New Sluckey AC15 build - a couple of questions

[Eythor]

Hello everyone

I'm considering doing an AC15 build and before I order the parts, I have a qouple of questions.

1. Mouser doesn't seem to have a 20" chassis that's suitable for this and since I'm in Europe, ordering from multiple sources is going to be very expensive. Therefore, I'm thinking about going for a 17"x10"x3" Hammond chassis, which is the longest I can get. Looking at the PDF with the chassis layout, it looks like it should be fine, and the 10" height will give me more room to maneuver compared to the 6 1/2" of the original build, but I wanted to see what those who have built the amp have to say. It's going to be a head so a shorter chassis is definitely a plus since it will make the head look more proportional imo, but I want to make sure I can actually fit everything in

2. I have a NOS 12AT7 lying around I thought I'd use in the phase inverter. Whether it sounds better than a 12AX7, we'll see, but is it definitely safe for this amp? Also, will a 12AX7 work for the oscillator?


One last thing, I haven't seen a single sound demo of this amp. Not even in the build threads I've read. Does anyone have a link to one?

Thanks a lot!

[dwinstonwood]

Hey Eythor,
I built a single channel AC15 based on sluckey's version. I used the Brown 6G2 Princeton chassis which is 17.25" x 7.125" x 1.75" in size. Since the 6G2 is a popular amp project, the chassis and cabinet should be easy to source in Europe, I would guess. And, the only holes I had to drill were to mount the turret board and the choke (which I put inside the chassis). I did have to use adaptor plates for the 9-pin EL84's and the EZ81. Here're my drawings:

[sluckey]

My original AC-15 was designed to fit a 17" chassis. As far as I know, only one was ever built and that was by forum member "lego4040". He has a thread about the build in this forum. The build used a Fender style cap board plus the shorter main board.

Docs are here...   http://sluckeyamps.com/VAC15/Vox_AC15_short_board.pdf

I have a NOS 12AT7 lying around I thought I'd use in the phase inverter.

Try it. If you don't like it then use a 12AX7.

Also, will a 12AX7 work for the oscillator?

Huh??? The oscillator is a 12AX7.

I don't recommend the hammond chassis. Too flimsy.

[Eythor]

Hey Eythor,
I built a single channel AC15 based on sluckey's version. I used the Brown 6G2 Princeton chassis which is 17.25" x 7.125" x 1.75" in size. Since the 6G2 is a popular amp project, the chassis and cabinet should be easy to source in Europe, I would guess. And, the only holes I had to drill were to mount the turret board and the choke (which I put inside the chassis). I did have to use adaptor plates for the 9-pin EL84's and the EZ81. Here're my drawings:

Thanks! I definitely want the two channels and tremolo, though, so I'll be going for a full build 

My original AC-15 was designed to fit a 17" chassis. As far as I know, only one was ever built and that was by forum member "lego4040". He has a thread about the build in this forum. The build used a Fender style cap board plus the shorter main board.

Interesting! It's good to know that there are some different routes I can go. In your 20" chassis layout, there is a lot of space on the left. Are there any downsides you can think of to moving the board 3" or so to the left? All I can think of is the fact that the PT would be slightly closer to the preamp section but I wonder if it would even make a difference.

Also, will a 12AX7 work for the oscillator?

Huh??? The oscillator is a 12AX7.

Sorry, my bad! I was thinking of the modulator which is a 12AU7.

I don't recommend the hammond chassis. Too flimsy.

Do you know of any places in the US that have sturdier chassis? I looked at Mojotone but they only have pre-drilled ones.

I may have to find some turret boards as well. Digi-Key and Mouser have turrets but I don't think they have any blanks suitable for making turret boards. All I can find is 1.3mm thick PCB blanks, which would surely be too thin. Looks like I'll be forced to order from multiple sources after all 

[sluckey]

In your 20" chassis layout, there is a lot of space on the left. Are there any downsides you can think of to moving the board 3" or so to the left? All I can think of is the fact that the PT would be slightly closer to the preamp section but I wonder if it would even make a difference.

One big downside. The board, front panel layout, and tube layout were all carefully planned to work together to provide neat, logical, and short wiring. If you shift the board to the left by 3", then the length of all the tube socket wires will need to be increased by 3". Lot's of potential problems with longer wires.

[sluckey]

This good guy on eBay will probably make any length chassis you want. Here's a 17x6.5x2.5...

     https://www.ebay.com/itm/224398633901?hash=item343f336bad:g:1PAAAOSwQEpdYXR~

Maybe Ed Chambley will drop by. He's built more of my AC-15 than anyone.

[WiderGates]

Hello Eythor,

do you know Tube-Town located in Germany?
They have all you need to build a 15 Watt with Tremolo they call TT 18 Watt and several slightly different models.

Link to the whole kit.

Link to the chassis.

Chassis without cutouts:
TT-Chassis 008 - 490 x 200 x 65

[mresistor]

This good guy on eBay will probably make any length chassis you want. Here's a 17x6.5x2.5...

That is doubtful.  I've asked before and they refused. I even asked if they would make a Marshall 1974 combo chassis copy and that hasn't materialized.  But you could ask, you never know.

[acheld]

This guy is fast, accurate, fair price and totally custom.

https://seasidechassisdesign.com

[Lectroid]

This good guy on eBay will probably make any length chassis you want. Here's a 17x6.5x2.5...

     https://www.ebay.com/itm/224398633901?hash=item343f336bad:g:1PAAAOSwQEpdYXR~

I've just gotten one of his chassis', a Princeton Reverb, and it's good quality.  He's recently started using 18ga steel instead of the thicker 16ga, to hold his prices, but I think the 18ga is more than sturdy enough.

[Eythor]

Thanks a lot for the suggestions everyone! I ended up finding a supplier in Europe which makes a ~19" chassis out of thicker aluminium than the Hammond ones at a very reasonable price. They also have turret boards and all the stuff Mouser doesn't carry, and shipping cost is very reasonable. Looks like it will all work out.

I'll post an update once the parts arrive and I start building 

Since everyone here seems pretty down to earth, and perhaps not as easily caught up in the hype you see on boards like TGP and TDPRI, I thought I'd ask: on a one-off hobbyist build, is it worth paying more for "premium" caps, like orange drops for example? It's roughly a $30 difference in cost compared to going for generic caps, so it doesn't make a massive difference on a $500 build, but I'm interested in hearing people's opinions.

One big downside. The board, front panel layout, and tube layout were all carefully planned to work together to provide neat, logical, and short wiring. If you shift the board to the left by 3", then the length of all the tube socket wires will need to be increased by 3". Lot's of potential problems with longer wires.

That's something I hadn't thought about and will definitely have to keep that in mind. I'll be using a 19" chassis so there will be some slight adjustment needed.

[sluckey]

If you intend to make a board using my template, the physical size of the caps is way more important than the cost of the caps. My board was designed to use small caps like the Xicons sold right here by Hoffman. Take a look. Orange drops will not fit on my board...



This will fit a 19" chassis with only slight adjustments. Very doable. Just keep the basic relationship between the front panel, board, and tubes.

[jim]

If you are using the heavy transformers that Sluckey used in his build including the huge choke you should really use a steel chassis-- the aluminum will sag or twist especially if you like to remove the chassis and tinker a lot.  You can also solder a ground buss to steel.   As caps go:  In this country we call this conundrum a "opening a can of worms" and everyone has an opinion.  Mine is I cant really hear the difference between polyester, film, or polystyrene.   Its all plastic to me.   But that being said, an extra 30 dollars isn,t so bad to spend on your amp.    Jim

[mresistor]

I can't tell any difference between the Xicon chicklets and more expensive caps like ODs or Sozo  ..   

[Eythor]

If you intend to make a board using my template, the physical size of the caps is way more important than the cost of the caps. My board was designed to use small caps like the Xicons sold right here by Hoffman. Take a look. Orange drops will not fit on my board...

Thanks for the heads up. I didn't realise how much bigger the orange drops are. I will have to find something else then.

Are the white ones you've used in the power section Mallory 150Ms? For the big filtering caps, I've gone for F&T. I believe they're smaller than the Atoms so hopefully that should work alright.

Also, while I have you here, is there any reason why I couldn't omit the standby switch? Given the choice, I prefer not having one.

If you are using the heavy transformers that Sluckey used in his build including the huge choke you should really use a steel chassis-- the aluminum will sag or twist especially if you like to remove the chassis and tinker a lot.  You can also solder a ground buss to steel.

I really wish undrilled steel chassis were easier to find. All I'm seeing is pre-drilled kit chassis 

I will look around and see if I can find one. My first thought was that drilling out and filing the IEC slot on a steel chassis would be an absolute nightmare.

Do you think that it would sag even if it's made out of 2mm aluminium? I don't plan on soldering directly to the chassis so that's no big deal.

[sluckey]

My chassis is .08" (2mm). It does not sag.

[acheld]

I really wish undrilled steel chassis were easier to find. All I'm seeing is pre-drilled kit chassis

I get all my undrilled chassis from https://seasidechassisdesign.com -- like sluckey, I use the 12ga aluminum (2mm, or 0.08").   It is surprisingly rigid.   Steel is also available, but I really like the workability of aluminum.

You can get "standard" designs, but I just email the guy the dimensions I want and there it is, done.  If I need something a little different, I include a drawing in the email.  No muss, no fuss.

No, I don't get a commission, but I support artists who give good value . . .

[Eythor]

The parts are ordered and should be here sometime this week. I have a Bachelor's report for university due on Friday so I'll wait until that's finished to start building 

I'm really looking forward to seeing how it turns out. I've had an AC15C1 before but I reckon this one will sound quite different.

[Eythor]

I've been away for a while. All of my parts arrived 2-3 days after ordering, except one shipment that didn't ship until 5 days later and took a couple of weeks to arrive.

Anyway, I was apple to make the turret board and solder on the components. Now I'm working on drilling out the chassis before I start assembly.

I have one question: I noticed that Sluckey runs resistors from the board to the cathodes of the EL84s, while the layout diagram shows wires. What is the difference?

[sluckey]

I have one question: I noticed that Sluckey runs resistors from the board to the cathodes of the EL84s, while the layout diagram shows wires. What is the difference?

Those 1Ω/1W resistors were added after all the document files were completed. Maybe I should update the docs to show those resistors. They are not necessary but they make it easy to measure the current for each tube. This allows you to match output tubes. Simply measure the mV across each resistor and mentally convert mV to mA. The mV is the same as mA since the measurement is taken across a 1Ω resistor.

BTW, nice workmanship on the turret board. Did you find an appropriate chassis?

Also, would you post a reply in this thread and tell member raphaelctt where you got your blank board? He has an issue with his board but cant find a suitable blank in Europe. Thanks...

     https://el34world.com/Forum/index.php?topic=29015.0

[Eythor]

Those 1Ω/1W resistors were added after all the document files were completed. Maybe I should update the docs to show those resistors. They are not necessary but they make it easy to measure the current for each tube. This allows you to match output tubes. Simply measure the mV across each resistor and mentally convert mV to mA. The mV is the same as mA since the measurement is taken across a 1Ω resistor.

I guess having them doesn't hurt. I'll see if I can find some locally.

BTW, nice workmanship on the turret board. Did you find an appropriate chassis?

Thanks! I went for the basic one from modulus amplification.com. It's around 18.4" and made from 2mm aluminium. Very reasonably priced at £39 as well. The only downside is that it's not welded or riveted, so I can't put much weight on the lock nuts. My plan is to build a head and have the amp slide into a "shelf", upside down, so it shouldn't be an issue. I went for a somewhat Matchless inspired control layout. I didn't really have much choice as the chicken heads need a lot of space and, in my opinion, a Vox needs chicken heads.


Because of the shorter chassis, I had to get a bit creative with the common ground bus placement, but I think it will work.

[Eythor]

Progress has been quite slow but I'm trying to get the filament wiring done today. To make sure I understand it correctly, one side goes to pins 4 and 5 on the 12ax7s and 4 on the EF86, EL84s and EZ81, while the other goes to pin 9 on the 12ax7s and pin 5 on the others, correct?

[sluckey]

That's correct.

[Eythor]

I finished wiring up the power supply today. Everything seems good so far. With the power transformer wired for 240v and 242V at the mains, I'm getting around 6.8V on the filaments and 588V across the high voltage secondaries.

I will try to get the controls wired up today as well.

[Eythor]

It's almost finished now. I just have to hook up the impedance selector switch to the speaker jacks and connect the footswitch. It's almost midnight here so I'll wait until tomorrow to test it.

[Eythor]

I've tested the amp and everything works great. Sounds amazing as well through the greenback in my Marshall 1974x.

Surprisingly, I do prefer the sound of the tremolo channel over the normal. It's a bit livelier. Jumping the channels is my favourite though and I'm glad I went with the jump switch. Blending in a little bit of tremolo so that you only hear it when chords ring out is really special.

The only "issue" is the tremolo circuit as it gets a bit "wobbly" on full depth. No big deal. The tremolo is off by default until I plug in a cable. I've connected the footswitch wire to tip and I'm not using a jack that grounds itself when unplugged. Does this seem right? Will I perhaps need a "switching" jack for this to work properly?

[sluckey]

You need a switching jack wired to ground the tip when no footswitch is plugged in.

IMO it's better to leave the oscillator running full time by hard wiring R65 and R68 to ground. Then simply kill the oscillator signal by putting a ground on the Depth pot wiper with the footswitch. The tremolo will now be on by default.

[wsscott]

This is for anyone who wants to reply.  I've been looking for a new project, and I've done a couple of projects based on Magnatone, which Sluckey and others were really helpful with.  I've been very pleased with them.  I've never heard a VOX live, just on recordings, so don't really know its sound or what people prefer about it vs. a Fender or Magnatone.  So, if I'm considering a build for a "studio" size amp, it sounds like a 15 watt would be a good choice.  What are your thoughts on the differences between this VOX build and that of a Fender or Magnatone, ie. sound, and other playability issues?

Also, what's the benefit of having 2 channels, ie. with and without tremolo?  I know a lot of amps separate them, but why do that, since nowadays you don't have multiple guitars playing out of the same amp.  Why not just have 1 channel with a Normal and Bright input, and a tremolo that you can just turn on/off?

Did any of the VOX models have Reverb and Tremolo?  Is there a benefit to not adding Reverb?

Thanks as always.

[Eythor]

What are your thoughts on the differences between this VOX build and that of a Fender or Magnatone, ie. sound, and other playability issues?

It sounds chimier and sweeter than a Blackface Fender imo. The Fender  will also have quite scooped mids  while the Vox doesn't. I use a Deluxe Reverb clone, which is very versatile, as my main amp while the Vox is a lot of fun to play when you're in the mood for that sound.

Also, what's the benefit of having 2 channels, ie. with and without tremolo?  I know a lot of amps separate them, but why do that, since nowadays you don't have multiple guitars playing out of the same amp.  Why not just have 1 channel with a Normal and Bright input, and a tremolo that you can just turn on/off?

It's just the way it was done back then by Fender, Vox, Marshall, etc. If you build it with just the tremolo channel, you'll have exactly what you described. I like having both channels as they're voiced differently and blending them can sound great as well.

Did any of the VOX models have Reverb and Tremolo?

I've never seen a (vintage) Vox with reverb and my '64 AC30 didn't have one. Almost all, if not all, Vox AC amps have tremolo.

Is there a benefit to not adding Reverb?

Simplicity. My take is that a Strymon Flint will sound as good, if not better, than the majority of built-in reverbs so it's not worth going through the hassle and expense of adding a reverb to a  build of an amp which didn't have one originally.

All in all, I'm really happy with this build. It is not as refined as many modern amps; there is a big volume difference between the channels, because of the extra gain on the normal channel, and it feels like some of the knobs go outside their usable range. But it just adds to the charm in my opinion. The tremolo is so much better than what my AC30 had.

Another thing to consider is that if you want to add the Vox sound to your collection, there aren't that many good modern production amps. Especially with an EF86, which I feel is an essential part of the sound. This build sounds at least ten times better than the AC15C1 I had for roughly the same price and reminds me a lot of my AC30 sound wise. Of course, there is the Matchless C30, which sounds absolutely amazing, but will cost 3-4 times as much.

[HotBluePlates]

Did any of the VOX models have Reverb and Tremolo?  Is there a benefit to not adding Reverb?

Reverb was available as an add-on module for all the amps (see one installed here).  It would be mounted in a back-panel cutout, just like the Top Boost add-on module.

A very few amp modules had built-in reverb.

Since Tom Jennings refused to pay Hammond to license their circuit (and then have access to their tanks), a single-spring system with crap transducers was developed.  And so they sound bad & most folks avoid using Vox' reverb.

But nearly every amp model had tremolo, or vibrato, or both at some point in time.