My first foray into DIY valve electronics a.k.a adventures with a Velleman K-8020

[James]

Be careful about attempting to measure resistance and continuity 'in circuit', as the various components (even capacitors) can give you a false reading (esp if using a digital meter).

Aye, that's why I unsoldered all components on any given track to eliminate their influence. Last night's and tonight's effort netted me two (!!) track errors. Despite showing see thru clarity of light between tracks, they were (according to my DMM) shorting to ground. The one I found tonight was easily fixed by running the small sharp blade of my Swiss Army knife between the tracks to get rid of any microscopic (they'd have to be ... I couldn't bloody see them) remains of unetched copper.

Well, that fixed the problem. Hurray!!!

I've just finished a two hour listening session, and I remain gob-smacked how such a simple circuit with a triode for each channel can make such sublime music. Whilst I had my Densen preamp in for repairs, I borrowed an Audio Research LS16 mk2 to tide me over for a week. I could easily hear the appeal of valves. The ARC had a richness of tone and timbre that instantly grabbed my attention, but my interest faded soon after when it was clearly let down by the muted dynamics and laid back presentation. Reminded me too much of early day Musical Fidelity.

At USD300 (plus postage), the K8020 promises more, and indeed it delivered. The signature timbral richness was obvious, but this time I didn't fall asleep. The infectious rhythm of Tommy Castro kept me well pinned to my seat. It might not have the crystalline purity of my B-250, but I could easily live with the way it makes music. Alex S was right, the K8020 is a very special preamp, assembly hiccups notwithstanding. Highly recommended for anyone who'd like their first foray into valve preamplification without breaking the bank.

James

 

[Alex S]

Hi James,

Welcome to cheap valve world. Sorry you were unlucky with the building side (Alan Clarke built a pair without a hitch, so I wouldn't let this put people off). Its a really good little preamp, especially for the money. The power amp is even better and so little worse than the HX1.2 (my favourite SS amp) as not to matter, especially at a tenth the price.

Anyway, how do I change the valves.....?

 

[James]

Welcome to cheap valve world. Sorry you were unlucky with the building side (Alan Clarke built a pair without a hitch, so I wouldn't let this put people off). Its a really good little preamp, especially for the money. The power amp is even better and so little worse than the HX1.2 (my favourite SS amp) as not to matter, especially at a tenth the price.

Hi Alex, and thanks. The trouble was well worth it. Which power amp are you referring to?

Anyway, how do I change the valves.....?

Did you not get my PM? Just in case not, you just need to undo the top two screws on the front and back panels with the allen key. The case is in two parts, and you simply lift the top half clear.

Here is a view of mine showing how the case is split asymmetrically.

James

 

[Alex S]

No PM but no matter - now I see the construction its easy.

The power amp is the Velleman K4040 - 90W of 8 x EL34; should be able to drive your speakers easily enough. The Vellemans in combination have the makings of a tidy system, and a great second one.

 

[Patrick Dixon]

Last night's and tonight's effort netted me two (!!) track errors. Despite showing see thru clarity of light between tracks, they were (according to my DMM) shorting to ground. The one I found tonight was easily fixed by running the small sharp blade of my Swiss Army knife between the tracks to get rid of any microscopic (they'd have to be ... I couldn't bloody see them) remains of unetched copper.

Well, that fixed the problem. Hurray!!!

You can get these kind of 'invisible' track shorts, and that's why most production manufacturing uses bare board testing (BBT) to check pcbs. I should complain to Vellemann so that they can beat-up their pcb manufacturers and make you suitable recompense.

Very well done for sorting them out though - should give that warm glow of satisfaction to all the music.

I'm still awaiting news from Alex's 'contact' for my Vellemann kit, and a replacement mains transformer for the BP power amp. Things move slowly in valve world ... ;-)

 

[Mr Tibbs]

Good work, James.

It's a pity about those annoying PCB faults. I'm sure they're not the norm and I would take Patrick's advice and get onto Velleman about it - a spare PCB would be handy for building a modified version...

Mr Tibbs

 

[James]

I should complain to Vellemann so that they can beat-up their pcb manufacturers and make you suitable recompense.

... a spare PCB would be handy for building a modified version

Yes, that's a good idea. I quite fancy another K8020 kit to build the modified version.

Things move slowly in valve world ... ;-)

You don't say. But like fine wine and cheeses, these things take time.

James

 

[fran]

I remember seeing some of these velleman kits for sale in Maplins - but at what I thought at the time to be outrageous cost. I can't find the kit now, but you can still see the power and output transformers.

Heres the Q - are these transformers any good? £20 for a power xformer and 24 for an output transformer with 4,8 and 16R taps, says its suitable for 2 x EL34 valves.

The reason I'm asking is that I'm planning on building a valve amp in the fairly near future and am trying to accumulate some parts over time - would these be a good buy or would I be better off buying somewhere else (and where?)

Fran