Vox AC4TV Mod Guide

Vox AC4TV Mod Guide

I have had my Vox AC15 for about 5 years now, and sometime last year I decided to get it a little brother: the Vox AC4TV. This tiny little 4w tube amp is incredible value for money. It only cost around $300 and is completely tube driven with 1 12AX7 preamp tube and 1 EL84 poweramp tube. It really is a tiny version of the AC15. From experience with the volume of the AC15 I also knew that 4w of tube power would be more than adequate for home practice as well, considering I would barely push the AC15 above 4w anyway when I’m practicing at home. This amp is very loud and is capable of great tone. It also has a very cool built in accentuator, this allows you to (at the simple turn of a knob) to change the amps output to either 1/2 a watt, 1w or the full 4w. It sounds legendary with my Fulltone OCD overdrive pedal, and the only thing the amp is missing is some reverb. Needless to say, the stock speaker is quite dull, but I still played on it for some time to allow it to break in. I was hoping that the speaker would open up and suprise me just as the stock AC15’s Wharefdale did (which I eventually swapped out for a Celestion Blue anyway). The speaker never sounded significantly different when it broke in compared to how it sounded stock. It sounded boxy (to be expected as it is a boxy amp I guess) and as though the tone was sinking in mud. I replaced the speaker with a Celestion G10 Greenback Speaker (10″) and it floored me with how much more articulate and open sounding it was. This was even before it broke in! Now the speaker has broken in nicely and it really does cut the cheese in the tone department. So much so that I’m even considering getting a cabinet for it, as I think once I do that it will be almost on par with my AC15!

This ends my Vox AC4TV modding adventure for now, the speaker change was absolutely necessary in my opinion as it really gave the amp character. Considering Vox now stock install Celestion G12M Greenback speakers in their new Vox AC15C1 amps, I don’t see why they don’t do the same thing for the AC4TVs. The only thing I would change with the amp now are the tubes, I would like to replace them with NOS, but I have some concerns:

  1. The tubes are installed on the circuit board which looks a bit dangerous to me, I don’t want to get electrocuted and die for the sake of changing tubes, and I also don’t want to fork out a wad of cash to my amp tech to do it.
  2. The tubes have no metal casing whatsoever, this could be a problem as the tubes might cook quickly and burn out, not really worth the NOS investment if this is the case.

If anyone has any suggestions for the above tube concerns please let me know, and also if anyone would like some further clarification please don’t hesitate to ask. I might upload some audio samples of before and after when I get around to it. Also be sure to check out my page on the Vox AC15 modding process!

This amp is an absolute steal at $249, if you want an all tube sound at a tiny size and price for your bedroom, don’t hesitate to pick one up today! I get a 4% commision from Amazon if you buy it from this link, so help a brother out and buy it from them if you decide you want one!

UPDATE 12/12/12:

I have done some more upgrades to the amp, for starters I replaced the stock Sovtek 12AX7 tube with a NOS Mullard 12AX7 and I replaced the stock Sovtek EL84 with a NOS Tesla EL84. This made an enormous difference to the tone of the amp. Second I purchased a matching extension cabinet (Vox V112TV) and fitted it with a Celestion G12M Greenback. The cabinet really opened up the sound of the AC4TV and now the 4W setting actually sounds almost as good as my AC15 with the Celestion Alnico Blue speaker. I’m still waiting for both of the Greenback speakers to break in, so it will only sound better in time! Considering both the AC4TV combo and matching cabinet are closed back the Greenback is undoubtedly the best speaker to put in these – Greenbacks are one of the few speakers that actually sound better in a closed back cabinet. In my opinion there is no good reason you should buy the cabinet + head when the combo is only a little bit cheaper than the head and yet can still be plugged into an external cabinet. Now I have a very impressive sounding amp for playing at home by myself or with others and if I ever need to I can unplug the combo from the cab and have an ultra portable amp to take with me anywhere I want. It really is an ultimate combination. Vox made a winner with this one. Once the Greenback breaks in I will record some audio samples allowing you to hear both the combo AC4TV by itself, and coupled with the 1×12 cabinet.

the 12" greenback
the 12″ Greenback
the stock speaker in the cabinet
the stock speaker in the cabinet
the Greenback screwed in the cabinet
the Greenback screwed in the cabinet
the 10" greenback in the ac4TV
the guts of the ac4TV
the guts of the ac4TV
close up of the NOS tubes
close up of the NOS tubes
close up of the controls
12AX7 on the left, EL84 on the right.
vox ac15

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48 responses to “Vox AC4TV Mod Guide”

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  2. sillyreverie Avatar

    Great job on the personal mod’s! Don’t let the techies have all the fun

  3. gregluhowymusic Avatar

    Excellent reckon. I’ve been wondering myself about the stock speaker as I know mine is nowhere near broken in. Sometimes I run it through a Supro 2X12 Cabinet with Vintage Jensens. Sounds lovely. Although I’m fairly certain the Jensens aren’t broken in either.

    1. caramellokoala Avatar

      Honestly, I found the stock speaker in this amp to be absolute rubbish… but then again I’m not running it through a cab, which would open up the sound a lot. Either way the stock amp didn’t improve much once it broke in. The Greenback I put in immediately out shined the stock speaker, and once it broke in it was obvious to any one’s ear. I have also played greenbacks through cabs and they are simply a super speaker! Jensens are great speakers as well, you’ll know when they’re broken in; one day you’ll plug your guitar in and the amp will sound completely different. Don’t rely on the stock AC4TV speaker on sounding any better than it already does, if you are unhappy with it now, I would change it.

      1. gregluhowymusic Avatar

        Thanks for that. A friend of mine questions the validity of a speakers’ need “to be broken in”. However He has never overdriven any of his amplifiers so I believe He would never have any way of knowing the bloody difference.

  4. caramellokoala Avatar

    Haha I have a few friends like that, they also believe that different speakers or tubes don’t have much effect on tone… the difference is definitely more noticeable with overdrive; I almost always play with overdrive, so I can appreciate a good broken in speaker as I’m sure you can! Thanks for your comments.

  5. Steve Avatar

    If you turn your amp on and let the tubes get warm then turn your amp off, the capacitors will discharge the energy in about 20 or 30 seconds but don’t turn your amp back on and unplug your amp when changing tubes. You can buy an insulated jumper wire for cheap at radio shack. Connect one clip to the chassi. Touch the other clip to the positive side of all the capacitors. That’s just a safety measure. You’re ready to change the tubes and you won’t get zapped. I like to wear rubber gloves when I touch the tubes. I feel they stay cleaner. JJ tubes work great in this amp and they wont break the bank.

    1. endofthegame Avatar

      Thanks for the advice, I’ll definitely keep that in mind when I change the tubes. I’ve heard a lot of positive things about JJ tubes, but I’ve tried them a couple of times and they’ve never delivered. One of the times they hissed badly and it sounded like I had a snake living in my amp! I prefer to buy NOS Tesla tubes, they were the company that JJ bought and took over, and the quality is much higher than it is now. I’m sure JJ tubes ‘can’ sound amazing, but they are in my experience too inconsistent to bother with. Tesla tubes are always good, and they’re only $30 a tube, which in my opinion is fair for a quality NOS EL84. As for 12AX7s, I would be even more likely to avoid JJ; there are way too many tubes that outclass them in that category, at a reasonable price too, eg: Tung Sol.

      1. MITCHELL E. STOKES Avatar

        I put a Ynug-Sol12AX7 in my AC4 and it made a huge difference. The Ruby tube it came with was not great. I am considering changing the EL 84 tube and wondered if I should use Tung-Sol or try another ??

  6. boob Avatar

    hello- thank you for the info! i was wondering why this amp sounded awesomer through my headphones.

  7. […] AC15 Mod Guide AC4TV Mod Guide […]

  8. Ted Anderson Avatar
    Ted Anderson

    Enlightening. Great site! Now – carry on . . .

  9. Robert Avatar

    Great info !

    Thanx for the info, cause i’m thinking to buy one myself 🙂
    Cheers from Holland.

  10. Mikaali Karlsson Avatar

    Great info! I have the AC4TV8 and i’m very happy with it.

    Question: when you connect a cabinet to the AC4TV combo, is the speaker inside the AC4TV still being used or is it turned off?

    1. endofthegame Avatar

      Cheers! When you connect to a cabinet the internal 10″ speaker in the combo is turned off.

  11. Manny Avatar

    Could you possibly explain how you switched the tubes out?

    1. pimpfreud Avatar

      Sure. I’m going to assume you’ve taken the control panel out and have the circuit board and tubes in front of you. If you look at the tubes they will have a metal wire coiled around their tip, simply take that off (wear surgical gloves whilst handling tubes) and yank the tube out. Underneath each tube will be a pattern of pins, and they connect into the circuit board into a pattern of holes, so they pop right out. To put the new ones in just align the pins with the holes and push them inside, twisting slightly to squeeze them in tightly. Then you just put the metal wire back over the tips and you’re done.

      1. AidenJ13 Avatar

        I know this is an old post but do you remember if you did anything safety wise so you wouldn’t get zapped? I swapped the tubes out of a blackstar ht1r combo once and didn’t even think about safety b/c I figured as long as I only touched the tubes I should be ok. Also, does anyone know if their a way to check if all the voltage has been discharged with a multimeter?

  12. Anders Avatar

    Good call on the speaker swap.. For lower powered british amps I would definately go greenback in the AC4 or the V112TV cab..

    I have that celestion 70/80 in a Laney LC50 amp,, which makes much more sense.. It is an 80 watt celestion speaker that works pretty well in a higher powered 50w open back amp.. It has a massive area of doping (the shiny material at the edge of the cone) which prevent is from cone cry when you drive it hard with distortion but also makes the speaker less articulate compared to a low wattage greenback with much less doping..
    And the greenbacks breakup character is a rock and roll staple…
    Also the heavy doping seem to take longer to get broken in.. My mate has a very used VOX labeled celestion which looks exactly like a 70/80 in his traynor YCV40 and mine sound very different in my Laney LC50 eventhough my amp has a very flexible clean channel..

    A dude on youtube compared a brand new greenback in a hardwired VOX AC15 with a speaker that had around 100 hours of play time (not loud gigging volume)… And the new speaker was more gritty and fizzy and the speaker with some use was bigger and rounder in the bottom with a less grating midrange and less fizzy with some top boost overdrive,,

  13. SwiftNick Avatar

    I’m glad I’m not the only one to take the AC4TV to a new level, really good thread! I did some mods last year are as follows:

    New 17″ x 15″ birch ply cab, stained gloss brown with Vox grille cloth, gold piping, Vox badge and leather handle.
    New 12″ Celestion Alnico Blue
    Harma Cryo 12AT7 and EL84 valves

    For me it’s the dogs bollocks and sounds crystal clear up to 12 o’clock then progressively breaks up with an amazing compressed overdrive. Sweet!

    1. Andrew Avatar

      Did u make the cab or buy it? I’m looking for a warmer less thin tone. The stock stuff is just weak. I’m will to get an entirely new cab if the wood really makes that much of a difference from the stock particle board.

  14. gregluhowymusic Avatar

    So what do you think made the most difference. The upgraded Valves or the Alnico Blue? I was very much tempted to do the same sort of modification.

  15. pxabrownAndrew Avatar

    where do you buy your tubes? I’m looking for a warmer, smoother sound then the stock speaker and tubes. I’ve got the head and matching cab. I’m also looking at a birch ply cab and putting my G12M Greenback in it. Did you get great tone with the wood from the stock cab?

  16. Emmanuel Avatar

    Hi there! Great post! I have a question on the combo being connected to the ext cabinet. When it’s connected, does the combo speaker cease to have sound? Or does the sound come from both the combo and the ext cab?


    1. Colin Avatar

      yes, it disconnects the internal speaker

  17. Colin Avatar

    I’ve had my AC4TV for about 4 years now, and always found it sounded a bit boxy, to the point I was looking to change it. But a friend gave me an empty, open back cabinet, which I put a 10″ Eminence in, and I replaced the stock 12ax7 with a JJ (after experimenting with Chinese, Sovtek and EHX) and the EL66 with a vintage valve from a 1961 Philips valve radio. This setup now sounds better than any Marshalls, Fenders and even AC15s that I put it up against – open, airy and so musical!

    Changing the valves is fairly low risk as you just unscrew all the screws around the plate on which the electrics are mounted (unclip the speaker for easier access), you can change the valves without putting your fingers near any components or cables).

  18. Oberst1 Avatar

    I can no longer find the ac4 extension cab any ideas?
    what about the Vox V212HWX Hand-Wired 2×12

    1. Mentzie Avatar

      Vox stopped the head and cab a while ago. Have a look at Thomann.de and their Harley Benton 1×12″ Vintage cab. I have their normal G112 which I’ve dropped a Celestion Seventy/80 in and my AC4TV10 sings its little head off through it. Nothing wrong with the stock HB speaker, which resembles a Seventy/80 in many ways, I just had a spare, run in one available.
      Mine has an Electro-Harmonix 12AY7 and JJ EL84 tubes, stock speaker ( very well run in indeed ) and in my opinion, the stock cab hampers it back to a fine sounding amp from an excellent amp when going back to running without a cab.
      Vox spec a 16ohm cab, but you’ll be fine with an 8ohm, just don’t use the attenuator or you risk burning the resistors out.
      The output transformer can handle 8ohms, but the attenuator can’t.

  19. Edson Avatar

    Hi, I bought a AC4TV combo recently, and I bought the “BitMod” which I’m currently waiting for. I have been considering to do the speaker change as you mention here. Is it possible, and would it make sense to try to switch with a 12″ Celestion Greenback instead? (In the combo, not an extension cabinet).


      1. Edson Avatar

        Thanks for the answer!

        Will the Celestion Greenback 10″ sound just as boxy as the stock one? Is it a no-brainer tonewise to do this switch? 🙂

  20. Joe Hartel Avatar
    Joe Hartel

    Where can I find the replacement tubes for this amplifier? Thanks!

  21. StratDude Avatar

    I have an AC4TVH (the head version) and I’m running it into an Egnater 1X12 Rebel cab, loaded with the stock Celestion Elite-80. The amp sounded a little boxy, even through the 12″ speaker. I did the C5 mod (replacing the capacitor with one of a higher value – google it) and it really opened up the bass of this amp. I did the Bitmo mod also which added a little versatility to it without affecting the tone. The thing to keep in mind is that this is a very unique-sounding amp. Some will love it, some will hate it (I happen to like it a lot), and it cannot be used in every application. But like any Vox, it certainly has its own tone. It will be difficult to make it sound like anything else, but on the other hand, you really wouldn’t want to.

  22. Nyles Avatar

    Before I purchase new tubes to replace the stock ones I know you said NOS Mullard 12ax7 and NOS Tesla EL84. Searching on ebay I found both available but I just want to make sure I buy the correct ones. Anything special I should know about either tube? The TESLA seemed pretty straight forward but the Mullard seemed like there were more options. Sorry for the stupid question. This is my first tube amp and I freaking love this thing. But I also love modding things. So any advice would be appreciated. Thanks! Great post BTW

    1. Michael Cunningham Avatar

      Yeah those tubes are the right ones, if you want to save some money get the NOS Tesla EL84s and some Tung Sol 12AX7s. Also be sure to replace the speaker as that makes the biggest difference with this amp!

      1. Nyles Avatar


  23. nyles Avatar

    Um so I bought the upgraded Celestion G10 GREENBACK speaker and it’s to large to even for inside the AC4TV. Has anyone else had this problem, I mean there is NO WAY I’m getting this thing in my AC4TV.

    1. nyles Avatar

      F*ck just realized there was an AC4TV8 DAMMIT. guess that’s what I have grrr… Any recommendations for a 8″ speaker? The current speaker is 6.5″ in diameter but I could fit an 8″ in there.

  24. Moe Avatar

    i’m a little late to the party, but the Greenback is THE mod to do with this thing. Playing with tubes with help as well. I think my favourite preamp tube in this thing was a NOS GE 12ax7. It really added some fatness and thick gain to the amp, and it paired really nicely with the Greenback. Cheers!

  25. Terry Last Avatar
    Terry Last

    My AC4tv has Weber blue pup 10″ (A$100) 8 Ohms with screen resistor added.
    Vox did a good “bundle” of impedance mismatch & valve selection to get a cool sound.
    The pup’s clean sound showed up my sloppy playing and it gave the “volume” (aka tone/overdrive) control another ten degrees of usable sweep.
    You are opening the load circuit and valves don’t like that.
    Power down, then change the attenuator. I made a 10 Watt ceramic resistor
    network that when added to the stock attenuator allows attenuation for an eight
    Ohm load operating at 8 – 10 Watts (double that of standard)
    If you have replaced the stock Vox speaker with an eight Ohm version then the
    attenuation resistor network may be drive beyond maximum power dissipation.

    The next biggest improvement was to put a “cat flap” in the back.
    I cut the rear panel and recycled the tenex (?) covering to make a
    hinged door. Some have posted a simple open rear but this allows
    both options and the change is worth the effort, without filth getting inside.
    (If I set the flap only 1 cm open there’s a sweet spot, bonus)
    The next time you have the rear panel removed
    (ACHTUNG assuming you are suitably qualified and experienced to safely
    work with LETHAL OPERATING VOLTAGES) try the open sound.

    I may add a series linear volume (aka tone etc) pot of 1/10
    the main pot resistance. This would allow 300 degrees of tone “tweeking”.
    A good amp but too crunched up and too retarded for volume/tone control.
    The times I hit a sweet setting with just a tweek and never be able to do it again.
    The triode/pentode switch is on the “to do” list.

    The AC15 is said to be the sweetest Vox. I’d like to build a single channel version.
    (No one uses the other channel and I could replace it with a Marshell channel.)
    Two 12″ green backs and all the headroom etc you’d want. (With a cat flap, of course)
    Last thought: My Vox has legs. Get the amp off the floor. It improves the sound and
    someone is less likely to put their foot through it.\

    Stay tuned Terry

  26. Jordan Avatar

    Thanks for this! About to do the same mod on my AC4TV. Chance you could send audio samples of before and after? Would love to hear the difference with the Greenback. Thanks again!

  27. Terry Last Avatar
    Terry Last

    My AC4TV was a shop demo amp at $300AUD.
    Vox cheated the specs to produce a fabo valve amp.
    The choice of “Ruby” 12AX7 and mismatched transformer
    driving a cheap sixteen Ohm speaker worked a treat, with trade-offs.
    The tone control is all within 20 degrees of arc on the VOLUME knob.
    (trade-off). The input amplitude has too much effect on the tone drive.
    My wah-wah (a Vox with no volume control) goes into boost
    when activated and drives the AC4TV into distortion, like it or not.
    (Bad Vox, naughty Vox, no battery)

    Mods I’ve used and recommend: ACHTUNG!

    1. Open the rear of the cab. My AC4TV has a cat flat.
    Cut slot across rear panel. Buy cheap hinge.
    Re-use Tolex covering and have a friction seal.
    This is the cheapest tone mod. Open the flap, close the flap.
    Test this by removing the rear panel screws and play
    the amp with the cab slightly open. ACHTUNG! DO NOT DIE!
    2. A weber 10″ Blue Pup ($100AUD) 8 Ohm speaker.
    Sounds so good I had to clean up my playing as the
    crummie original speaker’s (cool) dirty sound masked my
    You need to insert a screen resistor to maintain valve life.
    This requires cutting the circuit board and drilling tag holes.
    I suggest you use the the “External speaker” jack to find a
    16 Ohm speaker you like. The 16 Ohm speaker is standard
    spec so no circuit board mods required.
    3. If you do mod the board and use an 8 Ohm speaker, you
    can mod the attenuator with ceramic resistors to handle the
    extra output power. ACHTUNG! ALWAYS TURN OFF AC4TV
    When you change the attenuator, you actually disconnect the load
    (speaker) and valves don’t like driving no load. (Bad Vox .. etc)
    4. Get the amp off the floor. Mine’s got legs.
    I’m going to try the triode/pentode mod. It’s a simple switch, perhaps
    a switch The on the rear panel if “ordinary” or a foot-switch jack if cool (worthwhile). My AC4TV gigs with a PA mike.
    Next I’m saving for an AC15-C2. They say it was the sweetest and two
    12″ speakers = plenty volume. Cheers Terry

  28. Stratrat Avatar

    I feel that I owe this thread a comment because ( a year ago or so now) I used it as a reference. Basically (and I’m no tech) upgraded the valves to Mullards and swapped out the speaker for a 10″ Greenback. Well, I did try playing it through a Vox 1 x 12″ (Greenback) cabinet for a while but I actually prefer the sound of the 10″ in the combo. In my opinion, the valve and speaker mod is all you need to do to make a good little amp a great one!

    1. JR Avatar

      Good to hear! Just curious, what made you decide Greenback and not Gold or G10 Vintage?


      1. Stratrat Avatar

        Sorry about the slow reply. Went for the Greenback because that seemed the universally-recommended replacement (and a good fit for dirt, over-driven blues).

    2. JR Avatar

      Also, did you open up the back at all, as some above have demonstrated?

      1. Stratrat Avatar

        Thought about it but haven’t felt the need. I typically play on the 1 watt setting – either without any pedal but reverb at 7/10 volume or higher (where the sound quality becomes BIG) – or at lower volumes with various distortion/overdrive/boost pedals. Occasionally plug into a 1×12 Greenback cabinet I have but seldom feel the need – the 10″ Greenback lives up to its reputation as “the 10 that thinks it’s a 12”.

  29. EG Avatar

    Hi, is the G10 Greenback a direct swap for the VX10 in an AC4TV? I am thinking of going down that route and just curious about the actual fit in the combo enclosure. Hope to hear back, thanks.

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