OT: lxh2 low power EL84 tube amp

[slajeune]

Hi All,

anybody build one of these things?  There was some talk in the archives about this but no build reports...

http://home3.netcarrier.com/~lxh2/lowpsch.html

Anybody have a clearer schematic (ascii, arrrgh...)?  Any hints on actual power supplies that could be used with this?  What would be a replacement for the TL080?

This is very intersting stuff....

Stephane.

[idlefaction]

the TL0xx family have a pretty easy to remember code - the first 'x' is either 6, 7 or 8, and the last 'x' is the number of opamps in the chip.  for the first 'x', 6 means low current consumption, 7 means general-purpose, and i forget exactly why but 8 means really high sound quality but high current consumption.

so a TL084 is a 4-opamp, high current consumption, high quality chip.

as for the rest, you may as well build a valve amp    if you're going to use a small output transformer, it will probably have no bass anyway, and if you're going to get a large output transformer, you're well out of stompbox territory.

honestly, just build a 18W marshall or a matchless spitfire!  
http://www.ax84.com/
http://www.ampage.org/

[slajeune]

Hi Daren,

I do agree that building a full valve amp is desired but:

- I want a very low volume (db) amp
- I want to stay away from lethal voltage

This is why this design seems to accomplish what I am looking for.  I do agree that this doesn't relate (and is very far from a stompbox).  I was just trying to see if anybody had success with this design.

Thanks,
Stephane.

[slajeune]

I think that I found the proper power supply / transformer for this project:

http://www.tubesandmore.com/new/scripts/silverware.exe/moreinfo@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?item=P-T166N12

If anybody has any other pointers, that would be greatly appreciated.

Edit:

If I understand correctly, the heaters on the EL84 are the ones that require a lot of current (.76A each).  If I connect them in parallel, this requires 1.52A (6.3V).  But, if I connect them in series (12.6V) it only requires .76A, right?  If so, a single 12VDC 1.5A should suffice for the lxh2, right?

Thanks,
Stephane.

[puretube]

cc. TLxx : 6x = lo consumption
              7x = lo noise
              8x = g.p.
or so I was told...

[slajeune]

Thanks for the info puretube.  Do you have any information pertaining to putting DC current on filaments (heaters)?  I was thinking of trying to hookup the LXH2 on a 12V DC 1.5A Wall plug.

Thanks,
Stephane.

[Peter Snowberg]

The heater requirement is 0.76A @ 6.3 volts. If you run both heaters in series and power that with 12.6V, it leaves about 9 watts of supply capacity with your 1.5A supply. This assumes that you have a regulated 12.6 volt supply. If unregulated, your milage will vary.

Take care,
-Peter

PS: if you want an excellent source of tube data, download this: http://www.duncanamps.com/tdslpe/download.html
While at Duncan's site, also be sure to pick up his tone stack calculator and send him a donation for his hard work if you can.

[slajeune]

Hi Peter,

thanks for the info!!!!  It is interesting to know that I can power this sucker with a simple 12VDC power supply.  This makes it a bit easier to try this project out.

I will definately try the project and I will post the results when I have time to build it.

Thanks!
Stephane.

[puretube]

12V DC on the heaters in seriesis is perfectly OK (i.e. only 5% off the suggested 12.6V);
don`t ask me what I think about a B+ being about  230 to 300V off the suggested B+ for EL84s...

and, although not being a hi-power-freak,
10 to 30 mW is not that much...


...but it is a nice thing to get acquianted with the vacuum...

[slajeune]

Hi All,

I have spiced the schema and it does seem to work.  I don't have the right spice model for the output transformer and therefore the output isn't perfect.  But, the design does seem to work.  There are two mistakes in the schematic.  With the first two non inverting opamp stages, a polar cap needs to be added to the feedback loop.  Failure to do this will produce very strange audio waves!

I have ordered everything and will probably build it in the next few weeks.

Once the build is finished, I will post an updated schema with the corrections and also post some pictures of the beast!

Thanks for everybody's help!

Stephane.