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Ac30 transformer swap ( don't want to kill myself lol)

Discussion in 'Amps and Cabs' started by blasius01, May 17, 2011.

  1. blasius01

    blasius01 Member

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    So I just bought mercury magnetic power and output transformer + a choke. Has anyone done this yet on a vox??? How long do you need to leave the amp unplugged to discharge it??? I know a decent amount about wiring but I want to make sure I'm safe and live to hear the difference ;) a amp repair guy in town said it would cost around 200 for them to do. Since I already spent 500 on the stuff I really don't want to spend more

    Any help is appreciated :)
     
  2. xray

    xray Gold Supporting Member

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    Take it to a pro my friend. Don't risk your health on an amp. I don't care how much you know about wiring.
     
    Last edited: May 17, 2011
  3. 6AM

    6AM Member

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    The easiest way to discharge your caps is to play the amp and while playing it, unplug it while continuing to play (just hit a lot of low open E). You'll hear the caps draining as the volume fades. Keep hitting strings for about 30 seconds and you should be fine.
     
  4. blasius01

    blasius01 Member

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    Wow i never heard that
     
  5. blasius01

    blasius01 Member

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    Wow i never heard that
     
  6. zzmoore

    zzmoore Member

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    Is this for a CC.?
    The choke CAN be real hard to access for securing, especially if it does not "drop" right in.
    The PT and OT have a lot of wires that are very important.
    My advice.......return the PT and the choke, you do not need them. (are yours burned up.?)
    Install the OT and see what you think. Don't lie to your self. If you cannot hear/feel a difference with the new OT, do not worry. It is not a crime. You can always sell the OT used and recoup most of your dough.
    If you lived near me I would give you a hand.
    Good Luck
     
  7. Lemmings

    Lemmings Member

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    Not to be rude, but if you don't know some of the fundamental stuff like discharging capacitors it's probably not the best idea to be doing your own amp mods just yet. There be deadly electricity inside those things!

    Have you tried any other local amp places?
     
  8. blasius01

    blasius01 Member

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    Thanks man... I do think that I'm gonna end up returning the power transformer ... i just keep hearing so many positive reviews from the OT that i just had to have one lol and yes this is for a CC.

    So you dont think the PT would help any???
     
  9. zzmoore

    zzmoore Member

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    Well, the question would be..... help what.?
    What concerns do you have about the present PT.
    I have worked on a few CC's and also own one. I have never seen any problems in these amps associated with the power transformer. Not saying it has NEVER happened, but it would be low/last on my list of things to replace.
    If you read enough stuff on this forum you will see guys swear they hear a difference in everything thing from 300 dollar power cords up to and including the color of the covering on coupling caps. But IMO.....no, I do not think a Merc Mag PT will help your amp any. There is no guarantee you will hear an improvement from the OT change. But, if I had to take a guess, I would say you will hear/feel a difference, but again, it may not be a "favorable" difference. You may think it is different but equal, if you know what I mean.
    Ask a guy like Mark Norwine, or Mike from KCA NOS tubes about OT replacement. They probably have A Million different stories between them, regarding OT "up-grades", and if it "helped".
    But if you can afford to take a peek.....go ahead, it is fun and educational. You can always sell that Merc Mag OT or save it for a future build.
    Do not discard Lemmings advice.
    If you really want to pursue this, contact me off the board when you are ready, and I will guide you through safely discharging the caps. You will need a meter, even a cheap 7 dollar Harbor Freight meter just to verify, to yourself, that the caps are close to ground potential. Think it over.
    Tubes and speakers are probably a "better" and more immediate way to improve your tone. But who stops there.......?
    Good Luck
     
  10. slimjw

    slimjw Member

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    Nothing to ad on the cap discharge tip except I would recommend having a tech do the work. Just wanted to chime in with some first-hand experience regarding the MM swaps. I replaced the OT and choke in my AC30CC with MM iron and the difference was NOT subtle. I was sort of blown away, frankly. It made an already good amp into something great.

    Describing tone is always subjective but to my ears the low end got more solid (still retained its inherent Vox characteristic) and made the sound a lot sweeter all around. The tech who did the work gets quantity discount from MM so the replacements were cheap enough to be a no-brainer. I kept the stock PT in mine, FYI. After this experiment I wouldn't hesitate to drop MM in any amp that was a candidate for better iron. Well worth the coin, IMO.
     
  11. Truxton Spangler

    Truxton Spangler Member

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    If the amp fears you the electricity will flow away from you. I learned this from Chuck Norris :)

    Best regards -T
     
  12. Boytbpc

    Boytbpc Member

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    THIS DOES NOT WORK ON ALL AMPS. DO NOT RELY ON THIS TECHNIQUE ALONE!!!

    K, now that has been said. I drain the caps by shorting them to a ground point using a modified VOM probe, I attached a 200K 5W resistor in line and an aligator clip to the end opposite the probe, insulated it, and voila, perfect cap draining device. Plus always check the caps with a VOM before you go dicking around inside an amp. Even if you are 100% sure that they are drained, check them anyway.
     
  13. Masco

    Masco Member

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    Get your money back/sell the PT and use the refund for getting your choke and OT replaced by a professional.
     
  14. Echoes

    Echoes Senior Member

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    I had the trannys replaced in a few amps....the biggest difference for the GOOD was with Mesa Rectifier amps...huge and very noticeable change in sound dynamics and musicality...I had a Brian May AC30 and changed the trannys in that with MM (by a pro I will leave un-named..he did a great job in the wiring and replacement and MM used my amp as a model to R&D a replacement as they didn't have one until my amp request) afterward it was VERY stiff and took away the sag, chime and feel of the amp...I wish I would have left the original iron in the AC30....YMMV.
     
  15. Cirrus

    Cirrus Member

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    I replaced the coupling caps, transformers and choke and did another couple of mods on my AC30cc last September with very little prior experience even of soldering. But I took care to research things like safe filter cap discharging at great length so I knew what I was getting in for, and when the parts arrived I had already made up a discharge cable with croc clips, a probe, a big resister and plenty of insulation tape, and had the amp open to identify the parts I was planning on changing, where the filter caps were, how the boards were connected together etc.

    My first surprise was that the filter caps had no charge in them - they actually drain very quickly down to a few volts within a minute of the power being turned off. But you should still have a suitable volt meter to check - if the resistors that allow them to drain have a faulty connection or are otherwise compromised then you might be looking at 400+ volts and easily enough current to kill you, so always check.

    My second surprise was how easy it was to take the preamp board out to change the filter caps and plate resistors. That made a big change in the sound of the amp, and I'd recommend it as a relatively cheap way of getting a sweeter vox tone out of these amps.

    Then it came to the big three - OT, PT and Choke. Firstly, I took pictures of where every wire relating to the transformers and choke connected to the PCBs and valve sockets, and the paths they took. Then I identified what the wires were.

    Regarding the power transformer, there are a number of secondary taps which each put off a different voltage. You should have a sheet that came with the PT identifying the taps by wire colour. What you need to do is make sure you know where those taps are actually going to be connected - that the ~300v tap goes to the rectifier, that the 6.3v taps go to the heater wires, that the 5v tap goes to the rectifier's heater, and that the 26v tap goes to the board that has the effects loop, reverb send/ return and tremolo circuits. I found the pictures I had taken before I took out the old transformer were invaluable for giving me the confidence that the wires were going to the right places. Fitting the PT was easy, the hardest part was keeping the wires wrapped neatly, tidily, and snipping them to the correct length to aid that.

    Oo, and the MM PT is so tall I actually had to cut a bit of wood away in the case to get the chassis to slide in again once it was all done and dusted.

    The output transformer was actually a bit more tricky for me, because the primary wires connect to the power tube sockets which were a bit fiddly, and the secondary wires connect to the impedance selector switch, which was a pain to solder through both connections, and the common lead goes to the output jacks in what is quite a tight and fiddly little arrangement of wires and fingers when it comes to manoeuvring a soldering iron. I actually made a mistake here, too - I connected up the impedance selector switch backwards, so it needs to be set to 8 ohms to get the 16 ohm tap. I think I'm going to re-label rather than re-wire that, something I've been meaning to do for a while...

    The OT was actually a different size to the stock Sanecore transformer, so I had to drill two more holes in the chassis, which had to be done with great care, obviously!

    The choke, for a little lump of metal with two wires to connect, was the hardest of the three. Because it, too, was a different size to the Sanecore choke so a hole had to be drilled for it. The problem is, directly under the choke is the board with the filter caps. I found that I didn't have to remove it if I drilled a hole that'd make the choke sit at an angle, so I did that, taking care to cover the PCB to stop any loose flecks of chassis from the drilling shorting something later on.

    Then once I'd done that, I found I had to remove the board anyway because I couldn't for the life of me get between the chassis and the board to tighten the nut that holds the choke on. So I had to unhook the resistors attached to the valve sockets and unsolder a bunch of wires to finish the job.

    In the end, I can't say exactly what effect each individual part had on the tone of the amp, because I did them all at the same time. There was definitely a change, and it was a change that made the amp more suitable for the sounds I want to get out of it. At high volume and gain, it no longer sounds flabby and harsh - the overdrive is powerful yet tight and focussed so it sits better in a band mix. The treble used to feel very "plastic" - hard to describe in technical terms but it just wasn't very pleasing to the ear, but now it's a much sweeter treble that chimes the way you expect a Vox to chime - bright without being harsh. The amp doesn't have noticeably more bass, but if feels more solid at all settings. And it also seems more dynamic and lively at all settings - more able to respond to the nuances of the guitar playing, and also the pedals I use to boost it - everything used to be covered by the same vox "pushed and not loving it" tone so that one overdrive sounded much like the other, but now you can really tell the difference, even when the amp is also being pushed - which it loves a lot more now.

    I know there are plenty of people on this and other forums who don't put a lot of stock in these kind of subjective descriptions of the advantages of "upgrading" amps like this, but to me it was worth it. Even if it were all in my head (and I don't think it is because I have a reference point in the form of two other vox ac30cc's - one stock, one with only coupling caps modded) it was worth it to me because I'm the one who has to be able to stand up on stage in front of people and know that I've got the instrument (yep, I consider my amp an instrument) that'll allow me to express myself.

    So it turns out I've written absolutely loads here. Hope it helps you, blasius01. If you do decide to do the work yourself, take your time, exercise caution with those filter caps, take your time, enjoy the feeling of having worked on your amp, take your time, and finally, take your time to be sure you know what you're about to do at each step of the way.
     
  16. blasius01

    blasius01 Member

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    THANKS CURRUS!!!! I ending up taking my amp to a tech... should be done in the next couple days. I sent the PT back and got my money back to pay for the tech. I read in alot of forums saying that the PT didnt make any notable difference in sound. Im sure its awesome to have but im ok with the stock one for now. BTW did you do the bight cap mod?? and also what coupling caps did you use??? Im actually not even sure what they are lol

    If it helps I play christian music and most of they styling is in the style of u2. does yours have that nice U2 chime???

    Thanks so much for taking time out to educate me:)
     
  17. zzmoore

    zzmoore Member

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    You made a couple of wise choices.
    I think you will benefit from your decisions, and will enjoy what I believe will be a "better' sounding and more versatile amp. I have had experiences duplicate to Cirrus. The money your tech charged you is completely commensurate with the task at hand. I have done this job a few times, and it is not "easy'. There is some fitting involved, and as always, lead dress to consider. These amps are capable of excellent tone and reliability.
    You did the right thing.
    Well Done :aok
     
  18. Cirrus

    Cirrus Member

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    No worries! I love these amps and it was great fun messing round with them.

    Yeah, I don't think the PT could make a huge difference in tone really. I mean, as long as it provides the voltages the amp needs, then it's doing it's job. I just wanted to do the whole bunch, almost as much out of curiosity as anything. One thing I noticed is that the stock European ac30cc power transformers are, I believe, designed for 230 volts, which is supposed to be a Europe wide standard. But here in the UK the standard is actually 240 volts, and in Birmingham where I practice it's frequently more. The MM PT I got had 220v, 230v and 240v primary taps, which made me feel a little bit less like I was overpowering the amp.

    I did the bright cap mod shortly after I got the amp and it did make the top boost channel much more usable with pedals. One of the mods I did when I had the amp to pieces last year was to put a lower value bright cap in, which I liked since the rest of the mods had the effect of taming what I considered to be harsh treble. It was a 68pf silver mica cap I believe. I've since taken it out, but I think I want it back in...

    The coupling caps were sozo's - the yellow ones. They made a noticeable difference (I've put them in another ac30 that is otherwise mostly stock) - with gainy sounds especially, they were sweeter. The coupling caps block DC current from getting through each stage of the preamp, only letting the AC signal of your guitar through, and they do add their own tonal colour as they do it. The other changes were changing the v1 plate resistors from 100k to 220k, which gives the first valve (the one before the gain knobs) less headroom and a little more growl - it seems to respond more readily to boosts and picking dynamics. Then I got rid of the cathode bypass cap for v2, which gives the top boost channel a little less gain and bass and more headroom, which leaves the top boost channel more chimey and vintage sounding but less gainy. On my other amp I wired up the standby switch to bring the bypass cap in and out the circuit and you can really hear the difference.

    Ah, that was the other mod I did to my main amp - I just bypassed the standby switch completely when wiring in the new PT. It's not needed and can damage modern rectifier tubes, so it felt safer just taking it out of the picture.

    I'm a pretty big U2 fan and though my band's music is quite a bit heavier, I still use that Edge clean chime with a strat as a benchmark. And yeah, these mods helped the amp deliver a nice Joshua Tree style clean tone.
     

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