VOX AC15 project?

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VOX AC15 project?

Postby add4 » 12 Sep 2012, 09:45

Hello,

So i tried a vox AC15C1 yesterday and ... i liked the normal channed and LOVED the top boost channel....

I'm wondering if i could combine that, and my interest in learning to build tube amps (building the madamp J5 kit at the moment, no other experience in amps, made 30 or so pedals).
In fact, i thought about it because i heard that vox amps are basically super simple, but the tremolo section makes it complicated... and i'm not interested in the tremolo so it soudns like a potentially easy build, am i right?

What i would like : vox ac 15 normal and top boost channels, no tremolo. Ideally in a smaller, more portable and lightweight cabinet.

my questions:
- I looked for ac15 kits online, but i couldn't find any, would you happen to know one?
- if there is no kit, is there a project with an existing layout ? (i know i could follow an existing layout, buy parts from sellers, make my own BOM, etc.. but i'm not experienced in laying out components point to point, and i've heard that the routing of cables plays a major role in hum and tone.... and i know nothing about it too ... )

Possible issues i have in mind:
- Historically, the top boost was not in the AC15, so i guess taking an old schematic and removing the tremolo wouldn't work.
- Historically, the tremolo channel is a second channel, would removing it change the tone of the amp (one friend has a 1 channel deluxe reverb which saturates waaaay too early, the builder says it's because he omitted the normal channel, and the existing channel has too much power ... i thought tubes werre powered and drain whatever power they needed, but whatever.. )
- I found a schematic of the top boost channel only, it seems it could be added to any existing vox schematic, is it that simple?
- Removing the tremolo channel would free up a few tubes, the top boost uses one half of a preamp tube, how many tubes would i need?
- i read that the EF86 tubes are problematic .. if the amp works correctly, it's only a matter of trying a few and find the ones that are not microphonic, right? how is that a problem? i already select my preamp tubes now because theres so much difference between two tubes...

Any information/link/help is appreciated.
Thanks in advance.
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Re: VOX AC15 project?

Postby add4 » 12 Sep 2012, 10:36

I just read that the tremolo section changes the sound of the normal channel ... do you have informations about that?
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Re: VOX AC15 project?

Postby devastator » 12 Sep 2012, 12:45

the vox ac15 is it the one with the pentode tube ?

A kit isn't necessary if you know where to buy your part (and what parts you need) , few web shops offer that service. The fact is that you can select the component technology that you like the most. For the layout it must certainly exist on site like "Ceriatone" (I even think I got one for the ac15 ) but making one isn't that hard , just a little work and understanding how a turrent board is designed (really not a big deal ) .

the lead dress is important yes, but here again, not a big deal if you do it right (and even some big compagny amps aren't clean on this point by the way)

- Historically, the top boost was not in the AC15, so i guess taking an old schematic and removing the tremolo wouldn't work.
- Historically, the tremolo channel is a second channel, would removing it change the tone of the amp (one friend has a 1 channel deluxe reverb which saturates waaaay too early, the builder says it's because he omitted the normal channel, and the existing channel has too much power ...


"Historically" you don't care, if you want to build your own amp you shouldn't have to consider that kind of things. If you want to combine channels and ideas , just do it ! (IMHO that's pointless to make clones or replicas )

i read that the EF86 tubes are problematic .. if the amp works correctly, it's only a matter of trying a few and find the ones that are not microphonic, right? how is that a problem? i already select my preamp tubes now because theres so much difference between two tubes...


Not really a probleme I guess, Just a bad design.

Removing the tremolo channel would free up a few tubes, the top boost uses one half of a preamp tube, how many tubes would i need?


triodes are two in one valve , pentode are alone. I let you do the math. You can remove the tremolo section if you don't want it.

I recommend you to read that site to clear up things :

http://www.freewebs.com/valvewizard/index.html
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Re: VOX AC15 project?

Postby roseblood11 » 12 Sep 2012, 20:58

The modern AC15C1 has the simple 12ax7-based normal channel, as the AC30. I think the EF-86 based channel of older AC15's is much more interesting. And that one has been combined with the AC30's top boost channel in the older "Heritage Collection" series, both with 30W and 15W power amp. I use an AC15H1TV from that series, it's a great sounding amp and the combination of these two channels in one amp is really useful, Vox should have done that decades ago. But that amp has two issues:
a) the decoupling of both channels isn't perfect. If you plug into the EF-86 channel, the controls of the top boost channel still change the sound a bit
b) the wiring is a complete mess: http://img38.imageshack.us/img38/4145/img0867n.jpg

You can find the servive manual for the AC15H1TV with schematic and complete layout plan here:
http://forum.zelfbouwaudio.nl/viewtopic ... t=ac15htvh

Maybe I'll rebuild the circuit on turretboard someday and replace the complete wiring. The rest of the amp is relatively (china...) well-made. The new amps have a much better build quality inside, but the combination of channels is much more interesting in the heritage collection models.
http://www.youtube.com/watch?v=BRZfeYxgsgI

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Re: VOX AC15 project?

Postby roseblood11 » 12 Sep 2012, 21:15

EDIT: I just read that there is a new Heritage Series AC15 with both EF-86 and top boost channels. Does anybody have the schematic or servive manual for that one? Or maybe a gutshot?
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Re: VOX AC15 project?

Postby darkbluemurder » 13 Sep 2012, 16:57

I would consider buying an 18 watt kit. The chassis is drilled for 3 preamp tubes and 2 EL84 output tubes and a 6X4 (EZ81) rectifier. That would give you a normal channel (with one half 12AX7) and a top boost channel (this needs one and a half 12AX7s). Even the pot and jack locations are at convenient places. If you can read schematics it should not be a big hurdle to adapt a Take your time getting the layout right. A good place to check layouts is Ceriatone, even though I don't think that they would have the exact amp you have in mind.

Good luck,
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Re: VOX AC15 project?

Postby Ripdivot » 13 Sep 2012, 18:08

I have two AC15C1 amps and I love them. I also have interaction between the two channels. If I play through the top boost channel with the master all the way up so I am clean, the "normal channel volume" control acts like a bass control. I think it actually helps. If you play dirty with the master down and the pre vol up the normal channel volume doesn't have this same effect. Doesn't matter to me because I really like the amps. By the way the one in the store just up the street from me reacts the same way.
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Re: VOX AC15 project?

Postby roseblood11 » 14 Sep 2012, 22:48

It's no problem as long as you only use one channel in a live situation. But I'd like to switch between them with an external A/B switch... I'll see if I can find a solution. I think that the way how both channels are connected to the phase inverter is not ideal. See schematic: http://forum.zelfbouwaudio.nl/download/ ... 37c134a55f


A great addition to any Vox amp is a post phase inverter master volume, as described here ("Variante 3"):
http://www.unet.univie.ac.at/~a9525719/amp/index.html

Here someone built a clone of the AC15H1TV: http://www.tube-town.de/ttforum/index.p ... 010.0.html
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Re: VOX AC15 project?

Postby joeboo88 » 14 Sep 2012, 23:27

add4 wrote:.

my questions:
- I looked for ac15 kits online, but i couldn't find any, would you happen to know one?
- if there is no kit, is there a project with an existing layout ? (i know i could follow an existing layout, buy parts from sellers, make my own BOM, etc.. but i'm not experienced in laying out components point to point, and i've heard that the routing of cables plays a major role in hum and tone.... and i know nothing about it too ... )

Hi, Add4:
I was considering building an AC15 type amp and have found a few things, mostly the cost as i am cheap. :mrgreen:
I did find a good website that has something like you are asking about
http://www.trinityamps.com/Product_Trin15.htm
There are layouts for this i found here:
http://www.trinityamps.com/ForumGallery ... Doc_Files/
They also have a forum where you can learn about what your building.
http://www.trinityamps.com/phpbb/index.php

I didnt build the TC15 though i built trinity's "trinity 15" which is like the lightning.
I like it and it sounds really nice. I didnt buy the kit just built it from the schematic/layout. It doesnt have a top boost, but the TC15 does.
Yesterday i just finished my tweed deluxe, different animal! and i love this thing! i built for about $200.00 (my father-in-law gave me the tubes, so that saved me about a $100.00) :mrgreen:

I still have enough parts left and am probably going to either build an 18watt plexi type (which i should have instead of the 15, but thats me.)
or viewtopic.php?f=2&t=13635 from one of our brothers here at this site...this thing looks interesting...
High volatges building these kinds of things, watch out, good luck!
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Re: VOX AC15 project?

Postby rcustoms » 15 Sep 2012, 01:49

A more comprehensive layout schematic with a point to point connection
Vox.pdf

enjoy
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Re: VOX AC15 project?

Postby DougH » 25 Sep 2012, 17:28

The "problematic-ness" of the EF86 was because they built the amp as a combo and it was picking up vibration from the speaker, making it oscillate. Build it as a head, and if you have problems don't put the head on the speaker cabinet. I built a 10W version of an AC15 as a head and have never had one iota of a problem with the "microphonic" EF86.
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Re: VOX AC15 project?

Postby wyatt » 26 Sep 2012, 03:06

joeboo88 wrote:
I didnt build the TC15 though i built trinity's "trinity 15" which is like the lightning.
I like it and it sounds really nice. I didnt buy the kit just built it from the schematic/layout. It doesnt have a top boost, but the TC15 does.
Yesterday i just finished my tweed deluxe, different animal! and i love this thing! i built for about $200.00 (my father-in-law gave me the tubes, so that saved me about a $100.00) :mrgreen:


The Lightning preamp is a Top Boost preamp.

The Matchless C-30 is nothing but Vox circuits with heavier filtering. The 12AX7 channel/Lightning preamp is Vox Top Boost preamp based. The EF86 is '58 Vox AC15 preamp based. The OP can take that and rework it as a 15-watt amp, but Trinity already did that, the aforementioned Trinity TC15....
http://www.trinityamps.com/Product_Trin15.htm
http://www.trinityamps.com/ForumGallery ... _18Dec.jpg
http://www.trinityamps.com/ForumGallery ... 5Oct07.jpg

All the OP has to do is drop the filtering to Vox levels (replace 32uF caps with 16uF caps and 20uF caps with 16uF or 8uF caps); change to Vox dropping resistor values; and calculate the PT needed to get Vox voltages. The OP should be able to print out the TC15 schematic, mark up the cap and resistor values and be set inside of 10 minutes. Make sure to use the choke instead of the first 1K5 dropping resistor.

BTW, this will also get some DAMN close to a 15-watt Z-Wreck on the 12AX7 channel. A Z-Wreck is little more than a Trainwreck Rocket with a vintage Vox filter cap values, vintage Vox dropping resistor values, and Vox dropping resistor parallel routing (already used on the TC15); and the Trainwreck Rocket was little more than a Vox AC30 scaled back to just the Top Boost preamp and the poweramp (with heavier filtering, different plate voltages, and series dropping resistor routing).
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Re: VOX AC15 project?

Postby Vendt » 26 Sep 2012, 07:14

Hi just saw this thread for the first time.

I've build exactly what you are thinking of. An AC15 with 12AX7's no tremelo and no vibrato and channelmixing.
Channel mixing is done by adjusting the volume of the channels.

I've used a Marshall 1974 kit. As we've build this in a course in ampbuilding we've had 2 different kits a TAD and a Weber.
Both of them had their pro's and con's.

http://www.tubeampdoctor.com/en/shop_AM ... Combo_3444

To change the schematic is not so hard to get an AC 15 a couple of cap switches a few different wirings and you're set.
It sounds like a VOX....and is pretty versatile.

I'm having some problems with my version, but that has most likely nothing to do with the schematic.

If you'd like to know more, let me know!
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Re: VOX AC15 project?

Postby dellamorte » 26 Sep 2012, 09:16

have a look here Image
i have one and they are great , you can get all the parts from nik or a kit.
they are highly recommended and easy to build ( mine was a first amp project)
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Re: VOX AC15 project?

Postby DougH » 26 Sep 2012, 19:00

Hammond makes replacement transformers and chokes for Marshall, Vox, and Fender that are reasonably priced, too. I got one of their Marshall replacement transformers and I am happy with it. Check them out if you need a power transformer or etc that is spec'ed for a Vox.

Edit: Also, mojotone is a good source for Heyboer FenMarVox replacement iron. I got a replacement power xformer for my Marshall Artist from them and it works great. Much more reasonable than the pricey Mercury stuff, and very good quality too.
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Re: VOX AC15 project?

Postby uncleboko » 27 Sep 2012, 21:10

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Re: VOX AC15 project?

Postby roseblood11 » 27 Sep 2012, 21:44

add4 wrote:I just read that the tremolo section changes the sound of the normal channel ... do you have informations about that?


this question is still open...
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Re: VOX AC15 project?

Postby wyatt » 27 Sep 2012, 22:34

roseblood11 wrote:
add4 wrote:I just read that the tremolo section changes the sound of the normal channel ... do you have informations about that?


this question is still open...


Probably. Ultimately any change made to a tube amp alters everything else, they are rather reactive that way.

Yet I don't see anyone going out of their way to recreate the AC15 pentode- or triode-based trem channels...neither on a Matchless nor a Vox model (or any other boutique spin of the AC15). In this case, the point seems moot, the OP isn't looking to build an exact clone of a '58-'60 AC15 anyway, just adding the Top Boost channel will have *some* effect on the Normal channel. One can't sweat authenticity when hot rodding a classic.
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Re: VOX AC15 project?

Postby roseblood11 » 01 Jan 2018, 22:45

Old thread, but...

My idea of a perfect and simple "modernized" AC15 would be: EF86 normal channel with 6-way tone switch, Top Boost channel and the bias tremolo from the pacemaker for both channels.
Has anybody build an amp like that?
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