Hi,


does anyone have knowledge of mono tube preamps without semiconductors and transistors?

Years ago someone mentioned building a few in a japanese magazine (don't remember the name)

I remember one picture of a (very) small metal box with a single tube.


Does it sound feasible?



Johnsy.

 

There is a stomp box like that. I don't remember the name. I'll ask my son later today.

Try this...
http://www.instructables.com/files/orig/FBS/QWA4/GPBDFWOL/FBSQWA4GPBDFWOL.pdf

 

Try this...

Thanks a lot! this is a nice introduction to tubes.

There is a stomp box like that.

If you get the name that would be great.

I just want to add that one of the preamp in the magazine was listed as "tube preamp mono MIC" by the author.

Most mono tube preamp are tube boosters - overdrive, distortion effects which was not the case of the author preamps.

 

I think I can achieve the same thing with a FET and a 9V battery.

 

I'm sure but it wouldn't glow!


I'm well aware of the solid states vs vacuum tubes debate but as i have access to a selection of tubes it might be a good afternoon project.

So if anyone as a schematic (or informations) on (small) tube mono preamp (mic), this will be greatly appreciated!

 

you might want to search "glowbugs" for tube projects.

 

Hello,

You might want to have a look at the "old books online" site:
http://www.tubebooks.org/technical_books_online.htm

There is a section for hifi tube amplifier books.

Bertus

 

What kind of tube amp were you looking for?
Something to drive a speaker?

 

I'm sure but it wouldn't glow!
...

So you need a FET, a 9v battery and a LED!

 

Nah, RB. Use the FET amp, but replace the LED with a tube to keep the punters happy.

 

you might want to search "glowbugs" for tube projects.

Thanks, didn't know this (it brings up a lot of very interesting pages)

You might want to have a look at the "old books online" site:

Thank you! what a find, browsing through this is gonna take some time!

What kind of tube amp were you looking for?
Something to drive a speaker?

A single tube mono preamp, Yes.

I guessed that choosing a mono mic preamp instead of stereo would have been be a nice introduction to the world of vacuum tubes , but strangely it proves more complex than i thought.

So you need a FET, a 9v battery and a LED!

Alright but where is the warmth? not led size but doesn't take much space:

"Sub-miniature tubes"

 

Well as an introduction to tube amps.
A single tube will probably not have enough gain to drive a speaker from a microphone. Also a transformer is needed at the plate of the tube to match its impedance to the speaker.
Tubes require a higher voltage than most modern electronics and another power source to heat the filaments.The EZ81 tube can be replaced by a 1N4007 diode to simplify things if you wish. The dual control is just a tone control.
A well stocked junk box of older parts may be needed.

Here is the source of of this schematichttp://www.angelfire.com/vt/audio/

 

Hello,

The following projects may also interest you:
http://www.pmillett.com/micpre.htm
http://diyaudioprojects.com/Tubes/12AX7_Preamp/

Also the following page has a lot of schematics:
http://www.kbapps.com/audio/TubeGuitarAmpDesigns.php

Bertus

 

Thanks for the schematic and link!

A single tube will probably not have enough gain to drive a speaker from a microphone.

Not too sure about that one, more details on this can be found in the "Vacuum Tube theory & circuit design" section of TBO (thanks again bertus!)

To be able to fit everything in a small enclosure i might have to look for a hybrid amp (the transformer is an issue and will also require a separate enclosure)

Even if i don't have sub-miniatures tubes, i'll look into the schematics (and size)

At this size transformer(s) are not an issue!

The following projects may also interest you:

Once again thanks a lot bertus!

I think that with all that i got everything, i will check the tubes i have for specs and if i have premium tubes in the collection!

It looks more like a weekend (or even a week) project, than an afternoon!

 

For those also interested by the subject (but a bit overwhelmed) i found this page with a lot of details (but clearly presented) including a list of preamp tubes, which help!

About sub-miniature vacuum tubes in particular:

The cheap k261 valve preamplifier kit from oatley is worth looking into.