[Niteshade]

I was curious as to whether any school projects involved tube amplifiers or if children are getting into tube technology on their own. Basic amplifiers are easy to build and it is possible to use some tubes withotu excessive voltages. It's sad that companies like Heathkit are no longer around- but it's not too difficult to find everything you need these days over the internet.

[MaxCast]

How about an AC tube amp project 
We all build along to completion.

[Niteshade]

When you say an AC tube project- are you referring to those that are powered directly from the AC mains like AC/DC radios?

[rklein]

Blair, Blair, Blair...  you are too funny   I think what MaxCast is referring to by the statement 

How about an AC tube amp project

is Audio Circle members do a tube amp project which I think would be very cool.

Yours,
rklein

[MaxCast]

Oops, didn't realize this was the JR audiophile circle.  But yeah, a simple project that any member could build along.

[Niteshade]

Oh! I get it! I'd like some young folks input in it too. My 5th grade science fair project was a dual output DC power supply that was running a dc motor and radio at the same time. A small tube amp project won't be that much more difficult.

One of the big issues is typically noise reduction with tube amps. The best way to avoid this problem is to make a push-pull amplifier since they naturally reduce allot of power supply noise. The easiest tubes to wire are octal ones (larger contacts) and that's important for people new to soldering. I have a link to a phase splitterless push-pull design on another computer and will post that tomorrow.

[Niteshade]

Here is the schematic I promised:

http://diyparadise.com/simpleel84.html

Push-Pull w/out phase splitter El84 Amplifier

[S Clark]

Blair,
We have had some first year physics students that built some amps from kits that Gary Dodd provided.  However, Gary sent the prototype, and the kids simply copied it.  By the end of the year, kids are capable of reading reasonably simple schematics, and I think it would make for a better learning experience if we built from schematics.  So your offer of a schematic is a nice addition.
Thanks,
Scott

[Niteshade]

I would recommend using either 6V6 or 6L6 tubes in place of the EL84's since octal socket tubes are easier to solder to. Use a 6SN7 in place of a 12A__ series driver tube. Putting together a kit is a great way to start.  In 'The Lab' circle you'll find where I put up a thread that has 25 tips for beginner DIY'ers.

Make sure you get a power transformer capable of at least 6 amps for filament current and around 200ma for the HV supply. I don't like undersized power transformers.

Let me know if you need anything else.

Blair

[planet10]

This spud amp is pretty easy...

http://t-linespeakers.org/tubes/SEP_50EH5.html

dave

[BradJudy]

Perhaps low voltage tubes would be best for high school students.  A good option would be Pete Millett's "starving student hybrid" headphone amp - http://www.pmillett.com/starving.htm  It's designed to be simple and inexpensive, a very accessible build. 

The only downside is that the gain is pretty high, so it isn't a good amp for using with easy to drive things like iPod earbuds. 

[Niteshade]

Keeping the HV down is a good idea. A 6L6 and 6V6 will operate at 240v without a problem. They operate cool when loaded properly as well. If a line isolator is used, the HV can be used directly from the isolator via a voltage doubler circuit, then all that's required is a $11.00 filament transformer from Radio Shack. (12.6vct @ 3 amps).

There's allot to learn from building a tube amp. Learning how to be innovative is just as important as any other trade skill.

[Ericus Rex]

Sounds like a cool project even for NON-junior audiophiles, like myself!  Are you thinking of making the original version or the updated version?

[Niteshade]

If you're referring to the basic vs the more complex version, it's best to try the basic version without the additional gain stage and use a cathode resistor instead of the diode. If you choose to make this using 6L6's, then the extra gain stage is necessary and some component values will have to be changed.

Sounds like a cool project even for NON-junior audiophiles, like myself!  Are you thinking of making the original version or the updated version?

[Ericus Rex]

Any interest in getting some people together to perhaps get a bulk discount on some parts for this thing?  Anyone?

[S Clark]

I might be interested in a buy if I have enough students that want to build an amp.  I'll contact the local physics teachers next week to see if there is interest.

[Se7en]

I'd be into this 

[Niteshade]

I almost forgot about this topic! 

Another idea came to mind: A basic 6V6 single ended amplifier. They're easy to assemble and the parts will not cost too much. On top of this- several interesting things can be tried with it:

1. A Choke filter
2. Effects of negative feedback
3. DC vs. Cathode biasing
4. Tube Rectifier vs. SS diodes

Since there isn't much wiring involved and pentodes are easy to get along with- an amplifier project like this can go in phases by adding in the above mentioned circuits. Above all else comes the troubleshooting exercises in hum elimination. Single ended amps can be touchy when it comes to hum and finding ways to deal with it is a project in itself.

[Mr Content]

My 13 yr old son has expressed interest in doing this. I hope it gets of the ground, as he will be in.

Mr C aa