• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Is the KEL-84 a good Starting Point?

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I am looking into building the KEL-84 Integrated Stereo Valve Amp by World Audio Designs. Take a look here.

It looks good to me - but then I've never even heard a valve amp before...not even on a guitar!

There are two features I like the look of...

* Fail safe construction (Although I am very competent at electronics - I have a degree in it - I don't fancy being shocked with ~600V!)

* Cheap! At least for a valve amp anyway!

There is one other point...I couldn't find a single other kit available in the UK! If anyone has any comments or suggestions, I'm keen to hear them!

diyAudio Senior Member
Joined 2002

Hello Rarkov,

I don't know from the top of my head of any others in the UK apart from Maplin Electronics.
As I know most of the people at Hi-Fi World I can only give you my vote of confidence about them.
Their designs are nothing extraordinary but very good value for money.
If you don't have power hungry speakers (88dB/m approx.) and their not way below 4Ohm impedancewise I would give it a go and get some spare ECF80's while you're at it.
I can't tell for sure if these are still in production,you can still mail Nick at Hi-Fi World for that.

nice little amp, the designer seems to know what he is doing; the circuit is very similar to the origial 1949 Williamson circuit except that Wiliamson used 6SN7 and KT-66. Even the HF oscillation killer across the input pentode's anode load resistor looks similar.

I would give it a try.
Kel 84

About half a year ago I built this amp. As far as i could hear, it sounded very well. However I could hear no difference between it and my NAD 2x20 watt solid state amplifier (is this good or bad?). I have sold the amp now. Not because it didn't sound good, but because I want to build something new. It will probably be the 2A3 PSE from (again) World Audio Design.
diyAudio Senior Member
Joined 2002

The KEL-84 seems to be based pretty much on the old Dynaco ST-35 (and SCA-35). That's a darned good place to start.

And a good place to start is often a good place to improve...

The PS is my fav place, replacing electrolytics for MKP or PIO caps for starters....

There's alot of potential with the humble EL84s...

my experiences with world audio tube amp

Hi I owned a KEL34 or KEL40? Cant remember now but it was an entry level kit at around 250 - 300 Pounds. It really was quite poor and a cheap 20 year old perreaux amp remained in my system and I sold it. I do hope that some of the more expensive World audio amps are of a better quality than the one I bought, however Im afraid I wouldnt chance it. Good luck and if you try it report back, Id still like to build a tube amp that sounds good one day, my one and only attempt was very dissapointing.
diyAudio Senior Member
Joined 2002

I prefer monoblocks...so I'll have to have another look around.

So do I...but what's the difference?

If you can build monoblock GC amps, what's so difficult in doing some valved circuit?

You're an electronics student, IIRC so you may surprise the rest of your fellow students and even your teacher by coming up with some fine valved amps?

Need help? Were here.....

EL84 amps

Who said ther'es a fail-safe amp assembly ? I bet the NFB loop will howl away when you switch it on the first time or give you resistors that have 5 colour bands that can be read from both ends ? Use good soldering practice to rule out dodgy joints.

Okay, the world in my youth was full of this type of amp. It's a good start and can sound loud. This EL84 ul push pull was widespread in the early 60's record changers and tuners. You will probably find 600VAC across the secondary outers of the mains transformer connected to the anodes of the rectifier.
Use an old speaker for initial switch on should you get the NFB (output secondary the the wrong way round).
For a variation to study, I have a GEC circuit (pdf) that I could send to you direct, as the forum doesn't accept pdf format.
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