DIY Valve Guitar Amp Head

[DrNomis_44]

Hey Doc, I built this AX84 Hi-Octane Tube Guitar Amplifier some years back. It's a great sounding little amp. The wiring was easy but making the chassis etc was really the time consuming part and I had access to a pretty good workshop for the sheet metal etc. We had a laser cutter and made the front and rear decals. note that it does go up to 11.....

Attachment 14425
I made a cover for the power transformer on a 3D printer as well.

Attachment 14426
Rear View

Attachment 14427

If anyone wants to build one I can add more photos on the inside.

That looks really cool, yes, the AX84 website has lots of great amp projects to build, there's a wealth of good info on that site and I have visited it quite a few times in the past, definitely one I could recommend adding to your bookmarks list.


Here's a link to the AX84 website for those who want to check it out, be sure to bookmark it if you find it interesting enough:


http://www.ax84.com/

[Marcel]

I had a look at the AX84 site and despite there being some good stuff there I wasn't overly impressed.

My preferred site is http://schematicheaven.net/

From schematic heaven I devised my own hybrid of a JTM45 and 2204/4104 circuits plus a few of my own tweaks to build my own point to point wired 50W head.

There were a few obstacles to overcome, and changes due the re-use of the power and output transformers from the 6L6 based Playmaster (Electronics Australia) head that it was in a past life, but it has a new life now feeding a pair of Celestions the good vibes emanating from all my guitar builds...

I still have a few changes planned for it such as a post phase inverter master volume and some tweaks to the tone stack to name but two. It all fun, and it feels so good to have the knowledge that I built the whole lot from guitar go to sweet loud noises WHOA!!

[DrNomis_44]

I had a look at the AX84 site and despite there being some good stuff there I wasn't overly impressed.

My preferred site is http://schematicheaven.net/

From schematic heaven I devised my own hybrid of a JTM45 and 2204/4104 circuits plus a few of my own tweaks to build my own point to point wired 50W head.

There were a few obstacles to overcome, and changes due the re-use of the power and output transformers from the 6L6 based Playmaster (Electronics Australia) head that it was in a past life, but it has a new life now feeding a pair of Celestions the good vibes emanating from all my guitar builds...

I still have a few changes planned for it such as a post phase inverter master volume and some tweaks to the tone stack to name but two. It all fun, and it feels so good to have the knowledge that I built the whole lot from guitar go to sweet loud noises WHOA!!

Wow, that's a nice little amp you have there mate, so how does it sound?

[Marcel]

For a single channel amp and in one word....AWESOME !!

I have it in my shed where I do all my guitar builds and that is about 40m from the house (I live on acreage) and only once have I cranked the master up to 5, whereupon the wife complained that she had to turn the TV up because of my "noise"... noise that was IMHO clean, crisp and sharp... If I wind up the pre-amp gain it brings on quite a reasonable crunch right through to a half decent dirty.

It can't be as dirty as my standard JVM210C, nor match it on volume, but it does have its own character/tone which I put down as mostly being the ported speaker cabinet that I also built and the Celestion's the cab is loaded with.

It's certainly a more than an ideal 'workshop amp'...lol

[Marcel]

While I pondered on the colour progression of my ES-1TL build I took the time to have a play in my favourite stomping ground ad fitted the post phase inverter volume control to my home made 50W (Master volume type 2103/2104/2203/2204) clone. refer http://schematicheaven.net/marshall.html under the series 'JMP 1959 Lead 50W' for the pdf circuit this is based upon.

If you look closely at the differences from this photo and the earlier photo you can see the dual gang 250k pot on the back panel that is the heart of the mod. In the bias circuit that feeds the EL34's there are (in Marshall designs) a pair of 220k resistors feeding the bias voltage to the output tube grids. The mod basically turns these two resistors into a variable volume control. Zero volume essentially connects the grids direct to the bias supply point, and 100% volume has the same effect as if the pot wasn't there. The Eagle eyed among you will notice that there are still 1M resistors going from the bias 2nd filter cap and the grid current limit resistors which are there to ensure there is always bias on the grids even if the post inverter volume pot has momentary open circuit moments when adjusted, and have the secondary effect of pulling the 250k pots back to 215k which is close enough to 220k as to not be bothered about.

I also added a 0.1uF across the high voltage supply to V1. This has the effect of reducing some of the noise that the cascaded stages in V1 are prone to make. The low input only uses half of V1, whereas the High input adds an extra 10dB of gain from the other half of the tube but sadly also adds to the noise floor. The cap helps to reduce the noise of the extra stage. It's getting better and I'm happy with it, but I know more can be done...

How does it sound?.... Clean on the low channel with flat EQ is wonderful with crisp bright highs and full lows . And with SD hot rails into the high channel I am left wondering why I ever spent money on OD pedals... and the wonderful thing is with the post phase inverter volume modification I can now wind it all down to evening bedroom volume levels or wind it up to ACDC concert levels without changing any of the drive through the three 12AX7's who do most of the work in creating a 'Grunge' or a 'Dirty' sound...

Now I need to work out a way of doing an 'effects loop', and a 'record line out'....

[Zandit75]

While I pondered on the colour progression of my ES-1TL build I took the time to have a play in my favourite stomping ground ad fitted the post phase inverter volume control to my home made 50W (Master volume type 2103/2104/2203/2204) clone. refer http://schematicheaven.net/marshall.html under the series 'JMP 1959 Lead 50W' for the pdf circuit this is based upon.

If you look closely at the differences from this photo and the earlier photo you can see the dual gang 250k pot on the back panel that is the heart of the mod. In the bias circuit that feeds the EL34's there are (in Marshall designs) a pair of 220k resistors feeding the bias voltage to the output tube grids. The mod basically turns these two resistors into a variable volume control. Zero volume essentially connects the grids direct to the bias supply point, and 100% volume has the same effect as if the pot wasn't there. The Eagle eyed among you will notice that there are still 1M resistors going from the bias 2nd filter cap and the grid current limit resistors which are there to ensure there is always bias on the grids even if the post inverter volume pot has momentary open circuit moments when adjusted, and have the secondary effect of pulling the 250k pots back to 215k which is close enough to 220k as to not be bothered about.

I also added a 0.1uF across the high voltage supply to V1. This has the effect of reducing some of the noise that the cascaded stages in V1 are prone to make. The low input only uses half of V1, whereas the High input adds an extra 10dB of gain from the other half of the tube but sadly also adds to the noise floor. The cap helps to reduce the noise of the extra stage. It's getting better and I'm happy with it, but I know more can be done...

How does it sound?.... Clean on the low channel with flat EQ is wonderful with crisp bright highs and full lows . And with SD hot rails into the high channel I am left wondering why I ever spent money on OD pedals... and the wonderful thing is with the post phase inverter volume modification I can now wind it all down to evening bedroom volume levels or wind it up to ACDC concert levels without changing any of the drive through the three 12AX7's who do most of the work in creating a 'Grunge' or a 'Dirty' sound...

Now I need to work out a way of doing an 'effects loop', and a 'record line out'....

[Marcel]

LOL...!

Ask... and I'll answer... :-)

[Guvna19]

Wow Marcel, That wiring is as good as I've seen, Looks Sweet as ! (whilst admitting my amateurish knowledge and total lack of experience)

Sadly , I have to accept the safe wiring skills required for such a project are currently beyond me

I have been lookin at valve amps for the last 2 months DIY / KIT /Schematics / speakers /cabs / new / 2nd hand. cant stop....lol

I dont really need a new amp or guitar ,and attempting to justify to the missus otherwise still needs further refining.

Seems obvious thats not your first amp build, What was your first build?

regards
Guv

[Marcel]

Well Guv.... Thanks for the compliment, but to my eyes it still looks a bit like a dogs breakfast yet everything is there for a reason and a purpose. So you do realise the picture here, I'm 55 and I first started in electronics when I was just a cub in my early teens so there is just a little experience in there too ...;-)

If memory serves me rightly, my first actual amp... was back in the early '70's in my early years of High school, a 10+10W stereo amp to to go with my vinyl record player so I could play the newly released Deep Purple and 'Frampton Comes Alive' LP's that I had just acquired... Electronics Australia magazine (which is no longer in circulation) had published a circuit, and I convinced my dad to get me the parts from Radio Parts (RPG) on Spencer St. in Melbourne and what I couldn't get there I got from a new upstart company called Dick Smith which I think back then was on Elizabeth St in the CBD. By the time I finished year 10 in '77 I had built many things one of which was my own 8bit CPU computer in a laptop attaché case which I used to control my brothers train set and all the learning made my subsequent formal electronics training in the RAAF a relative breeze easy experience.

If you are new to it or anything Gav... my suggestion is to start small, and when you have repeated success then get more adventurous. Aside from building electric guitars from PBG there is Jaycar who have a few interesting and useful cheap kits for musical/guitar projects to help learn basic electronics with...

As for mains powered kits and tube amp builds, I strongly suggest getting at least some formal training, particularly in regard to electrical safety and the high voltages that are found in tube circuits. Without the training it is all too easy to develop bad practices which will ultimately result in tragedy... And nobody wants tragedy.

Too Many people dismiss it but electrical safety is a big concern. I do hold a fully endorsed restricted electrical licence (NREL) that I studied for through TAFE. It is worth the effort. It also means I know my amp is safe yet I also know I could never sell my amp due to its one glaring failure, and I think few here could pick what that failure is...

[DrNomis_44]

That's the same approach I took to learning Electronics, I started off with the simple circuits and when I felt that I understood how they worked, I progressed onto more complex circuits, same with actually building them.