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Old 23rd March 2009, 06:09 PM   #1
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Default A few questions from a total novice.

Hi, i am a total novice with regards to building amps and i was hoping to get some advice here for a project i am interested in doing.

Bascially my idea is as follows. I'd like to make a low-medium power, single channel guitar amp based on the Vox EF86 preamp channel, with one or two EL84's for the output stage. As i understand it single ended designs are somewhat simpler to build than push pull, so i would probably go down down that route.

Here is what i am looking for in terms of controls. Master volume, some kind of simple blilliance control (either a pot or a 2 position switch for flat/bright), pentode/triode selector switch for the EF86 and a simple switch to lower the gain on the input jack (-6db or so).

Can anyone advise me on how difficult this kind of setup would be? Being a total novice i will obviously need help with a layout and some step by step guidance for the build. But if i can find someone to help me with these things, would the project be do-able or would it still be far too complicated for someone like myself?

I have good woodworking skills from building guitars for a number of years, so the cabinet etc.. will be no problem for me. I am reasonably handy with a soldering iron too, but my experience only goes as far as guitar/bass wiring.

Thanks in advance for any help! (and apologies if my question is too vague/naive)
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Old 23rd March 2009, 08:16 PM   #2
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Check this out:

http://www.instructables.com/id/Guitar-Tube-Amp/

The project amp uses different tubes, but may be helpful anyway.

Jeff
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Old 23rd March 2009, 08:48 PM   #3
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Default Re: A few questions from a total novice.

Quote:
Originally posted by bonescan
Can anyone advise me on how difficult this kind of setup would be? Being a total novice i will obviously need help with a layout and some step by step guidance for the build. But if i can find someone to help me with these things, would the project be do-able or would it still be far too complicated for someone like myself?
A single ended guitar amp is a very wise choice for a novice and very achievable. I myself am working on one right now which is similar, 1 channel is 6J32P (like a Russian EF86), 1 channel is 6N2P (like a Russian 12AX7), and the power tube is a single "super 6BG6GA". I am building it on perfboard, which I love, but is generally not popular with the tube crowd. More common for guitar amps is turretboard or point-to-point.

You can do a little searching to get some ideas. Personally, I am not too crazy about your design, I think you are underestimating the required gain a bit, but if that's intentional because you envision this as purely a home practice amp, that's cool.
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Old 24th March 2009, 12:06 AM   #4
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Default Re: Re: A few questions from a total novice.

Thankyou for the link Vinylkid58, i will take some time to look through it

Quote:
Originally posted by leadbelly


A single ended guitar amp is a very wise choice for a novice and very achievable. I myself am working on one right now which is similar, 1 channel is 6J32P (like a Russian EF86), 1 channel is 6N2P (like a Russian 12AX7), and the power tube is a single "super 6BG6GA". I am building it on perfboard, which I love, but is generally not popular with the tube crowd. More common for guitar amps is turretboard or point-to-point.

You can do a little searching to get some ideas. Personally, I am not too crazy about your design, I think you are underestimating the required gain a bit, but if that's intentional because you envision this as purely a home practice amp, that's cool.
Thanks for the encouragement, could you briefly explain what you mean by my current idea lacking gain? Just to explain the thinking behind my plan, i recently had the chance to play one of the Vox AC15 handwired amps, and i absolutely fell in love with the EF86 channel. I really don't want any heavy distortion, just some smooth breakup and high sensitivity to pick attack.

For me, the 15 watts of the Vox was more than enough - and although i don't understand how you reach the total wattage figure for a given amp, i was assuming that using a similar tube compliment i would arrive at roughly the same overall volume as the Vox. I will be using the amp mostly for home recording (if it turns out well!) and maybe some small gigs, but certainly nothing big.
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Old 24th March 2009, 01:27 AM   #5
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Default Re: Re: Re: A few questions from a total novice.

Quote:
Originally posted by bonescan
Thanks for the encouragement, could you briefly explain what you mean by my current idea lacking gain? Just to explain the thinking behind my plan, i recently had the chance to play one of the Vox AC15 handwired amps, and i absolutely fell in love with the EF86 channel. I really don't want any heavy distortion, just some smooth breakup and high sensitivity to pick attack.

For me, the 15 watts of the Vox was more than enough - and although i don't understand how you reach the total wattage figure for a given amp, i was assuming that using a similar tube compliment i would arrive at roughly the same overall volume as the Vox. I will be using the amp mostly for home recording (if it turns out well!) and maybe some small gigs, but certainly nothing big.
The tube complement of an AC15 is 1 x EF86, 3 x 12AX7, and 2 x EL84 (plus rectifier). Assuming it is close to the design of a vintage AC15, when using the EF86 channel, the EF86 drives a 12AX7 differential stage and then push pull EL84's. If you just put an EF86 driving an EL84 in SE, you will have far less gain since you are leaving out the 12AX7 stage, plus a single EL84 output will only get you a maximum 3-4 watts theoretically.
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Old 24th March 2009, 04:32 AM   #6
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Default Re: Re: Re: Re: A few questions from a total novice.

Quote:
Originally posted by leadbelly


The tube complement of an AC15 is 1 x EF86, 3 x 12AX7, and 2 x EL84 (plus rectifier). Assuming it is close to the design of a vintage AC15, when using the EF86 channel, the EF86 drives a 12AX7 differential stage and then push pull EL84's. If you just put an EF86 driving an EL84 in SE, you will have far less gain since you are leaving out the 12AX7 stage, plus a single EL84 output will only get you a maximum 3-4 watts theoretically.

Aha thanks for the explanation, i was under the impression that the AC15 was SE, and that the EF86 channel only used that single tube for the preamp stage (i wrongly assumed the 12AX7's were used for the Top Boost channel only).

So to recreate the EF86 channel reasonably accurately i will need to use 1 x EF86 - 3 x 12AX7 - 1 x EZ81, is that right? Also how many EL84's in SE configuration would be needed to get to the same ballpark in terms of volume of the AC15? Would i run into any issues that might complicate things if i wanted to run say 4x EL84's SE?
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Old 24th March 2009, 04:56 AM   #7
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Vox schematics here.

Jeff
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Old 24th March 2009, 05:03 AM   #8
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Default Re: Re: Re: Re: Re: A few questions from a total novice.

Quote:
Originally posted by bonescan
So to recreate the EF86 channel reasonably accurately i will need to use 1 x EF86 - 3 x 12AX7 - 1 x EZ81, is that right? Also how many EL84's in SE configuration would be needed to get to the same ballpark in terms of volume of the AC15? Would i run into any issues that might complicate things if i wanted to run say 4x EL84's SE?
If you're that set on partially cloning the AC15, then just google a vintage AC15 schematic and "cut out" the 2nd channel, and just ground the grid of the bottom triode where the 2nd channel fed in. So, you'll need 1 x EF86, 1 x 12AX7, 2 x EL84 in push pull, 1 x EZ81. It makes no sense to go 4 EL84's in single ended, it'll be more difficult to build and won't sound like an AC15.
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Old 24th March 2009, 04:16 PM   #9
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Default Re: Re: Re: Re: Re: Re: A few questions from a total novice.

Quote:
Originally posted by vinylkid58
Vox schematics here.

Jeff
Thankyou! that's great.

Quote:
Originally posted by leadbelly


If you're that set on partially cloning the AC15, then just google a vintage AC15 schematic and "cut out" the 2nd channel, and just ground the grid of the bottom triode where the 2nd channel fed in. So, you'll need 1 x EF86, 1 x 12AX7, 2 x EL84 in push pull, 1 x EZ81. It makes no sense to go 4 EL84's in single ended, it'll be more difficult to build and won't sound like an AC15.
Ok thanks very much. The reason i want to partially clone the AC15 to start with, is that i know i love the sound it makes. Since this is my very first attempt at building any kind of amp i figure this is the safest option, then when i have finished i can play around with different component values to see if i can change it even more to my liking.

Anyway thanks a lot for your patience, i guess it's time for me to do some reading now and learn the basic principals of what's going on at every stage of the EF86 channel.

Then i'll come back with even more annoying questions on how to build the thing
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Old 24th March 2009, 05:15 PM   #10
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Default Re: Re: Re: Re: Re: Re: Re: A few questions from a total novice.

Quote:
Originally posted by bonescan
The reason i want to partially clone the AC15 to start with, is that i know i love the sound it makes. Since this is my very first attempt at building any kind of amp i figure this is the safest option, then when i have finished i can play around with different component values to see if i can change it even more to my liking.
Very wise choice. Classic guitar amps are a safe bet; their sound had to be popular for them to become classics. Let me know if you need more help in figuring out how to modify the AC15 design for what you want to do. You should also think about construction technique.
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