Sub-mini tube amps

[thomasha]

That's a nice Board!

[Niquel]

Madbean:My boards look much more shabby!

Thomasha: I haven't used any heat sink that's what surprised me, I have to see what happens with the max1771 smps...but I have enough room inside the case if I need any.
I repaired many 'big' combos with tubes downward mounted and almost all of them had marks of heat in their pcb's if these were above tubes, there's a model I remember, a Crate Vintage Club that had this heating issue in their pots, but I have to admit that your whole amp looks very nice, I would try a fan, as you mentioned.
Cheers,
Miquel

[thomasha]

The first month after my build I played with the amp without the heat sink and I was experiencing a change in tone after playing some time. With the multimeter I saw that when the amp was really hot the high voltage dropped from 220 to 190 V. With the heat sink the amp became more stable, and there is a lower voltage drop.

I'm waiting to see a little more from your boards! They look amazing!
Cheers
Thomas

[Niquel]

Hi all,

I've been working a little on the 3 submini tubes and max1771 smps head, now it sounds quite good but I have the same issue than you, Thomas: hiss at max. gain and max. volume. I like its tone specially for ac-dc, led-zepp rocks.
I need more holes on its top to cool it (about 50ºC after 30') and have to do some tests recording to find changes in tone due to heating, but I´d like to keep its psu without heat sink, if possible. I'll test it with the 4Ohms output as well to listen its changes.
The 2x6n16b, with a NE555, will stay as it is, I know it can cope with its temperature and it has been my test rig for months without issues.
There are some pictures of the 2x6n16b and 2x6n16b+6n17b model.
Cheers,
Miquel

[thomasha]

Nice builds, make some gut shots from the second one, if possible,
I would like to see how you managed to squeeze everything inside the box.
And a sound sample.
The hiss doesn't bother me, as I newer play mine at full volume, normally only at something between 1/4 and 1/2 of the total volume.
I also bought some 6112 to compare with the 6n17b. I read somewhere that the russian subminiature are cleaner sounding when compared to the american, to make my Superfly crunch I had to use 220k anode resistors with a cold and a hot biased stage.
I'm waiting for some components to start my new board and test it.
Cheers

[Niquel]

Hi Thomas,
Sorry, I can not take any pictures right now, but I hope I will have some time one of these day, I'd like to profit when I open the amp to fix the hiss issue, make some more holes and take some temperature readings.
At the moment, I can show you the preamp section I have used, is from a JCM800 series, but I don't know which one.
The power stage is the same schematic as on previous post.
The layout is the same idea as the other amp, but it has two PCB's for pots: gain, vol, sweep and tone stack at the other. All linked by screened cables.   
I like the sweep pot, as it moves all the bands, it is quite useful to change the whole amp tone for different styles.
I also would appreciate suggestions for paintings. I already have some synthetic solvent based painting in spray but last time I used it, it did not last so long, so I am thinking in some primer.
...Whel, that's all for now.
Cheers,
Miquel

[thomasha]

Hi,
reusing a marshall schematic was a good idea, it looks very nice also.

Never tried that sweep pot, maybe on the next build...

To your painting I would say:
a lot of fine sanding (600 to 1200), than paint it 3 times with the primer and wait until it's dry,
after that 3 to 5 times of the spray painting. You can use a hair dryer to make the painting/waiting steps faster,
but be careful to not overheat it, otherwise it will produce small bubbles.
Cheers,
Thomas

[m-Kresol]

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

Woohoo! Since I only started 3/4 of a year ago it hasn't been to long for me but I can't wait to get rid of my solid state Fender amp I've got since I started playing years ago... definitely looks most awesome to me. Looking forward to this!

[thomasha]

Hi you all,
After some reading I started calculating the best configuration for the 6N16B output stage.

A friend from another forum, Matec, ploted the load lines for the 6N16B tube using the Paint KIT V2 from here:http://www.dmitrynizh.com/tubeparams_image.htm

For 150V and 180V a 22k transformer was used, while for 200V a 34k, and for 230V a 44k transformer.
As the images show, the 180V 22k configuration runs the tube with a 0.8W dissipation to output 0.75W.
In this configuration a lot of heat is produced, and the tube's life is reduced. Matec suggested to use de 44k configuration, that has an output of almost 1W with a 0.7W plate dissipation.
To bias the amp at 9.1VDC the 1.2k cathode resistor will now be 2.2k, as 2*2.1mA*2.2k=9.24V.

To achieve this, i'm going to use the 4 ohms tap of my 22.5k transformer with a 8 ohms speaker, and change the SMPS trimpot to output 230V.
With the increase in voltage and impedance there is a decrease in plate dissipation, current consumption and an increase in output volume.
If you guys are using the russian subminiature tubes like I do, this small change will make the amplifier louder and cooler!

The same graph also shows the power stage sensibility as 9.1V or 6.4V rms, this will be usefull to make a better PI.

I also read some articles about layout in SMPS:
http://ecee.colorado.edu/~ecen5797/course_material/layout.pdf
http://cds.linear.com/docs/en/application-note/an136f.pdf
And changed the SMPS to a separate ground, and reduced critical areas:


Before building this amp I will recalculate each stage to the best configuration!
Cheers
Thomas

[Niquel]

Hi all you,
Nice piece of work, Thomasha.
I have been working on the submini head on its ground scheme to remove hums and other noises and finally achieved a quiet amp.
As shown on picture at previous post #100, I have replaced the 1K5 R8 (cathode resistor in output stage) for a 2K2, reducing power dissipation from 0,99W to 0,7W, as I have now B+1=210V and Vk=7,72V. I have an impedance ratio of 8750:8 in my O.T. and tested with the 8750:4 and an 8ohm speaker too, to double its Zpri. but readings didn't changed much.
It would be nice to test it with a hammond 125A transformer with other impedances to see if it really increases output power with higher impedances.
Find below some gutshots and the 6" jensen speaker cabinet.
Cheers.

[thomasha]

Hello,
great build! Good to hear that you solved the noise issues!
I'm still waiting for my parts to test the new layout.
How is it sounding to you with the new cathode resistor and higher/lower impedance?
Cheers

[Niquel]

Hi again, Thomas and others, and thanks.
I would say it had more "character" before, but it was just noticeable when I turned up the volume pot. The thing is that, for practising at home, I have enough volume with gain at some point, depending on what I am going to play, and volume control between minimum and first quarter. The first stage draws so much, that you can play with the volume pot all the way down but then, tone stack is useless.
I hope one of this days will get a mic. and time to record some sound samples, painting the box and covering the cabinet with tolex. I don't know where I can get some corners for a so small cab.
Your design is very interesting, although I would prefer a separate SMPS from main board, just because if PSU starts smoking you just have to replace it and if you have ground noises you can find a solution moving a single (or maybe more) cable(s) as I did. But obviously, if everything goes right you'll have a design much more compact.
Good luck and tell us your findings .
Cheers.

[mishagolin]

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

Brian, Could you give a brief overview of the amps you've created?

I know you were designing them with charge pump power supplies but what about the other design aspects

Are these mainly 6111, 6112, 6021 tube styles?
Push-Pull or single ended?
Hammond 125 output tranny for push pull? Hammond 1750 for single ended?
Will they have a headphone output option (bypass the power amp section)?

I'm really looking for a small headphone amp i can build that is a preamp section off of a tube guitar amp. I can try to mock it up myself but my etching abilities suck. I was considering buying your PCB and then just populating the preamp section and pushing that straight to an output without the tube power amp or output tranny.

Misha

[mishagolin]

Well, after murder one I tried to build my own tube amp combo...
based on jcm800 amplifier, using russian submini tubes, with PP triodes and LTP PI.
I used Dmitry's power amp schematic, and made a PTP layout using nails as turrets.
The speakers are old oval computer speakers, and I used a big muff tonestack instead of the TMB.
The power supply is the max1771 SMPS, from frequency central projects, and a 12V, 2A wall wart.
I made some videos with my crappy phone cam:

Beautiful work Thomas. I was thinking of taking this route. Do you think the sound would be greatly improved if you switched the last tube from the 6n16b dual triode to two power pentodes? I'd imagine since the EL34 is a pentode that something like the 5902 would sound closer to the real thing, just quieter.

i think any beam power amplifier might give you a better power amp section.

[thomasha]

Hi,
I also believe that the pentode would be an improvement, and using the 5902 is exactly what Dana made here:
http://ampgarage.com/forum/viewtopic.php?t=6159&start=0&postdays=0&postorder=asc&highlight=submini

edit: Nice would be use low voltage subminiatures, like the 5672 and a low voltage triode, with max. 100V, to make a small and low dc amp. These 1W amps are quite too loud to play at home....
cheers
Thomas