Sub-mini tube amps

[thomasha]

yes,
it is really loud to play at night. I only play full gain when the volume is at 1/4 of the pot.

Unfortunately there is not much distortion at this volume level, even with gain maxed.

It works nice with pedals, but most of my pedals are bigger than the amp...

[Leevibe]

Sounds great cranked! Nice breakup

[Niquel]

Really nice amp!!
What high voltages are you using?
Regards

[jtn191]

Not exactly a sub-mini tube amp, I love the results of these designs using 12au7 as a push-pull output stage:
http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/

JTM1 http://ampgarage.com/forum/viewtopic.php?t=24671 (login to see schems)

[Hangingmonkey]

Wow, that looks really cute. I want to build one.

Edit, I'm referring to thomasha's mini jcm amp

[thomasha]

Really nice amp!!
What high voltages are you using?
Regards

The Max1771 SMPS delivers 240 v from a 12v 1A supply.

The board and schematic are here:
https://dl.dropboxusercontent.com/u/10420127/Superfly%20Project.pdf

Hope you enjoy!

[Niquel]

Really nice amp!!
What high voltages are you using?
Regards

The Max1771 SMPS delivers 240 v from a 12v 1A supply.

The board and schematic are here:
https://dl.dropboxusercontent.com/u/10420127/Superfly%20Project.pdf

Hope you enjoy!

Thanks Thomas,
What I find more intersting is the submini-combo.
I built some subminiamps, using the same schematics from Dimitry but the self-split output stage version, all of them with 6n16b and 6n17b, although I am glad with their sound, now I have bought some 6n21b to try for the preamp.
I mailed him (very kind guy) and he recommended me using any 8~10kOhm  O.T. but with this impedance, and feeding output tubes with the same SMPS than you at 220V, I was running 6n16b out of specs, so I had to lower plate voltages.
I suppose that you can use higher voltages due to the larger impedance of your O.T. Isn't it?
By the way, now I am triying to build a similar boost converter but with a cheaper UC3845 instead of the expensive MAX Ic.

Cheers

[thomasha]

Hi,
I have seen some cheaper boost converters too based on MC34063, but I still have some Max1771 for new builds. The last one I build was based on FrequencyCentral's Obsession amp:



For the JCM combo I choose the output transformer based on information from other projects, like the superfly, and I adjusted the SMPS voltage for less noise and better tone. Recently I changed the mosfet for a better one with less internal resistance,and put some 10uF 400V low ESR capacitors and reduced that value to 200 V. 

I made a document for Magnus, if you're interested it's here:
https://www.dropbox.com/s/4hcgkkefek6znqg/submini%20JCM800.pdf
It still needs some tweaking to reduce a bit of hiss at max. setting and to control gain, I always play with the gain at half, more than that and It's too much for that small speakers, they sound too distorted and have some fuzziness. With a bigger speaker it's ok.

Finished a 1590b layout, take a look:

it only has 73.4x44mm, but I'm still thinking if mounted jack's are a good approach for this build...layout was still NOT TESTED, so feel free to ask for it if You want, but there will be noise.

Cheers

[Niquel]

Thank you Thomas for all the info. I am still surprised of the primary impedance of your O.T.
I will post some pictures of my submini-amp which is enclosed in a bigger 1590DD box. I got it sounding well until I mounted  inside the box and stopped sounding so I need to do some debugging (probably a broken cable).
My idea is to build a small cabinet with a 6" 12W Jensen speaker as well, but it will take more time as I cannot fill my home with sawdust. I will keep this updated.
Cheers

[thomasha]

Very Nice Niquel!
I also build a not so small cabinet with the 6" Jensen, I made it big enough for a 8" speaker if I change my mind in the future.

As I said, I have no idea of the ideal impedance of these tubes, I just took the information available and made some experimentation.
Recently I tried a 4 ohms speaker on the 8 ohms tap, so it would result in 11k approximately, but there was a perceptible volume drop, so I'm guessing that 22.5k is better than 11k.

Are you using the hammond 125A? Could you experiment with some other impedance configurations and see what happens? Mine transformer has only the 22.5k tap.
Good luck with your build!

[Niquel]

Hi again,
The transformer I use is a 'custom made' model by a local 'trannymaker' it has 8k75 at primary and 4-8 at secondary, 2,5W.
At the moment I am using a 2x12 Celestion Vintage30 cabinet at 8 Ohms and I can say there is very low hum and enough power to annoy my neighbours.
The idea is to build the amp as an aluminium head, with everything inside the box to keep it enough portable to bring it in the guitar cover.
I built its power stage prototype, the schematic is from Dimitry's web page, in a can box of I don't know what, but it is funny because the brand says SOVIET... I forgot to switch it off for two nights and their days and it was still cool enough. When I'll finish the current version I hope I'll be able to make enough holes on its box surface to keep it cool enough as well  ...Then there'll be the nightmare of finding a good painting.
Cheers,
Miquel

[thomasha]

Well,
if you plug the 8 ohm speaker in the 4 ohm tap you will have 17k5, you could give it a try if you want.
I'm gonna try the 4 ohm speaker again and see if it really get's louder.

it's nice that yours stays cool, because mine, with 4 tubes, and specially the 6n17b, is really hot, even the guitar plug is hot after a hour playing.
But I blame the layout, the combo is very small, made of wood, and the tubes are upside down, inside of it, so not great for convection, maybe I need to add a fan.
The head is the best Idea, heat goes up and not into te chassis, and a metal one is even better to maintain things cool.

Does your boost converter uses the mosfet grounded? Because the Max1771 SMPS has a 0R1 resistance between the mosfet and ground, so it needs a special heat sink. In the 555 version the mosfet goes directly to ground, so it can be bolt directly to the enclosure. The mosfet in mine is also really hot, so I put a small heatsink on it, but it's outside the main chassis. To the 1590b version I still need to change that...

Cheers!

[madbean]

it's only taken...four years to finally get around to this? We getting close.

[culturejam]

Finally!!! 

I'm as giddy as a school girl.

[cooder]

Lookin' snazzy....!!!