Just a tube question

Hi all,

I've only just had the thought of trying out some of the tubes I have lying around on my Orange AD15.

The amp uses 2 ECC83s, and I have the following within the same family :

• 2 12AX7s (same thing if I'm not mistaken) -- Brimar and Miniwatt/Dario
• 2 12AU7/ECC82s -- Miniwatt/Dario
• 1 ECC81 (=12AT7) -- Miniwatt/Dario
• 1 EC86 -- Mazda

My question must be very basic, but I just don't know enough about these things!

If I want to switch some around, which ones may I use or not use, and in what order? Must I use 2 identical tubes at all times?

everything but the ec86 is interchangeable, which if I recall is a single high mu small signal triode whereas the others are dual triodes with hum cancelling and shared heaters, yada yada, you probably don't care....

the 83s/ax7s have a gain in voltage of 100, the 82s/au7s have a really low gain and a very linear reponse to boot that is generally not great for guitar amps unless its in a cathodyne phase inverter or an amp that needs expanded headroom because it has a lot of potential gain on the clean channel like a vox... and the AT7/81? that has a gain of 70 to 80, but unlike the similar 12AY7 and the lower gain AX7 variants Leo Fender was so fond of that perform identically to an AX7/83 apart from the lowered gain in voltage, the AT7/81 also has a very low output impedance into the next stage so for any stage that doesn't directly preceed a cathode follower (an impedance lowering tube stage generally used to feed tone sections to minimize loss of gain in treble due to the loading of the tone stack on a high impedance preamp signal like in tweed fenders and marshalls) you will get a change in the frequency response and slew rate as you start to enter distortion territory changing from an ax7 to an at7.... fender and hiwatt also favored them as long-tailed pair phase inverters and any amp with a long-tailed pair (most modern push-pull designs including the AD15) can swap between these 2 tubes in the phase inverter slot for a change in output stage response

in 12ax7/ecc83 types the Dario's aren't bad while mazdas and brimars are great, like almost 50s Mullard great... I quite like Mullard's ecc81s and notoriously swap them for V1 in amps that I think have a little too much preamp gain and upper midrange fizz but I've never used the Dario version... you au7 is worth a try in ANY position in your amp, but it probably won't pelase you, its more of a hifi triode which is why its rare to see it specified for gain applications in guitar designs, they are mainly used in non-gain producing phase inverter types and as trem/vibrato oscillators

I always have some brimar, mazda and Mullard 83s and 81s (especially the military grade ones with the CV designation, wow are they good) around because I am quite fond of them in V1 of vox/marshall/orange type circuits followed by a current production tung sol 12ax7 in V2... I also have some backup mazda and Dario ef86 pentodes in case the Mullard ef86 in the matchless goes bad on the job

my other favorite 12ax7 types are GE grey plates, ANY RCA ax7 (their at7 is best left to phase inverter duties) and the mighty amperex bugle boys that were made in holland which are becoming so hard to come by

in your amp the most suitable position to experiment with tube type substitutions is V1

so to sum up: don't use the ec86 because it will likely fry something in your amp, but DO mix and match any other tubes from your collection in any slot. As a rule of thumb the ecc82 is probably not suited to your amp since the AD15 isn't a gain monster that can benefit from a couple stages with less gain and more dynamics... although putting it in the phase inverter position which is probably V2 in your amp may yield a more dynamic, clean and 'hiwatt' like power amp feel with reduced volume and no distortion in the first 2/3rd of the master volume, but you may find it to be anemic at anything less than ear-splitting levels

dedicate some serious time to auditioning tubes at various volume and tone settings with all your guitars and effects and make notes, then go back a few days later and do it again.... if your notes on what sounds good where are the same both times you have a winning peamp tube compliment

also, make sure to listen for microphonic rings and squeals at volume, the euro tubes were more prone to this than USA tubes were... microphonic tubes ALWAYS get worse with time, so you should discard any tubes with audible ringing... if you're unsure what noises are coming from the tube versus your signal chain then unplug everything, crank the amp and tap the tubes very gently with a rubber eraser. You should hear a thud, but it shouldn't sustain r become a ringing sound or feedback.

these are all quality old tubes but aren't used in many if any guitar amps...

EDIT (long, boring version, read at your own risk): the 801 may be an at7 with a german designation, they love adding zeroes for some reason... the phillips 86 may be a disguised Telefunken or Mullard ef86 (aka ef806) an excellent small signal pentode for hifi, broadcast and pro audio that was also used by vox, selmer and later matchless and their copycats but is not interchangeable without modding in any other amplifier. They tend to be mcirophonic and are very susceptible to squealing in combos so dampers are needed. I find the mesh and solid shield Mullards to be the best for guitar amps and use a mesh in my matchless with an EAT cool damper because even in a head if you put it on the cabinet it can vibrate squeals from the tube. The rest of the stuff has me scratching my head. For pro audio I use the telefunkens or 70s/80s pre-JJ Tesla EF806es. Who knows what you have, DW is not usually a signal tube prefix in my experience.

The most common guitar preamp tube european designations will be ECC81, 82 and 83, these are just 12au7, 12at7 and 12ax7es respectively but europe made theirs with different materials, bottle, plate and filament structures so they all sound different..... lesser used are the pentodes, most common guitar pentode is the mighty EF86 followed by the american 6SJ7 sharp cutoff pentode and the 5879 mini. All of these dual triodes and small signal pentodes or variations thereof are also used in pro audio gear and hifi. The 86 pentode, 81 and 82 dual triodes and variations of those triodes in single triode format are very common in condenser microphone designs from germany. You find the 6SJ7 in a lot of limiting amplifiers and varimu compressors but I don't know its euro designation off the top of my head. The 5879 has a low in common with the EF86, as far as I know the designation is a NATO number and is the same on both continents.... the 5879 s in some US recording gear and is in a number of gibson designs from the end of the tweed era replacing the octal base 6SJ7 when everyone went over to minis. Vintage ampegs with the hard to find 7199 triode/pentode as the cathodyne PI and driver can be modded for another socket to use half and 82 and an ef86 or 5879 as the driver stage before it since the 99 is basically those 2 tubes in one bottle. Although there are other similar single bottle triode/pentode workarounds too like the 6U8 if you have a V series amp. I digress.

I would have to look up all these tubes and see what their US designations are to tell you what they're actually meant for, but its probably not guitar amps and maybe not even audio. A lot of tubes were made for radio frequencies or TV use. Some can be repurposed for music use with a careful design, but generally not, RF and TV tubes are too prone to squealing at the top of the audio range when exposed to even the tiniest mechnaical vibration... this tendency wasn't a problem in video reproduction and could beignored in broadcast assuming the thing wasn't in the AM amplifier circuit.

in your amp you should probably just use a 12ax7 aka ecc83, put a good current production tube in there, nothing chinese.... it probably needs all that gain to get its sound since its mostly digital and one stage does a V1 input stage and the other is producing modest dirt somewhere in the modelling section before the solid state power amp. You could try a 12at7 aka ecc81, I would not bother with a 12au7 aka ecc82 very low gain and linear The AT7 also has a different output impedance than the other 12__7 tubes so it'll change the reponse of those stages in a tube amp, although in this weird hybrid monstrosity who knows what kidna input impedance there is between stages. I would think that the impedance into the AD converters is so high the output impedance of the tube stages will have a negligible effect if any. There's also the 12ay7 and the 12dw7 that's half 12ax7, half 12au7 but I don't think those have a euro equivalent or I don't know what they are. Anything that's not a dual triode with the correct pin out will fry the thing. If you need headroom try an AT7 or AY7 maybe... although it could be the solid state power amplifier too, at that price point who knows what you get.