types chosen.
Usually you think of the Gibson L5CES or ES-175 as the normal type of "jazz guitar." You know, the hollow-body archtop with f-holes and humbucking pickups as played by Wes Montgomery, Jim Hall, Kenny Burrell, Herb Ellis, Joe Pass, and so on. However...
Ed Bickert plays a Fender Telecaster, which was pretty much stock on the Paul Desmond album "Pure Desmond" -- complete with little, single-coil neck position pickup. Is a stock Telecaster a "jazz guitar"? It is for Ed Bickert! Wait a minute, you say, "I thought a Tele was a 'country' guitar..."
Grant Green played a Gibson ES-330 (two single-coil pickups on a hollow ES-335 style body) on some of the Blue Note records he made in the mid-'60s. That's the same type guitar as the Beatles were using around the time of Sgt Pepper's.
So it is with amplifiers. I'll bet there's somebody out there playing an ES-175 through a Marshall combo amp and getting a great tone.
On the other hand, there are some fingerstyle guitarists who favor a very "hifi" sound, with something like a Bartolini pickup on an acoustic archtop guitar, played through something like a Walter Woods amp (a portable, solid-state PA head with a clean sound). That's kind of in the ballpark of the "acoustic guitar amp" setups for flat-top guitars with piezo (or similar) pickups.
FWIW, I find there's something very satisfying about a good ol' Gibson PAF on a decent archtop (that sounds good acoustically) played through a black- or silverface Fender open-back combo amp in good condition, with classic Jensen C12N or similar speakers.
Don't forget that the speaker and speaker cabinet have an awful lot to do with the final "tone"!
Oh yeah... After the basics are taken care of, a lot of the sound is in your hands. I remember a gig I played where a certain famous jazz guitarist (who I practically idolize) asked if he could use my setup to sit in. I said sure. This certain guitarist with a very distinctive, unique sound, played my guitar and amp and sounded absolutely like himself -- and nothing like me! (Fortunately for him!!)
In the end, you do whatever you have to do to get the sound you hear in your head out into the air. An awful lot of it is in your ears and in your hands. But a nice, warm sounding tube amp sure does help!
-=|=-
PS - a nice, simple tube amp with nothing more than a volume control might be a good thing. I wanted to try that at one point...
+1
+/10: it depends on style, and on guitar used for the style. I meant a classic Jazz - guitar, large hollow-body with acoustic resonators, he meant just a peace of wood with pickups that really requires something like amps or pedals to sound less boring.
I wrote "Marshall combo amp" not "Marshall stack." Marshall makes some small ones with 1-12", etc. Too much gain for my taste, but they could be used.
Also, the main reason for small combo amps is that you don't need any more sound in a jazz group than you can get with about 30 to 50 watts into a small 1-12" cabinet, and jazz gigs don't pay much, so why carry a ton of gear? If it's a quiet group then you could certainly get away with 15 to 20 watts into that 12".
I once saw Joshua Redman at the Village Vanguard with Pat Metheny on guitar (and Charlie Haden on acoustic bass, Billy Higgins on drums). Pat sat between two large speaker cabinets with this enormous rack of electronics with blinking lights and all sorts of crazy stuff. I have no idea what was going on in there, but it was an enormous setup for a place as small as the Vanguard. But as usual, Pat sounded just like Pat Metheny.
-=|=-
Ah, unless you're Ed Bickert with a Telecaster!
http://www.amazon.com/gp/product/B004I5WW6S/ref=pd_lpo_k2_dp_sr_1?pf_rd_p=486539851
Amazon.com: At the Garden Party: Don Thompson Ed Bickert: MP3 Downloads
http://www.amazon.com/Out-of-the-Past/dp/B0015R62FO/ref=sr_shvl_album_1?ie=UTF8&qid=1307988076
http://www.amazon.com/Out-of-the-Past/dp/B0015R62FO/ref=pd_sim_dmusic_a_1#mp3TrackPlayer
...And if you've never heard him, Bickert is really one of the great ones in the classic "straight ahead" style. Beautiful sound, lovely melodic sense, lush harmonic sense, swingin', the whole package. If you like Jim Hall's playing then you'll really appreciate Ed Bickert.
-=|=-
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A JCM600 1X12 will do it!
Also a Messa Boogie 1X12 also good!
Or something with lots of 2nd Harmonic and Les Paul on the guitar..LOL
Regards
M. Gregg
You mean something like this then? I built this for my niece, she plays acoustic. EL34 PP with 6GK5 input stage and 12AU7 phase splitter.
Attachments
Yeah, that is cute! I'll bet it sounds nice too. The 6GK5 is the input tube? Nice. High impedance enough for a piezo (or similar) pickup straight in? Have you ever tried the amp with a standard electric guitar? If so, how did that sound?
I was actually thinking that any Fender "Normal" channel circuit would work without its tone controls. You see, I was playing around in Duncan Amps' Tone Stack Calculator (TSC). TSC predicted that for flat(-ish) response from the Fender blackface tone stack, the Bass control should be set at about 3, while the Treble control is set at about 1, and the Mid control set to about 7 (or 6.8k ohms, which is the value chosen for amps that don't have a Mid control). I never use the Bright switch (250pF from top to wiper of Vol pot).
I tried those settings and found them to work very well with my old Gibson Howard Roberts with PAF humbucker. I use the Tone control on the guitar to control the brightness, and keep the Volume control at between 5 and 9 (it gets too bright at 10). It might just be that I don't need anything more than a Vol control on the amp, or at most a Tone control (hi-cut only). Couple that with a Jensen C12N and you'd have a nice little "vintage" sounding combo, I'd think.
-=|=-
Funny you should mention the Ampeg Jet. That's another really fine sounding 20 watt/1-12" speaker combo. I had one, but sold it (and I shouldn't have!). That would work great with a Howard Roberts or similar guitar (L5CES, ES-175, Guild X-500, Ibanez Joe Pass, etc.).
Is my gear mania showing?
It sounds good with electric guitar, its basically a mono hifi amp with a bit more gain. It surprised me that I don't miss the tone controls. It just works, just like a hifi amp does with no tone controls. Topology is input>6GK5>vol control>12AU7 gain>12AU7 cathodyne>EL34 PP. There's a short thread on it somewhere here. Maybe it would make a good jazz amp. At first I had a 12AT7 instead of the 12AU7 and that gave it some really sweet non-linear characteristics when driven
It sounds good with electric guitar, its basically a mono hifi amp with a bit more gain. It surprised me that I don't miss the tone controls. It just works, just like a hifi amp does with no tone controls. Topology is input>6GK5>vol control>12AU7 gain>12AU7 cathodyne>EL34 PP. There's a short thread on it somewhere here. Maybe it would make a good jazz amp. At first I had a 12AT7 instead of the 12AU7 and that gave it some really sweet non-linear characteristics when driven
Did you use global negative feedback around the OPT, EL34's, 12AU7? If so, about how much?
I like the idea of a high gm tube at the input. I'll bet that would make for a more "interesting" clean sound. (More "detail"?)
I've tried modding a Fender blackface-style amp to use a 12AU7 as the Schmitt inverter, but I found it made the amp sound too "dry." The stock 12AT7 was a good choice tone-wise. I find a 12AX7 there (like in a tweed Fender or Marshall) sounds too wet and mushy, but makes a nice overdriven tone.
The fun part of a guitar amp is that it's as much a tone-generating machine as it is an amplifier.
No feedback, its very linear as is, no need. There is local feedback since there are no cathode bypass caps.
I really like 12AT7 as a phase inverter, definitely. Very smooth gentle breakup. Works great in both hifi and guitar, now that's unusual! (Except for hifi you don't let it break up...)
schematic
I really like 12AT7 as a phase inverter, definitely. Very smooth gentle breakup. Works great in both hifi and guitar, now that's unusual! (Except for hifi you don't let it break up...)
schematic
In the '60s a lot of the NY studio cats used Ampeg Gemini II amps. They had a club, each member bought a Gemini and planted it at one studio; any member of the club doing a session at that studio could use the amp. They had a key to operate the on-off switch on each amp to keep unauthorized players from using them. So there were identical Ampeg Gemini amps at every major studio in NY. A lot of jazz tracks and film scores would have been cut with those amps, as well as pop singles.
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