eBay Chinese Valve amps?

[kt66se]

Hi,
Just joined this forum to try to learn more about valve amps as I would like to build one. I noticed that the HiFi World did make a lot of amps but looking now they only have a few, I am guessing things are in the air a bit?
I also looked on eBay and noticed chinese 300B amps for silly money, the amps look great, transformers look big, specs look good - whats the catch? If I were to make one, say a KT88, it would cost more than twice the price of a 300B SE in polished ali with wood sides! I watched a 300B sale last night on eBay, the bidder won it for £150 and had £95 to pay for delivery. That's £245 for a 300B SE, with valve rectification, hard wired and beautiful finish.

Oh, what to do, what to do!
Does anyone have any experience with these amps, there must be some kind of catch, maybe export duties to pay, cheap components, dangeous wiring - something?

Anyhow, dispite the eBay stuff, I would like to build something around the KT66 valve, I looked at the Aurora and that seems quite simple to build, do you think HiFi world will start producing more designs, would it be worth waiting to see what comes out? I think I like the idea of single ended over push and pull. I have looked at transformers at Sowter and they have stuff to match 2 KT66 in pairs.

Any advice greatly appreciated,

Thanks in advance

[Richard]

Hello and welcome

Things were up in the air at the beginning of the year (when WAD closed and WD was born) but are now very much on the ground. The range now stands at 2 amps with more on the way. The important part though is that supply and quality has been improved and everyone who's ordered kits since Peter set up WD has reported good service.

With regard to your choice, why choose the valve then the circuit? I'd recommend a listen to as many valve amps as possible and decide from there. An open mind about valve types and circuit topology may surprise you and even if you have a stash of KT66s they will only be a small part of the cost of a new amp so start afresh.

Other parts of your system may influence a choice. Which speakers, source and room size do you have or is it all a blank canvas?

Rich

[pre65]

Hi KT66se-if you enable your location in User CP you might even get offers to listen to some "other" valve amps !

Richard is right,the valve used is only a part of the mix.

initially your existing system,esp loudspeaker sensitivity,will dictate the watts you need and therefore to some extent the valve and amp type.

from my (limited) experience the more sensitive the speakers the more choice you have of some very nice low powered valves.

i myself have graduated to full range Fostex 206 and am embarking on building a 2W Gordon Rankin 45 amp,which should enable me to capture the single ended magic,that my 300b se hasn't quite got.

Philip

[kt66se]

Hi,
Thanks for that, I live just over the border between Shropshire / Mid Wales and would love the chance to have a listen to a few amps. I use Yamaha NS200 speakers, floorstanders at about 90db sensitivity. I don't like them, have not seen anything in the shops I like, Wilmslow seem to offer a better range but are blinking expensive, so no doubt I will take the self build route with the speakers as well. Room is big, bigger than Yamaha's seem to be able to handle, not much bass etc - but you wouldn't expect it with 6inch cones

I like the idea of single ended, don't know why? Maybe they can be run more class A for a sweeter sound? My Dad did own a Williamson pair of mono blocks driving HPM120 speakers and I loved the sound of that - (I know, push pull but used KT66), alas, they were dumped when it was deemed the right thing to do, like rip out Victorian fireplaces, carpet over, or even worse rip out floor tiles and artex ceilings!

Things about me -
I don't have things to loud, it annoys the kids! So not looking for anything above 20watts? I don't have any valves, will need to buy so choice is open as to what to use - although I do have 6 Mullard EL34's in a Soundcity guitar amp that works but is not used.
I do have electronics experience but am not familiar with things like working out NFB, gain or anything to do with maths! I built a Gainclone, it's ok but looks boring, my favorite valve is the KT66, my favorite transistor was the 2N3055 as used in the NAD3020 but Creek beat that with the TIP35 etc.
I like Jethro Tull, Cream, Lilly Allen, Bare Naked Ladies, (The Canadian Band)
and other strange stuff that my kids think are really un-cool.

My metal work skills are non-existent, this is the only thing that will steer me towards buying a kit over making one from scratch!

Cheers

Adam (Kt66se)

[pre65]

Hi-how are your woodwork skills ?

i use the Fostex 206 in cabinets made from a kit that Wilmslow audio supply (mine came ready built) and have a very good sound,even more so with the phase plugs fitted.

see this link for the Fostex cabinet details and Wilmslow for the cabinet kits (£213 + vat)

http://www.fostexinternational.com/d...6e_enclrev.pdf

https://secure.wilmslow-audio.co.uk/..._Cabinets.html


Philip

[Ianm2]

the chinese amp construction can vary from excellent to shoddy.

I am not talking about superficial appearances, but actual implementation and quality.

you may also get caught with duty which puts the price up, and royal mail take a big cut, too.

it may take months to arrive with surface shipping.

the transformers may look big, but they are the weak link, the mains tx is also specced for 220 volts, run hot, and radiate magnetic fields badly.((this can cause electrical and mechanical hum problems, the output tx's, too are not good at all, its the winding, despite being quite large.))


knowing the chinese, I would not trust the insulation in the transformers, too. They seem to know how to implement the circuitry, but are not known for thier adherence to safety regulations.


Finally, I had an amp from china which didn't even have a safety earth, with 500 volts inside, if the case became live its goodbye time.

you can drop kt66 kt88, el34, 5881, 6l6, which are all interchangable, without too much mods, 1 resistor, perhaps not even that.

class A does not give a sweeter sound in itself.

Class B amps usually give lower distortion, but they need higher feedback to achieve this, this is what gives the sound difference imo.

300b amplifiers only give 7-8 watts, 5% plus 2nd harmonic, they are usable without feedback, as the harmonic is lo order, and not considered offensive, due to that they have astounding midrange palatabilty and tangability, but it takes some skill and experience to do one that does bass, and 99% of them have limited drive.

the only ways, as someone here has done, is an aikido circuit, which I wasn't enamoured with, in my pre implementation of, but he has reported excellent results,

parallel feed may help, otherwise, extremely skilled design with

1/ top power supply,
2/ driver stage is vital to 300b, and
3/ very good output transformers, BIG!! most around 2kg, which still give that lovely midrange, and are listenable in absoulte terms, but not optimal.

5kg at least I would say.

( so I suppose, as with all amps, its not just one thing in isolation, but a combination of output stage, power supply design, and circuitry that goes before it, it just becomes blindingly obvious in a single ended without feedback how critical all these components of an amp are, as 300b is notoriously dependant on all.)



There may also be an inherent limitation current wise in 300b tube that means it cannot chuck anything worthwhile out, but I haven't ever looked into that.

Otherwise, forget 300b.

[kt66se]

Hi,
Thanks for that, I will keep away from eBay temptations. I have just looked at the gallery pictures on this site and I reckon with a bit of steel, some wood, glue and a few nails I could knock something up

Your amps look good and have inspired me to pursue the home build way.
The Fostex cabs look very complex for a single cone? Don't know anything about this drive unit, I've heard of transmission line - TDL did them?
I like the idea that the cab could produce a good low end sound. This always puzzled me, why design your amps to give a wide bandwidth when most speaker cabs will never come close to producing anything lower than say 35Hz! But then again, why not. The guy who designed the EAR valve amps design theory is that the sound should sound the same on speaker out as line in - but does this fail on valve amps that add their own tone?

Anyhow, don't care, in the end it would be nice to have an amp that has a wide bandwidth and a set of speakers that will grace it for little money

300B's look to complex, so will go for either the KT range or EL's. Maybe the 5881? Not sure....but thanks to all

going to look up aikido circuit's now????

[pre65]

Hi-why not go to "The Shadow" web page and view the kit he has built for himself.

http://web.mac.com/scress1958/iWeb/S...ials/Home.html

Steve has built some most excellent gear and you may find something like "rocky" an ideal amp to start with.

all in all a very good site to visit.


Philip

[prince of darkness]

Hi'
I agree with Philip, Steve has shown what can be achieved by someone with little initial knowledge, who is prepared to put the time and effort in. Members of this forum who have heard his projects (not me ) have been impressed and his website is excellent also.
Alternatively you could check out Triode Dicks site, which has a lot of designs, SE and Push Pull, Beam Tetrode and Triode. Text is in Dutch (try using Babel Fish to translate, for a laugh), but the schematics are clear and easy to follow. Transformer sets are available for several projects from AE. The 807SE looks to be a very affordable route into single ended amplification and should probably be ok using 6L6/KT66 or EL34 type valves.

http://www.triodedick.com/
http://www.ae-europe.nl/uitgangstrafo_engels.htm

[kt66se]

Pre65 / Prince of Darkness,
Thanks, have just got back from the shadow web-site. Very impressive, I also like the way he appreciates all the help he has had from the WAD forum He seems to favor LCR caps? They look massive, is this the way to go. Where do you source your components from? I use Radio Spares
(Maplins seems to have left the electronics world behind in favour of kits and 350Gb hard disks)! What about metal work, can you get chassis from somewhere?

Now off to try triodedick!
Must remember to do some work as well!