How to repair a hand-wired Vox AC15 HW. Power supply problem and microphonic tubes.

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This hand-wired Vox AC15 had no sign of life. It was a straightforward repair, but I explored a couple of points to look out for on the way. If you are interested in how to repair an Vox AC15, or even tips on how to find power supply problems on other valve/tube amps, this video will be of interest to you.
If the Tech stuff is too boring for you and you want to hear the final result, jump to 11:10.
PS. If you need your amp repaired in Sydney Australia, give me a call. My details are at the end of this video and on my website guitaramptech.....

Опубликовано:

7 сен 2024

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Комментарии : 54

@DeadKoby 4 года назад

Good day. Fellow amp channel here. Welcome to the team.

@theguitaramptech 4 года назад

Thank you!

@philjackson3457 4 года назад

Well explained, and fun to watch. Thank you!

@theguitaramptech 4 года назад

Thanks Phil. I'm glad you enjoyed the video.

@philjackson3457 4 года назад

@@theguitaramptech Have you done any repairs/videos on a Vox AC10?

@theguitaramptech 4 года назад

Phil Jackson worked on a few. I bought one after repairing an AC10 for a customer. I’ll run through the amp mods in the coming weeks. If you subscribe and hit the Bell icon you’ll get a notification. Thanks Phil.

@gridsanddots7805 4 года назад

Looking forward to the AC10 repair video!

@theguitaramptech 4 года назад

Grids and Dots. You got it, Carmen 😉

@gerrickreidenbach8147 4 года назад

Really helpful videos, Chris. Liked and subscribed. Thanks for posting, you're a YT star!

@theguitaramptech 4 года назад

Thank you so much, Gerrick. You’ve made my day 😁

@gerrickreidenbach8147 4 года назад

@@theguitaramptech You make my day better when I see a new video posted from you. Especially during this global pandemic. You are really helping me understand a better method for diagnosis of problems, tools and techniques for competent repair. I've got a long way to go, in that respect, but finding entertaining and informing videos that have a degree of taste can be challenging. Thank you, again. The world is a better place because of you, really!

@vincentl.9469 3 года назад

Hi Chris...I had a look at one of these once- decided against. The AC15 model goes back to '58 ,which reminds me, have you ever met Hank Marvin? He moved out to Perth some years back. Hank was the first 'ambassador' for Vox in England from the late fifties and not the Beatles...although they did a lot to promote the brand later on...

@theguitaramptech 3 года назад

I love the AC15. I had a red one! It played better 🥰

@dalton.nascimento Год назад

Great content! I wish you were based in my city to take care of my amps haha Random silly question - I’m about to bring my bought in US AC15HW to Europe/Spain, do you know what’s the best way to use it in the 220v environment here? I’ve read step down coverters might not be ideal due to the 50hz frequency but not sure if the stock transformer can be rewired to 220v, do you know if that’s possible? Tks a lot

@theguitaramptech Год назад

Thank you for your lovely comments, Dalton. I haven't done a voltage conversion on an AC15, so I can't advise you if it has multiple primary power options. You would need a 220 to 120V STEP DOWN transformer. Make sure you have sufficient wattage in the step-down. I think your amp uses a 1.25A fuse at 120v. So Vox feel that it won't use more than 150w when operating normally. Double that for your transformer and order a 300w step down (absolute minimum of 200w). A step down works for for home/studio use, but if you plan to gig with it, get a new power transformer. I would recommend you get it from Vox to ensure you will have the correct secondary voltages.

@dalton.nascimento Год назад

Tks a lot for the crispy explanation, I’ll definitely keep this in mind when buying the step down transformer. Cheers

@moodyga40 4 года назад

I repair and build valve amps in Sydney too

@theguitaramptech 4 года назад

Very cool, Ian

@whatsstefon 4 года назад

Blue Mountains valve amp tech between tours here.

@theguitaramptech 4 года назад

@@whatsstefon G'day mate. We met a while (>12 months) at Katoomba Music. Enjoyed our chat. See you on my next visit.

@whatsstefon 4 года назад

@@theguitaramptech Ah yes. You looked familiar. But I couldn't place it. Nice one! Such a small world. Glad to see you're throwing content up on RU-vid. There aren't many of us tube amp techs around, and with the sad loss of Vito only a little while ago, it's now an ever smaller world. I am gonna subscribe to the channel matey, looking forward to seeing some great repairs, and hopefully learning too.

@theguitaramptech 4 года назад

Stefano Musica thank you stefano. I’m honored to have you aboard

@rods4548 5 месяцев назад

Would you know the value of the MOV or the ICL surge protector of the Vox AC15C1 soldered between the A/C receptacle in the back and the on/off switch? Thank you!!

@theguitaramptech 5 месяцев назад

HI Rod. I might just define the function of a couple of components. An NTC Negative Temperature Coefficient Thermistor is a type of Inrush Current Limiter and is in series with the Active/Live wire. Its resistance starts high and reduces with increasing temperature/current thereby reducing the (often savage) spike in inrush current. A MOV Metal Oxide Varistor goes from Active to Neutral. It starts with a very high resistance and is designed to fail “short” with a large spike. It will blow the fuse in order to protect the circuit that follows. I think I remember the NTC part number, but without being 100% sure, I prefer not to say. I would hate for you to bring the burnt carcass of your AC15 to my front door and say “You remembered wrong!”. Besides, it will be a good exercise for you to learn how to determine the NTC.

@rods4548 5 месяцев назад

Just in case somebody else needs this part and doesn't think "it will be a good excercise to learn how to determine the NTC", here's the part number:SCK15105MSY.

@jamessbca 3 года назад

Yeah. Topping it out with some Living Colour!!!

@theguitaramptech 3 года назад

Ha! My goal in life is to be as good as Vernon's fingernail clippings. Unlikely I will ever get there

@Splattle101 4 года назад

Nice vid about a nice amp. You expressed a preference for Weber speakers and I wholeheartedly agree when looking for speakers for my Fender style amps. Which Weber would you favour in place of the Celestion Blue or the Greenback? I've used their 12F150s and a slew of their 10" AlNiCo speakers, but they'd all be too bright to replace a Celestion. I'd be interested to hear your view.

@theguitaramptech 4 года назад

Thanks for your question, Bladder (I love that name). There are only a few speakers that I like as much as Webers. One is the Celestion Blue, another is the EVM12L and the JBL D130. I like a ribbed cone. I am not a fan of speaker distortion. Speaker distortion is out of our control and it may not be how you want to colour your sound. I also liked the Brit-made Greenbacks, so if you ever get one of those, hold onto to it. The Chinese ones are OK, but not a patch on the originals. After this its all a matter of taste. I tend to like the open sounding chime of ALNICO speakers, but I have heard some mighty fine Ceramics. Ironically, I took out a beautiful sounding 1960’s Jensen from my drip edge Princeton and put in a Celestion Blue (new 12” baffle). Heresy…but I love it. Thanks for your question. Don’t we love nerding out!

@theguitaramptech 4 года назад

My first Weber speaker was about 25 years ago. After talking to Ted, he suggested the speaker (which I still have) that eventually became the Ceramic Blue Dog. Nice. www.tedweber.com/blue12f

@swenpaylay 3 года назад

Hi thanks for the video. For a newbie, where/what was the fuse you replaced?

@theguitaramptech 3 года назад

I wish I could remember, Tom. Sorry mate.

@moodyga40 4 года назад

That black disc looks like a posistor

@theguitaramptech 4 года назад

Thanks for your reply Ian. A Posistor has a postive temperature coefficient, which means the resistance would increase with temperature, which is not the case in this application. I think in the video I said it was an MOV. An MOV is across the supply and not in series as this component is. (Note to Self: Engage brain before mouth) I should have said an NTC. A Negative Temperature Coefficient Thermistor reduces its resistance with increasing temperature reduces to reduce the current surge usually on the primary side of the power Tx. Thank you for alerting me to my brain malfunction, Ian.

@moodyga40 4 года назад

@@theguitaramptech we all make boo boos, i am building myself a class A amp at the moment. 807 output tube EF37A preamp driver tubes i meet you when you came to Speaker Hospital to get a speaker fixed

@vincentl.9469 3 года назад

Chris...how often have you bought new tubes on the same amp? I hear of people keeping the same tubes for 10 years or longer...sometimes difficult to know -unless there's an obvious change in sound..

@theguitaramptech 3 года назад

That’s a difficult question for a general answer, Vincent. Cathode biased amps like vox, run the tubes hot, at around 100%. I would think 1yr is a realistic expectation of tube life for a gigging musician. 6L6s biased at 60% could last many years. While new production tubes are very good, they’re still not as good as the tubes from the 60s. Ive often tested the original tubes in a 60 year old Fender as strong. Amazing.

@vincentl.9469 3 года назад

@@theguitaramptech the other thing is so long as people keep buying tubes- they'll keep making making 'em ! which should maintain quality, and keep costs down ..have to see

@theguitaramptech 3 года назад

@@vincentl.9469 True. If people cave in to the lure of digital modelling, the tube future will become much more exclusive. A similar fate to when we compromised on the sound quality of Vinyl and CD and decided that MP3 was good enough.

@vincentl.9469 3 года назад

@@theguitaramptech Hi Chris..thinking back to this post...you must have heard the latest story on tubes from the boss of Electro Harmonix talking about a shortage of tubes world wide; the main tube factory in China has closed..whether that's ,permanent not sure; or it could be his way of getting people to buy more tubes right now while stocks last! that does no good either...

@theguitaramptech 3 года назад

@@vincentl.9469 no, I haven’t heard that. That is definitely a concern. I better look into this further. Thanks for the heads up, Vincent

@m1km1sh1n 3 года назад

😃👍

@theguitaramptech 3 года назад

Thank you

@RRiley6 2 года назад

I went here to see why my amp wasn't firing up and it turns out I've blown the same fuse!

@theguitaramptech 2 года назад

That's what I call a good outcome, Robert. Well done.

@johnsimms3957 4 года назад

It looks like the owner played the tubes until they failed and blew a fuse.

@theguitaramptech 4 года назад

That's a possibility, John. Or a knock sufficient to short the filament to the cathode of a EL84 running on 100% idle bias current? One of the joyous mysteries of tube amps.

@judysinclair 4 года назад

Haha!!! Or maybe pulled them out and jumped on them?

@analogaudiorules1724 4 года назад

The real issue i see is vox using cheap Chin*se crap capacitors on a unit that costs 1,000 plus usd... in a kit like this, there should be nothing but the best, united chemicons, cde, Panasonic, vishay, nichicon, kemet eletrolytic capacitors which have well established track records, there shouldn't be ANY COST CUTTING "JACKON" CRAP inside this unit like what is clearly shown at 2:20. If I'd ever buy one, all those crummy cheap under performing capacitors would be changed out for longterm reliabilitys sake immediately.... Not only will it be more reliable, it'll sound better to and be far more stable... its disgusting that something so expensive uses inferior parts, uk and hand made... like come on vox.... I wouldn't send that back to a customer with parts like that. Vox needs to switch out all that junk with cde tta or vishays tte or 3od series at the very least, it isnt worth saving the 5 bucks...

@theguitaramptech 4 года назад

I must admit, I do like Vishay components. A but dearer than most, but I have never had a failure.