Sub-mini tube amps

[thomasha]

Well some new information about the amp.

I tested 4 different inductors in the max1771 SMPS, and the best result so far was with this one:
https://www.conrad.de/de/induktivitaet-geschirmt-radial-bedrahtet-1111-rastermass-5-mm-47-h-3-a-wuerth-elektronik-we-tis-7447471470-1-st-1087682.html
with 47uH, 3A and shielded, 0.074 ohms.

Compared to the others the noise is barely audible.

I changed the bias of the amp and reduced the signal going to the output stage, so it's running colder, and without the fuzz I was experiencing in the first builds.

After that, I made a video>

Now I'm working on a 3 board version U chaped, the vertical sides to the circuit, jack and potentiometers and the horizontal part to hold the tubes in place. Would help if eagle were 3D, so far I'm drawing it as an open book.

[bluescage]

Wonderful! Love it!

[Scruffie]

So I took Tomasha's ball and ran with it, a full sub-mini JCM800 to fit a 1590BB with everything but the jacks board mounted. The layout was tighter than I thought it was going to be so i'm not holding out too much hope of it working without a couple of noise or oscillation issues but you never know! So if anyone wants to try it...

Got round to building this today, the amp portion works but there's some oscillation issue I think interfering with the SMPS so it's stuck at 300V, I tried a verified standalone PCB to check it wasn't the SMPS layout and the same thing happened as soon as it was hooked up to the amp.

[Niquel]

Got round to building this today, the amp portion works but there's some oscillation issue I think interfering with the SMPS so it's stuck at 300V, I tried a verified standalone PCB to check it wasn't the SMPS layout and the same thing happened as soon as it was hooked up to the amp.

...Then it is the amp section layout?
The image showed 250V caps, so bear it in mind.
One simplistic suggestion, grounding the pots through their metal chassis. The presence circuit is ok?

[Scruffie]

I'm well aware the caps are only rated for 250V as that's what I rated them for

I gave up on it, the tubes aren't rated to run that high and after the first one blew it just wasn't worth carrying on, it was a long shot trying to get all that board mounted in a tiny enclosure and not have issues.

Everything 'worked' including the presence circuit but the amp had ultrasonic oscillation which is a layout issue and not worth fighting.

Instead i've gone for a single 6n17b JCM800 inspired preamp with a switchable cathode bypass cap instead of a tone control in to a self split power amp in a 1590B, wont be quite as high gain or sound quite the same but i'm sure for my purposes it'll be fine.

[thomasha]

Hi,
it's sad that it didn't worked, I had similar problems with my version, and that's why I reduced to 3 tubes, there was too much gain.
The thing with the SMPS is also an issue with this builds. I found a layout that works for me, but the inductor is also very important. In my last build I tested some inductors and some of them just squealed like hell.

[Niquel]

It's a pitty you couldn't fix that, the board looked so nice.
I never dared to squeeze things like you guys do.
IMHO, a 3 gain stages is too much if you try to push the power section, I prefer just one or two gain stages and some kind of transistor overdrive before.
Cheers.

[Scruffie]

Yeah it's a shame but, what ya gonna do, at least I tried and know now.

I think with a double sided board it would definitely be possible but it would be much more preferable to have an experienced tube layout-er tackle such a job rather than keep making prototypes.

It did help me see that for something where the distortion sound is the main attraction it was probably too loud for late night playing as opposed to the self split type amps which are usually just right.

I've still not had any inductor issues, I tried a couple of different ones and it made no difference whatsoever but you are also playing in much smaller enclosures with more gain than I am.

IMHO, a 3 gain stages is too much if you try to push the power section, I prefer just one or two gain stages and some kind of transistor overdrive before.

It sounds like you might prefer the new board I mentioned in my post above, if it works out i'll post up the layout for that too.

[thomasha]

Just needed to show this! It wasn't me, but could give it a try.


Really cool! check out the build log!
https://marinesnow-jp.jimdo.com/%E7%9C%9F%E7%A9%BA%E7%AE%A1%E3%83%9F%E3%83%8B%E3%82%AE%E3%82%BF%E3%83%BC%E3%82%A2%E3%83%B3%E3%83%97/submini-6021-guitar-amp/

[nzCdog]

Just needed to show this! It wasn't me, but could give it a try.
Really cool! check out the build log!
https://marinesnow-jp.jimdo.com/%E7%9C%9F%E7%A9%BA%E7%AE%A1%E3%83%9F%E3%83%8B%E3%82%AE%E3%82%BF%E3%83%BC%E3%82%A2%E3%83%B3%E3%83%97/submini-6021-guitar-amp/

Wow that's impressive

[somnif]

Who needs space anyway? 

[thomasha]

Hi, after that tiny one I had to build something.
As I wasn't hapy with the distortion that I could achieve with my superfly, I went back to a SE design.
With the extra triode stage there was enough gain on tap, and I could reduce the output volume, which allows me to play at a higher volume settings, pushing the output stage harder.

I also made a new faceplate and cage to protect the tubes.
How it was>


How it looks now>



Some extra Info>



it requires some serious offboard wiring, a 2 sided PCB would make it much easier.

cheers,
Thomas

[selfdestroyer]

I think that's my favorite one you've done Thomas. Looks great.

Cody