Vox AC15 modification ECC83 EF86 input stage
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- Опубликовано: 4 июн 2022
- Is there a difference between an triode ECC83 or a pentode EF86 as input tube. Guitar amplifiers used the EF86 mid 1960’s. After that came the triode ECC83. Nowadays people prefer the earlier EF86. Why? The pentode EF86 is noisy, very microphonic and sensible for hum. Mostly because of its enormous amplification, not at all necessary in a guitar amplifier. Then why do people want them. Because of the story’s on internet, the meaning of another guitarist? It’s strange. Is there a difference in sound as some people claim? My brother-in-law is one of those people. I hesitated to do the modification. What in .. name is so different? I investigated.
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Just when I was about to comment that a guitar signal isn’t just one frequency, you got to the point about harmonics and showed the differences in on the scope. Nice experiment, and I like that mounting idea.
The designer of the AC15, Dick Denney, was also a guitarist. He preferred the EF86 precisely because of the harmonics.
I love the EF86 channel in my Matchless SC30 clone, there are very real tonal differences when the preamp is driven.
I have a Vox AC30, 1997 Marshall built in the UK with an EF86 preamp add-on which simulates the sound of an original AC15 and the AC30/4, which is EF86 driven also. I was brought up on the sound of the UK Shadows group in the 1960s and to my mind the EF86s were far better than their successor, the ECC83 driven AC30 top boost. There is a world of difference between the two circuits in terms of tone. Hank Marvin, lead guitar with the Shadows, had complaints about the deterioration in tone when he switched to the AC30 Top Boost - and with good reason. The Ef86 gives a smoother and more rounded tone with a creamy top end which is not rivalled in any way by the ECC83. The latter has a significantly harsher and more "clipped" treble tone. I have installed an original Mullard NOS valve/tube in the "AC15" preamp . This is exactly what Mr. Marvin had in his original Vox amps and what a tone it produces, blowing away the ECC83 sound. Your relative is right to ask you to make this modification. It will produce those sounds from the early 1960s unobtainable with the later ECC83s.
I have the 50th I dig it:)
Thank You, this was wonderfully done and very informative.
Ik moet nodig bij je zwager langs
Ik heb uitvoerig contact met hennie gehad over de ef86 kanaal om eens bij hem te luisteren ik ben ook Shadows fanaat ik heb al de goodman speakers uit 1963 in mijn ac15
Dus ik ben benieuwd je zwager was razend enthousiast over de ef86
Mvg
Mannes
I am sorry; but i never stated that the input tube is overloaded. You are right, that if you put a echo unit in front of the amplifier, it is possible to overload the input tube IF you open the input control to far. But that was not the case. I only wanted to investigate, about all those story's around differences in using a ECC or EF input tube. And yes there are. See the end of the film. It’s the balance between the ground wave and it’s harmonics. They are handled different by the ECC and EF.
BUT DO NOT FORGET, also the surrounding resistors and capacitors play an important role. And hopefully nowhere is the sound ‘clipt’ by overloading a tube, because that will give a total other sound then. Measurement are done with a non-clipt sinus and harmonics. (a pure sinus has no harmonics, a guitar sound has many !)
"I fear part of the choice for an amplifier is made on feeling and intuition". Modification is made very well by not mounting EF86 to the chasis, this way new and some NOS tubes can be used despite supposed horrible noise, microphonics and all the bad things they do :) Joke aside, i love EF86 in pro audio input stages, also guitar stuff with nice flexible mounting as we see here. You might like EH EF86 which is several times cheaper than Telefunken and very consistent, i use them all the time but only found a few out of specifications like noise and ele. parameters.
I've got an EF86 preamp in an amp I built. It's a vox type thing with switchable coupling caps and two el84s in push pull. It's a head. I don't think I'd try to build a combo with one. I guess I've been Lucky, with only rubber rings for dampers I've never had any trouble out of three different EF86s. They aren't anything special and one is a very cheap Chinese thing. The one I run is an ef806 I can't remember it might be electro harmonix? Anyway it sounds great and hearing the horror stories from everyone about them I always treat them carefully. I don't know, it doesn't get used regularly I just fire it up every once in awhile but never had any trouble. Knock on Wood
@@lauratanner8475 Good to hear about Vox type amp, 6V6 sound really good in place of EL84. Having Vox front end and output transformer would make it sound pretty much like Vox with added bonus from 6V6. i recall seeing noval version of it with a little lower plate dissipation, both western and eastern NOS.
EH is calling them EF86, i see this as serious approach to making tubes. No new production tube is up to spec for being special quality like EF806, 5751, E88CC, etc. Most of this were 10.000 hour low noise tubes, some of them capable of functioning in the mic right out of the box (very demanding application).
EF86's got bad reputation because people use them in a wrong way or don't care to use them properly. Old datasheets are very clear about flexible mounting where is needed, having it in head with o rings is normally enough, they also work in combos but require a bit of work to make flexible mounting. I find Svetlana/Winged C very non microphonic, EH is good at this too, the rest like NOS depends on what you find as some are better than others. Do you run it at high gain having 150-200k anode resistor? Lowering gain helps further while retaining drive and sound.
@@Signal_Glow I've got a 100 k for the plate but I don't remember the plate voltage right now I'd have to look at my notes. I do remember tinkering with values around it for quite awhile until I was happy with it. It's a ton of gain even with the lower plate load resistor. I also use a bit of negative feedback in that amp to tame it down a little more. I can't remember specific values and voltages off the top of my head tho. Oh yea that's me under the Laura tanner account above, my girlfriend's account lol. In case of confusion.
@@michaelknight4041 One idea; making 6SN7 splitter and 6V6 output, sounds great with very few higher order distortion. Great for everything except metal.
I did watch twice your video. I don't understand if you mean that a guitar plugged straight into an ac15 will cause the tube to clip. As i understand v1, the channel volume control is right after it and its the phase inverter that clips when the master volume is set low and the channel volume is maxed, not the first tube. In the case of the shadows music, Hank marvin did use a meazzi echo before his amplifier, maybe this lightly overdrives the first tube.
I am sorry; but i never stated that the input tube is overloaded. You are right, that if you put a echo unit in front of the amplifier, it is possible to overload the input tube IF you open the input control to far. But that was not the case. I only wanted to investigate, about all those story's around differences in using a ECC or EF input tube. And yes there are. See the end of the film. It’s the balance between the ground wave and it’s harmonics. They are handled different by the ECC and EF.
BUT DO NOT FORGET, also the surrounding resistors and capacitors play an important role. And hopefully nowhere is the sound ‘clipt’ by overloading a tube, because that will give a total other sound then. Measurement are done with a non-clipt sinus and harmonics. (a pure sinus has no harmonics, a guitar sound has many !)
@@TheoFaber thank you for all the clarifications, I was trying to find a way to bias differently the first 12ax7 in my ac15c1 to behave more like a ef86.It seams there is no way around to sound more like the ef86.The one think i found was that a 100k plate resistor has more headroom than a 220k; also, i tried limiting the boost of booth signal in the op-amps.I bypass the 820k feedback resistor of U1 with 2M.Booth channel are getting a clean boost in the op-amp circuit in the stock form.To my calculation, by doing this modification, the top boost channel gets exactly the gain of pure valve vox.The normal channel is still 1.7x ( it is near 55% of what it is stock) the gain of the normal channel of an ac30 that use a 12ax7 with a 220k plate resistor, a 500k volume pot and a 220k in line before the phase inverter.The difference is that the volume control is right before the op-amps in the normal channel ; there is nothing in the top boost channel at this place in the curcuit, so its more important to get that one right cause of its fixed nature.
@@Desaulnierspf Altering (anode) values of the resistor(s) alters indeed the amplification. Because the internal resistance of the tube, has a certain value, if the cathode stays fully decoupled. So the tube is no longer optimal terminated. I do not have the info of different Vox amps.
I only know, that all the discussions are around the amp’s ‘sounds like…..’ ??? Yes; I am a technician!!! If you want to duplicate the sound / design of VOX, you must use there value’s. And they are using 220K as anode resistor of the EF86 (NOT THE ECC). If you want less amplification in that first stage, you have to do something about the de-coupling of the cathode.
As stated in the film, Vox made a series of amps that imitate a pentode / triode, by simply connecting some grids.
It all comes down to; what are you trying to accomplish. Improve on VOX design? or simply sound like a VOX… As technician; some-times I do not understand all the fuss …… hi! What I have proved, is that indeed there is a difference in sound between a ECC triode and a EF86. Even I did not believed it, when I started….
@@TheoFaber you sure proved it the audio waves shows it.Please post a video of some shadows playing on this amp ; it would be nice to hear the difference between the two tubes on the same song.
@@Desaulnierspf Sorry for the delay, but the music thats in de film, are not the Shadows and I do not have a recoding. You have to look els ware, i only have the comparison of test signals and thats in the film.
Henny zou nog een poos geleden een demo laten horen en zeggen wat het eventueel zou kosten zo'n EF86 kanaal maar hoor niks meer van hem
Dus ik vraag het u zelf maar ik heb een Vox ac15 twin en zou ook de ef86 kanaal willen
Ik zie ook dat u radio zendamateur bent
Ik toevallig ook PD3MCF
Beste; Je moet Hennie maar rechtstreeks vragen om een demo, ik weet eigenlijk van niets. Het modificeren van een Vox met een extra EF kanaal is buitensporig duur, dus zou dat afraden. Ts gewoon heel veel werk, wil je het netjes doen. Leuk een mede zendamateur, hoewel ik zeer zelden iets uitzend...hi... groet en dus 73 van PA2THF (Theo).
There is a definite sound difference in the EF86 compared to the 12AX7 (ECC83) The EF86 is louder and has a grit to it and more character, much more than an ECC83. There is a mod to the VOX that adds the EF86 preamp to it. Many people use this. Here is a video on the sound difference, NOT a Vox but EF86 vs 12AX7 Check out this video ruclips.net/video/k6Z5au_mfb8/видео.html