DIY Integrated Valve Amplifier?

Having successfully (after a few minor problems) built my DIY valve phono stage I've caught the DIY audio bug. So now I'm giving serious thought to building a valve amp. So does anyone have an suggestions for designs/kits I should have a look at? One concern I do have is whether I'll be able to drive my Quad 11L's with a valve amp, as I was under the impression that you need fairly efficient speakers.

Cheers,
BL21DE3

 

welcome to the wonderful world of valves

once bitten, forever smitten!

for kits:
www.hificollective.co.uk
www.diyhifisupply.com
www.worldaudiodesign.co.uk (I think, do a search if stuck).

Penance had some joy with a foreign one too, but I cant remember its details for the life of me.

as to which type of valve amp would suit you, first defining factor is price.

Id personally go with a WAD amp for budget to mid range, and for single ended stuff hificollective.. only not doing the diyhifisupply because you get better UK support with the other 2.

I know people who will fix it if you bodge it, or just want it made for you - let me know (they will charge of course).

On the power thing, dont worry overly. a 20w valve amp will sound like 100w solid state in most cases.

If not doing just for fun of making, it might be worth looking for ads, often you can get pre-built kits second hand for good prices...

Chris

 

my first valve amp was based on the mullard 5/20,5 valves (ok so mine olny had 4 cause it had a solid state psu)and 20 watts output,sound wise very nice,maplins still stock both the transformers. my current amps include a pair ofthese plenty of power at 90w

 

Cheers for the links/suggestions guys. After my success with a complete DIY job, admittedly based on a well documented circuit, the idea of a complete DIY build appeals more to me than buying something preassembled. I came across a modified variant of the 5-20, called the 4-30 based around Lundahl transformers which looks quite interesting. themadhippy, just out of interest which transformers at Maplins would be suitable for the 5-20? Anyway, I think I'll have to do a lot more research to find a design that is reasonably cheap but offers a decent sound.

 

At 700 ish I would reccomend the single ended integrated from hificollective. I dont think you'll find a better amp for the money. Its gpt a passive volume control, hard wired with no circuit boards and a decent transformer. It looks great too.

At 300 ish, the entry level WAD kit using EL84's provides sound far beyond its price point.

Dont forget that when you've chosen your kit you often have the option of paying more and swapping some of the resistors/caps etc for something a bit better, and changing the stock valves for better quality ones.

Chris

 

dont seem to be able post a direct link but the part numbers are DM54J and DM53H

 

themadhippy, cheers for the part no.s. Bottleneck, the hificollective amps are a little out of my price range at the moment, though they do look rather good. The Kel84 does look fairly nice, and pretty good value when you consider what buying the individual parts would cost you. As for upgrading/improving parts, that is one of the things that appeals to me about valve equipment. Though to be honest if I did go for a kit I'd probably get it in stock configuration so I could get used to the basic sound and then base my modifications upon that. I'll just have to do my homework and work out whether I can justify buying/building a full valve amp when I'm more than happy with my RA-02 and it's just the DIYer/tweaker in me that wants a new project .

 

knew they were on my hard drive somewere,
the maplins millenium circuit diagram

and another version of the mullard 20

 

Cheers for the schematics. My father has lent me his copy of 'High Fidelity Sound Reproduction' which has the schematics for the 5-10 and it's companion pre-amp amongst others. And I also discovered that the schematics for the 4-30 also contained the original 5-20 schematics. Just out of interest, where did you source the 90W mono amp kits and how much were they?

 

i got the kits from maplins,(code vt60,now discontinued)cost £350 eac ,that dosnt inclue any case though,they also do them as a stereo kit including case for £699(vf83e).The diffrence between the 2 is the stereo amp uses a single power supply

 

hmm bl21de3 you're looking at watts again arent you dude?!

I once borrowed an 80w per channel pair of KEL80 monoblocks from WAD, and man they were beasts. I was nervous round the volume control.

My rough (very rough, very dependant) rule of thumb is multiply your valve amps power (rated in watts) by at least 3 times and you'll have the solid state equivelant.

I know this is hard to believe, but its just true! someone like hippy can give you the reasons why, but Im not technical in that way...

 

themadhippy, cheers for the info on the kits.
bottleneck, having done some more reading/browsing I now realise that the power ratings for valve amps can't be directly compared with solid state ratings. The Kel84 is starting to look very tempting, though I'm having difficulty trying to justify changing amps just for the sake of satisfying my DIY urges. I think I might investigate building a pair of 5-20 based monoblocks and using the RA-02 as a preamp/backup amplifier.

 

thats not a bad idea.

Should you turn out to prefer the valve power stage, you can always look at getting/making a passive or valve pre to go with the power amp, using the money from the Rotel to finance?

Or of course if you go for a valve integrated kit you can directly compare with the rotel and sell one on.

'sure you've already thought of all that though!
Chris

 

Cheers for the comments. The 4-30 monoblocks idea looks like it's bitten the dust as by my rough calculations I'd be looking at £400+ before I'd even bought the cases or valves. So it looks like I'll need to consider either a single DIY 5-20 based unit with the RA-02 as a pre or a Kel84 kit. Though to be honest I'm more inclined to go with the kit to save on the hassle of tracking parts down etc. I'll just have to give it a bit more thought and see if I want to take the plunge.

 

I drew that! Where you get that from?

It's not even the original Maplin cct anyway, this is ~ with my latest 'improvements':

 

I was part of project build of a 6SN7 and KT88 power tube amp build called Son of Heffa.
It operates in a non compromising form, gets warm, uses juice and has silicon power reg that is particularly good - dead quiet on the scope.
Details of my build and circuit etc can be found here.
http://home-and-garden.webshots.com/album/535523301vfXSDn

One of the co designers later wrote this wiki
http://en.wikipedia.org/wiki/Valve_audio_amplifier_-_technical#Biasing

I reckon it cost about £350 all up back in 2002. I have used it and used it and used it and used it God knows how many hours?! It's needed a little tweaking over the years. A few resistors were underspec'd, the heat sinks not big enough. I found rewiring the signal path & speaker out with solid core oxy free copper to be good.
The mains transformer is a big beast and is the heart of the amp.

It started out as an integrated with a simple potential dividing pot. Then I discovered TVC's (all about impedence matching) and now I am on more efficient speakers and have by-passed the 1st tube stage of the amp to attenuate by about 21dB. This means the TVC is much less strangling (I run it at perhaps -12bD instead of -48 - 42dB and this reduces the ringing effect they have at higher attenuations - Even clearer, quieter noise floor etc etc.
I continues to please and outperformed the outgoing MF bi amped solution I had by miles and another EL34 home design we pitted against it. Those in the know reckon it would take £3-5K to better.

There are loads of interesting designs http://www.lundahl.se/schematics.html
Plus their iron work is 2nd to none. The output Xformers in SoH are Lundahl.

If you want more info just ask.

 

Hey guys could you help me out a little??

Hey there guys,
Ive been getting more and more involved with valve amp's over the years and the first main solid state amp I bought was due to it's review's stating it almost had valve amp warmth and clarity.
I recently bought a small valve amp running two EL84s and its sweet as a nut.
I am running a set of Sonus Faber bookshelf speakers and a marantz CD63 KI signiature. I'm looking to upgrade my amp and have around £450/£550 to spend on a valve amp.
There are so many on the market with the influx of Eastern(Hong Kong/Chineese) amps to chose from and to be honest I have no idea what to go for.
Can you help me out as my solid state lasted me for over 10 years and I'd hope to be cool for another 10 with my valve choices. I know if i make good that I'll be blown away by the results.
I'd love to build one but am starting with an up and running set before I start thet journey!!!

Thanks in advance!

David

 

Hi David,

Welcome to the forum.

For your budget, I'd personally build a WD kit. Take a look at the following link:-

http://wduk.worldomain.net/acatalog/info_KEL84.html

 

Greetings, yes to be honest you can make your own very decent one for around £450 or even under.

However I recommend single-ended, not many Watts but loads of luvverly detail and 'cleanness'. Triodes are best, single 300B per channel or even a KT66 (a good one, genuine original NOS) wired as a triode is also a nice starter.

Even better is parafeed, which is where the 'transformer' isn't, it's actually just used as an anode load choke and the real transformer is fed from that via a blocking capacitor. Hence no DC in the actual transformer. Finally tried that with mine and was totally floored, wish I'd done it much sooner!

Below is what I'm using at the moment (o/p transformers under the shelf)

PM me if you're interested in an example list of bits

 

Hi i saw the dealer the Emporium with a Rothwell Rubicon amplifier,this would be a good start for you ,worth a look .
Valve amplification especially kits are a minefield ,
el84 and el95 valves will sound best , a bad single ended triode will sound horrible a good one is spectacular but you can not parrallel triodes so you are limited to under 10w and the best sounding amps are 5w , There is a valve called a 6528a which will give up to 20w and it is a triode check some of the usa diy sites
I can find out about an el95 amp that i know about and post back, these amps can also be run of a battery ,the first car audio in the big USA heavily sprung cars had record changer and amp using these valves ,Il think hard to see if there is a better option