I decided to build a tube amp for the fun. In fact I think of that stuff since a really long time now (since the first amp, I ‘ve built ten years ago).

There is a lot schematics on the internet, but finding a good one is pretty hard. I want to build something like that:

Good power: 10 Watts seems to be a good starting point.
Something simple. I want to build an amp, I can fix by myself. So I decided to build a Single Ended one. (Not a push-pull) Push Pull provide far more power, but need more components and harder to build.
Low cost. The best issue for this kind on amp, is the price. You need to buy some output transformers, big power supply transformer and choke. And of course, when we talk about HIFI this cost a lot of money.
Look’s good. Something which is important is the way it looks. So I will have to take really care of that.

For people who have never seen this kind a stuff here a little pic I ripped out.

Tubes

For this design, I decided to use some EL34. Check out DrTube[0] for additionnals data. They offer good output power for a decent price.
The reflected load permits to use a KT88 instead if this doesn’t provide enought power.

For the preamp, I think I gonna use a 6SN7 in SRRP. This provide a good gain, and very good linearity.

Output transformers

EL34 has a reflected load of 2KOhm, so I need to find coresponding transformers. Of course this cost a lot of money, Hammond HIFi (not guitar) output transformer for 20w cost something like 99$ each. And
even worst, I unable to find 2.0K only 2.5 are currents.

I found this one:

EuphoniaAudio[1] (205$ the pair)
Hammond[2] (99$ each)
Electra Sud Ouest (86Euros)
Elettronocanovarria[3] (75Euros)

Despite, Elett.. offer good price, I unable to buy them here, cause the vendor speack only italian.. and that sucks. Electra sud has a good price too, so I guess I will buy them here if I don’t find anything else.

Update: I found a matched pair of 2.5K / 20W transformators on eBay.

Power Supply

This part isn’t really clear for me right now. Singled Ended amps doesn’t need regulated PSU because they work in pure class A, so the current is fixed (throught the tube bias) but It need to be really stable to avoid distortion.I don’t want to buy a large transformer because they cost a lot of money and doesn’t feet with my needs. EL34 use a quite low voltage (~250v) but need quite a bit of current ~100ma. I think, a good isolating transformer can do the job. Something like 230*230 at 200Va doesn’t cost a lot of money.

Schematic

This is really a hard part. But I found 2 good example:

first[4]
and second[5]

To be continue… ;)

Links

[0] DrTube: http://www.drtube.com/tubedata.htm
[1] Elettronocanovarria: http://www.elettronicanovarria.it
[2] Hammond: http://www.tubetown.de/ttstore/index.php/cat/c18_Hammond-SE.html
[3] EuphoniaAudio: http://euphoniaaudio.netfirms.com/ea/nfoscomm/catalog/product_info.php?products_id=28
[4] http://perso.orange.fr/michel.terrier/radiocol/detail2004/ampli-el34-se-stereo.htm
[5] http://web.mac.com/scress1958/iWeb/Steve%27s%20Tube%20Trials/EL34%20Amp.html

9 thoughts on “Build a DIY vacuum tube amp ( EL34 / KT88)”

Jkx on October 11, 2006 at 1:16 am said:

Caution Unlike said on the HackAday post, the pic isn’t my Amp, since it’s not finished yet, but this come for "Consonance". I hope mine will look that great :)
AJB2K3 on October 11, 2006 at 8:16 am said:

You seem to like these valves, cant wait to see the finished unit.
Felix Kessler on January 3, 2007 at 7:36 pm said:

Hi there… I was surfing on the net looking for some pics and I ended up here on your web site!!! You have many nice things here man!!! I work with Tube Amps here in Brazil… I also build and restore tube amps… mostly push-pull kinds like Marshall´s, Fenders, Boogie´s, etc… I just wanted to say how nice it is to read good stuff about electronics on the net… Congratulations!!! Anything you may need from Brazil or elsewhere, just let me know, ok???

Check out this TRANSFORMER producer guy… it´s the best around here… Awesome lamination!!! It´s a really great job!!!

http://www.audiolink.com.br/audiolink/transformadores.htm

It´s in portuguese… but if you click around, maybe you´ll find something of your interest!!!

Well, that´s it!!!

Keep up the nice work you´re doing and I´ll keep visiting, ok???

See yah!

FELIX KESSLER .°.
Jkx on January 3, 2007 at 10:39 pm said:

Hi Felix, I checked your website, this stuff look great. The main issue for this kind of material is the shipping cost, you know I live in France ;)

Due the weight of this transformers, I need to buy them close to my house ! :)

Bye
ruknettin on February 10, 2008 at 1:20 am said:

tube is best one…
wtube on December 4, 2008 at 4:35 am said:

Hey – the schematic for #5 you mentioned above is missing – did you happen to preserve it?
admin on December 4, 2008 at 9:44 am said:

Hum, no … some websites on this post are dead … but, stay tuned I will propose my one soon ;)
Nannra on May 31, 2009 at 2:10 pm said:

Built it very expensive and heavy
gloraglory on May 23, 2010 at 3:54 pm said:

hi,

how about you project?
is it continue?

hope you success

good work

thanks

Jkx@home

Titanium Exposé

Build a DIY vacuum tube amp ( EL34 / KT88)