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Old 15th September 2011, 12:03 AM   #1
diyAudio Member
Join Date: Sep 2011
Red face Vox AC15 project

Hello everybody,

Really new to this, just registed, and french, so sorry for my writting mistakes i do the same in french...
I started thinking about the amp of my dreams and realised that it doesn't exist !!
So, why not trying to make it myself !?!

I would have like a kind of VOX AC15HTVH1 head, but with the look of the Night Train ( for the box i can make it myself , that's not the probleme). With a spring reverb, like the AC30, no need of tremolo and vibrato, no real need of top boost, but i'd love to have a 2 mode switch on 1 jack; a EF86 mode with pentode-triode switch, and the bright levels like the AC15HTVH1, and an another mode with the classic bright channel from AC30, withe bass-tre-hig level and a kind of switch bright - thick like the night train so 2 x 12AX7 (one would be enough ?).
I'm a real pure novice but quite curious and trying to have a no-limite state of mind about what human can learn to do when we enjoy it !! And hopefully friends of mine are really good about DIY on ther electronic parts and have the good material and tools for it (optimist but not dumb). But
But one good thing about internet is that you can learn and read a lot of informations in a few time ! So, if i have a bit understood the many shematics that i have seen, if i want a spring reverb i need another 12AX7 in the prťamp part, just before the amp part, maybe with just a blend selection.
For the amp part it will be two EL84, that i would like to switch from pentode to triode (for indoor unsing ang high gain sound in low level).
What do you think about a line out and headphone jack (with level) just before the EL84, will the EF86 sound "VOX enough" if i plug it for an outdoor show where the 15w would not have been enough? I know that it won't be the same but would it be stupid to try it ?
I read that the EZ81rectifier is good part of the VOX sound, so, let's go for it too!
2 output for cabs in8 ohm
For the speakers, i will make the cab as small as possible (if it doesn't change the sound ?) and depending of my budget a Celestion Blue Alnico 12" 15W-8ohm, a WGS Black&Blue or a Celestion Greenback inside . But i prefere to keep the 15W, looks to sound really better.

As you can read i already make my mind about some element of the project and i don't know if it will be possible.

My bigest question is about the power transf, the output transf and the choke, can i use the models you can find on DIY stores or does my "options" need another model, and where can i buy them ????????????????????????????????????????????

No shems for the moment, i started thining about this project when i read this forum http://www.diyaudio.com/forums/tubes...mp-layout.html.

Thank for your awnser , pleeeease !!!!
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Old 15th September 2011, 06:54 AM   #2
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Join Date: Nov 2010
Location: England Hertfordshire
all sounds very possible but a bit too much for a first time build maybe? anyway you seem set on doing this so:

In most DIY stores transformers go up to about 50v so i wouldnt suggest that. im not sure of the best place to get them from france, but theres edcore and hammond transformers available in a few places.
as for only using 1 12 ax7, for exactly what you want im not sure it will be enough, although 1 12ax7 will be enough when you use the EF86. and if you want any distortion, you wont get alot from 2 gain stages unless you oush the amp pretty hard. sounds like youd also want to cathode bias your EL84's as its supposed to give a warmer sound, but i think in some amps vox used a mixture of fixed and cathode bias. pentode/triode switching is doable, just need to connect G2 to the plate of the pentode, you can put a 100 ohm resistor there to be safe.

as for headphone and line out, you might want a bit of EQ and filtering there as your not getting any effect from the frequency response of the speaker. and with a headphone out, youl have to mute the amp, you cant unplug the load. (at least i think so, im not too up on headphones)

as for volume outside 15w should be plenty but it might not have too much clean headroom. youl get quite a bit of crunch at full volume, but then again for what you have in mind it might be fine, it is very loud after all.

For the cab, everything affects how it sounds, size, stability, wood, open/closed back etc.

Good luck
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Old 15th September 2011, 06:56 AM   #3
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Location: England Hertfordshire
By the way i think this should be moved to instruments and amps
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Old 15th September 2011, 07:24 AM   #4
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Default how ?

Hello, thanks for your really quick awnser !! How can i move this to amp and instruments? I'm new to this.

Ok, si i'll keep for the preamp 1 channel EF86 and the other channel 2x12AX7, and after that one more 12AX7 for the reverb, better?

for the transformer and choke, i've seen that hammond got a large choice of models, once i'll have my shems ready to be post, maybe i'll need help to choose it depending of the final layout configuration...

Thanks for the pentode-triode information, i'll keep in mind.

In fact, i'm looking for the warmer vox sound as possible, so i'll set the EL84 as you told me. No real need of big disto, a little bit of crunch why not but not too much, that would be nice to be able to pump the volume without having too much distortion...

Thanks for your awnser, if u see anything else i need to know before starting...

For the tube i read that at a good price the JJ models are often good one, any other suggestion ?

Thanks !!!
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Old 15th September 2011, 07:43 AM   #5
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I've moved to Instruments and Amps

You can use the report post button to request this sort of thing. little red ! in a triangle in the bottom left of the post.

Any intelligence I may appear to have is purely artificial!
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Old 15th September 2011, 07:58 AM   #6
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thanks !! I'll know for latter...
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Old 15th September 2011, 12:15 PM   #7
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Originally Posted by dabitsusan View Post

Ok, si i'll keep for the preamp 1 channel EF86 and the other channel 2x12AX7, and after that one more 12AX7 for the reverb, better?
Phase splitter? you need one more ECC83 for that.
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Old 15th September 2011, 12:26 PM   #8
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what do you mean by phase splitter ? if i need i'll add one tube more, ok ? but why ?
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Old 15th September 2011, 08:18 PM   #9
taj is offline taj  Canada
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Originally Posted by dabitsusan View Post
what do you mean by phase splitter ? if i need i'll add one tube more, ok ? but why ?
You have some reading to do (okay, a lot of reading). Every tube has a purpose.


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Old 15th September 2011, 08:45 PM   #10
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK

A "real pure novice" is best off leaving design well alone, and building a kit,
or finding a broken valve guitar amplifier with lots of info available and
fixing it / restoring it.

On your own there are far too many mistakes you can make, and contrary
to your opinion, there is as much misinformation on the web as there is
real infromation. The simplest is usually wrong / not right for the case.

No way should a novice attempt a full amplifier, it will go wrong.
It will oscillate most probably, and you will suddenly find you need
to know everything about valve guitar amplifiers to build a good one.
I don't, see below.

Buy a working used valve guitar amplifier and refurbish / tweak it.
It will be far cheaper, safer, and more rewarding in the long run.

rgds, sreten.

I bought this used in excellent condition for far less than the parts would cost :
Click the image to open in full size.
15W, classic 10" H|H british Invader speaker, classic spring reverb.
No building grief. Haven't touched it, because there is nothing wrong with it.
If it ever starts to go wrong, then I'll fix it, not really interested in modding it.
It simply works, and works very well, build quality is way beyond a homebuild.

Last edited by sreten; 15th September 2011 at 09:12 PM.
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