Choosing a 1/2 Watt Tube Amp!

[PedroTejada]

Hi!

I'm researching about tube amps for some time. Past year I started a 100Watts SLO project, but I stopped it, since my band stopped playing and it was too much for my bedroom.

Now I'm switching my working area to my dad's office basement and I don't want to put my Roland amp there (Not really safe to leave expensive stuff out there), so I'm planning to make a 1/2 watt tube amp and plug it into my 1x12' cabinet.

So far I found 4 1/2 watt projects:

- The Murder One by Rick (FrequencyCentral): http://www.diystompboxes.com/smfforum/index.php?topic=73222
- The JJS Class A Amp: http://www.jjs.at/electronic/class_a_subminiature.html
- The SuperFly also by Rick (FrequencyCentral): http://www.diystompboxes.com/smfforum/index.php?topic=78302.0
- The Z.Vex NanoHead: http://www.freestompboxes.org/viewtopic.php?f=2&t=511&p=91562&hilit=zvex#p91562

I have the PCB for two of them, and I'm working on one for the Murder One. The Nano head project uses a PTP board, something that I really like!

My main question is: Anyone had experiences with those amps? The tubes they use? How they sounded live and in the studio... Any tips?

The second question is: Most of those projects are supplied by a 9V source and voltage raiser ICs. There are any advantages in using a transformer (like the nano head)?

I'm open to any suggestions! This week I'll try to test my friends Nano Head (Lucky that he have one! It's probably the only one in Brazil  ).

Thanks,
Pedro 

[petemoore]

  they all look good to me.
 power supply, output transformer, other 'firsty thirsty' things, the JJs and Ricks amp look to have well thought through power supplies, I didn't examine the Nano.
 Then the tubes, I have a 6SN7 amp, clean preamp, haven't tried a submini amp yet, looks like a nice future amp build.
 Speaker db ratings can make the amp way less volume, as well as offering an alternate sound, low db rating may be 'stubborn' to drive and offer other attractive features.
 So a larger extension cabinet with effecient speaker[s could make it a jammer-amp, pull the ext. plug, plug in the small cab/low volume speaker and have a night-room amp.

[frequencycentral]

I've got two of those! I've built a few dozen Murder One, it works reliably every time, the power upverter is simple yet effective. I've built two Superfly, louder than Murder One, but much harder to get the power upverter right, just the right parts are needed, it's not very forgiving.

The link to the Nano doesn't work of course, this one will if you remove the spaces:  

http://  free  stomp  boxes.org/viewtopic.php?f=2&t=511&p=91562&hilit=zvex#p91562  

The Nano schematic is not complete, as it doesn't include the SMPS section, a P/T having been used instead. But maybe sometime Zack will share his design?

There are certainly advantages to using a transformer instead of an upverter, I've been looking at this one recently: http://www.tube-town.net/ttstore/product_info.php/info/p2358_TT-Powertrafo-EI-230---200---6-3-7-VA.html  .....which would be perfect for a submini amp build. While not as small as an upverter based amp, a P/T would seem to negate the difficulties is fine tuning a SMPS - which sometimes seems more like magic to me than electronics!

[davent]

Something else you might want to consider is building a larger amp and then powerscaling it so you can dial it back to  1/2w output or even less. London Power sell various kits for this, or Hall Amplification sell the VVR kit but you could also roll your own. Lots of info on diy VVR at Sewatt. You need to register to see the info but that's no big deal.  http://www.sewatt.com/node/16248

dave

[Ronsonic]

I built a cigar box guitar amp awhile back. Used one 12DW7 tube and a Fender reverb driver transformer. I forget the details, but very basic. The 12DW7 is a dual triode one half equivalent to a 12AX7 the other a 12AU7. Low gain half is connected to the transformer and the high gain as a very basic gain amp. I used a standard high voltage supply. In the end it didn't have quite enough gain for my taste, but loved all pedals.

If I go to build another such amp it will be two tubes a 12AX7 for gain and drive and an output maybe 6SN7 or 12AU7.

[svstee]

Check out Sopht amps too.
http://www.sophtamps.ca/mambo/index.php?option=com_content&task=view&id=25&Itemid=37

[sean k]

My first was the moonlight which may or maynot still be somewhere on the ax84 website.

P/P 6SN7 output, 6SL7 phase inverter and a EF183 pentode as voltage amp. Very nice through a 4 x 12"

P/P's are less power hungry, and therefore more efficient, than an SE but most of the above, and the moonlight are triode outputs and you may be looking for low wattage pentode out's in which case maybe a P/P 6AK6 amp with 6AV6 (1/2 a 12AX7) and 6AU6's as voltage amps.