Finally building Sluckey's AC15 amp

[bnwitt]

So I have finally landed myself a position that gives me my weekends free again.  The unfinished studio reformatting is nearing completion.  I just received my Epi 1959 southern fade Les Paul Standard and am waiting on some hardware to upgrade it.  All I need in my studio now is a Vox AC amp. 


During my job overwhelm mode I was researching the hand wired Vox AC15HW1X and the AC4HW1 thinking about just buying a finished amp to get my missing Vox tone for the studio, but neither of them has the famous 1960 vibrato or even a tremolo effect.  So, I am on the verge of building Steve's 1960 AC15.  I know a few of you have built Steve's version, and I would like to hear your opinions on the vibrato's recordability.  Especially you Steve.  Building this amp is a lot of work and I can get a used AC4HW1 for $600 to just do the stock jangle tone.  I have built so many amps I don't need the "look what I did" satisfaction, I just need some great, versatile Vox tone for my studio and since my Genres are Country and Adult Contemporary the tremolo or vibrato effects are very useful in a mix. 


I already have my Hoffman BFDR and my Hoffman BFPR with tremolo, but I don't have the phase shifting vibrato.  Is the vibrato worth the price of admission?  Steve mentions in his write up that it is not quite as good as a Magnatone so I'm curious if there is a way to improve it in this build.  I really want a versatile Vox amp for the Studio and I'm looking for advice on how to proceed.  Tonal opinions are desired.  BTW, Does anyone know of any recordings which have that early Vox vibrato used?  Thank you all in advance for your responses.
Barry

[tubeswell]

BTW, Does anyone know of any recordings which have that early Vox vibrato used?

[jim]

That clearly demonstrates the difference between volume modulated tremolo and pitch modulated vibrato. The vibrato has a Doppler effect similar to a rotating Leslie speaker.  Jim

[bnwitt]

Thank you tubeswell.  I also found an Uncle Doug video with the Magnatone Panoramic amp dissected and demonstrated.


https://www.youtube.com/watch?v=tFXrJEwlsNg&ab_channel=UncleDoug

[bnwitt]

That clearly demonstrates the difference between volume modulated tremolo and pitch modulated vibrato. The vibrato has a Doppler effect similar to a rotating Leslie speaker.  Jim

Indeed.  The Uncle Doug video I linked even shows the two on the O'Scope.  Thanks Jim

[sluckey]

Hi Barry... The AC-15 vibrato pales by comparison to even the single stage modulator Magnatone amps. It's neat but not worth the circuit complexity IMO. OTOH, the AC-15 EF86 (normal channel) really nails that chimey Vox sound, especially with the right speaker. Ed Chambley built quite a few of these for the Atlanta area. He could probably give you a much better review.

If my main objective was a good Vox tone, I'd just build something like my Dual Lite amp. It is the Vox AC-15 EF86 channel with a Marshall 18W IIB preamp added. This makes a very versatile amp IMO.

If my main objective was a great vibrato sound then I'd buy a Bigfoot FX Magnavibe. There's one on reverb.com for $160 right now. Lots of youtube demos too. If I didn't already have two Magnatone amps, I'd buy this pedal right now! 

[bnwitt]

Hi Barry... The AC-15 vibrato pales by comparison to even the single stage modulator Magnatone amps. It's neat but not worth the circuit complexity IMO. OTOH, the AC-15 EF86 (normal channel) really nails that chimey Vox sound, especially with the right speaker. Ed Chambley built quite a few of these for the Atlanta area. He could probably give you a much better review.

If my main objective was a good Vox tone, I'd just build something like my Dual Lite amp. It is the Vox AC-15 EF86 channel with a Marshall 18W IIB preamp added. This makes a very versatile amp IMO.

If my main objective was a great vibrato sound then I'd buy a Bigfoot FX Magnavibe. There's one on reverb.com for $160 right now. Lots of youtube demos too. If I didn't already have two Magnatone amps, I'd buy this pedal right now! 


Thanks Steve.  Great information.  I'll check out the Bigfoot BX Magnavibe and the dual lite amp.  I might just end up buying a Vox AC15HW1X and put my labor into the studio.

[Ed_Chambley]

Hey Barry, just build one.  I have built more than 6 and I have to say the EF86 channel with a usable 12ax7 channel is needed to really open this amp up.  You will never know unless you build one.  It should have a Celestion Blue to play through.


The vibrato is NOT the amps glory and not often used by me or anyone else I have built this one for, but leaving it out loses too much since tremolo is present.


Many ways to pitch shift, but quality of recording is is subjective.  The Vox is not heavy, but a light warble.  I have found a strong warble to be desired live, but more often than not when recording I use less.  Your milage will vary according to your need, of course.


This is the only amp that goes with me everywhere.  It has gain, sparkle, overdrive at low volume, gets over a drummer and as the Brits say, It is Smashing!

[bnwitt]

Ed,
I have decided to build one.    Which of Steve's mods did you employ?


Steve,
What size chassis did you use on this amp?  Never mind.  I found it in your documents.  Can I get your most current Visio file?
thanks

[sluckey]

Can I get your most current Visio file?

Too big to post here. Check your PMs.

[bnwitt]

Thank you sir. 

[Ed_Chambley]

Ed,
I have decided to build one.    Which of Steve's mods did you employ?


Steve,
What size chassis did you use on this amp?  Never mind.  I found it in your documents.  Can I get your most current Visio file?
thanks

I have done many.  My favorite and how my amp is.  Both channel Preamps all the time. Volume for each and input for each. and slowed the tremolo and have taken the brilliance cap off the board and made capacitor switching for lower and higher frequencies.  12 in all and I actually use most of them since I use the amp to play everything.

[bnwitt]

Thanks Ed.


So, I purchased an AC15C1 for $400 to use for the cabinet on this build.  It looks like it utilizes a "C" chassis so I'll have one made to fit the space in the cab and will work around the back panel wholes or fill them in before re-tolexing it.  I can't make up my mind between red or fawn tolex.  I even like the cream tolex.

[sluckey]

FWIW... My odd front panel works very well with my board and tube layout. If you deviate much from my layout you will likely end up with some long wires crisscrossing. Also be aware that the row spacing on my board is 1/4". Hoffman provides a board for my layout.

[bnwitt]

FWIW... My odd front panel works very well with my board and tube layout. If you deviate much from my layout you will likely end up with some long wires crisscrossing. Also be aware that the row spacing on my board is 1/4". Hoffman provides a board for my layout.

Steve,
Thank you.  Yes, I've been studying your design for quite some time and intend to replicate it.  The only thing different I might do is use a set of my S2 18 watt trannies I've had around for quite some time.  If I have to alter the chassis cut out on the AC15C1 cabinet to accommodate it, I will.  I bought Doug's version of your board quite some time ago.  I've just been sitting on my hands for a while.  LOL  But actually as J.L. said, "Life is what happens when you're busy making other plans."
Last weekend, front brake job on wife's car.  This weekend, rear brake job on wife's car.  After that, Epi 59 LP standard mods.  And then the Sluckey AC15 project begins.  Unless my brakes go out.  LOL

[sluckey]

Be sure to use a beefy choke because output tube plate current flows through the choke. There will be 100mA flowing through the choke at all times.

[bnwitt]

Be sure to use a beefy choke because output tube plate current flows through the choke. There will be 100mA flowing through the choke at all times.

125ma or higher?

[sluckey]

125mA should be fine. My donor choke was rated for 100mA but seems to be fine. If I was buying a new choke I'd go for 125mA. I listed two Hammond chokes on the schematic. I actually measured the B+ current and it was just a little bit under 100mA.

[bnwitt]

125mA should be fine. My donor choke was rated for 100mA but seems to be fine. If I was buying a new choke I'd go for 125mA. I listed two Hammond chokes on the schematic. I actually measured the B+ current and it was just a little bit under 100mA.

Thanks Steve.  Hope to get started with this soon.  Too many honey doos dropping in my lap lately and then today my left eye was killing me and the optometrist found a small piece of plastic in my cornea.  I'm starting to feel like Job.  LOL  Brake job this weekend and then hopefully the build begins.


Barry

[bnwitt]

So who are we using to make our reverse engraved amp plates now that BNPLasers retired?

[bnwitt]

Does anyone have a faceplate engraver they recommend?

[JPK]

Does anyone have a faceplate engraver they recommend?

Below is a recent thread that might be useful.


https://el34world.com/Forum/index.php?topic=23946.0
.

[bnwitt]

Thanks JPK

[sluckey]

Have you made any progress?

[zircontweezer]

Does anyone have a faceplate engraver they recommend?

For the last couple of years/builds I've been using Inkscape (with a good example file of numbered dials) to create the faceplate then I export as a png and import it to a pdf with Foxit then my local engraver/trophy shop can produce it for $30 AUD per plate with a laser and traffolyte. Inkscape is free and I create the background layer (whatever size the plate is) then the "holes" layer then the "dials" layer and then the "text" layer. You then get to learn about sizing and centering and definitely locking and unlocking layers before you change stuff 

[bnwitt]

Have you made any progress?

I just received the chassis for my VHT head cabinet that I am using for this project.  I had to have it custom made as this head cabinet is a bit wide.  Now I have to make the cabinet look Voxy and I have to drill the blank chassis.

[bnwitt]

Zircontweezer,
Thanks for that info.  I'm a Visio guy from way back in 1995 before Microsoft bought the program.  I do my plates in Visio, print them to PDF and then convert them to Corel Draw files which most engravers can use.  I may have to change that output format since Corel has gone the way of the dinosaur.  I will check with precision on their file type needs.  Those plates look great.

[bnwitt]

Ok, so while I'm waiting on parts and doing my Visio layout drawings for this amp.  A Vox AC15HW1X (alnico Blue version) popped up on Reverb for $1,300.  Since that is $600 less than new, I bought it.  I powered it up and with no signal it is very hissy.  There are lots of CC resistors and low grade capacitors in it but I'm wondering if this hiss is normal for this version of the amp.  Has anyone worked on this amp model?  I'm wondering if replacing all of the CCs and low grade caps plus messing with the lead dress might make this a usable amp or if I should pop in a Sluckey build in a U channel blank chassis that fits and use this as the donor body.  Any opinions?  I can't have a hissy amp in a recording studio.  The pots are also low grade 1/4 watt 15 mm as well and I'm told the trannies are junk.  Lot's of cheap components for an almost $2k amp.

[PRR]

> very hissy

Do any of the knobs change the hiss? Which ones, how much?

Before heating the solder, I'd swap-out the first tube, under the can. Tubes DO go hissy. And are easier to change than resistors.

[bnwitt]

PRR,
Thank you for the response.  I'll do the the tube swap today and also verify which channel is hissy.  I noticed after I posted that the amp had it's impedance selector on 8 ohms with a 15 ohm blue alnico speaker in it as well.  I'll pull out the the signal tracer if the tube swap doesn't help and see where the hiss starts.