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hnb2907 25th September 2007 01:49 PM

New toy
 
2 Attachment(s)
Hi folks,

I've just taken delivery of a new valve amp from China. Having spent a number of months looking around at what's available, toying with the idea of building a kit, I decided to buy something fairly simple that I can play around with.
I'm actually really pleased with it. For 250 including shipping, I think I've done quite well!

Main requirements were:
* a thick/heavy chassis
* decent looking fittings
* tidy layout/build
* single ended EL34's, didn't fancy replacing more expensive 300B's for example if I broke them
* valve rectifier
* big transformers
* not too expensive!
..and it doesn't fail on any of these.

The build quality is excellent, the components appear to be new, soldering/wiring/paintjob/general workmanship is excellent. The seller emails in good English, and has been first class to deal with in all respects of the sale. The amp arrived well packaged, got the tracking details so I could check its progress.

More importantly, since replacing the Electro Harmonix EL34's with some 10year old Svetlanas I had from a previous project, it sounds excellent.

Anyway, ebay item 270168183476 is actual photos of the one I bought - this being the first EL34 version of the 2A3 amp the seller normally lists.


The line up is 5Z3P (5U4), EL34 and 6J8P (6SJ7). The 6J8P are Shuguang as I also assume is the 5Z3P. The matched original EL34EH's were Electro Harmonix. All the valves were in new packaging.

I noticed that there was a slight mains buzz when touching the metal sleeve on the 6J8P. which I've now added a GND wire to pin 1, and the overall hum has reduced to a level that is barely audible in a quiet room.
My setup is an old Technics SL-PG370A CD player and Acoustic Energy Aegis One speakers (8ohm, 89dB, 120W). The amp seems to drive the speakers well at above normal listening volume.

I've got some NOS matched pairs of Visseaux 6SJ7MG and PHILIPS ECG 6SJ7WGT on the way to try as replacements for the Chinese 6J8P's.

So, I've backwards engineered the schematics, which I think I've got correct.

What I plan to do is to add a much bigger capacitance to 260V B+ (currently 2x 47u in parallel). Or, is it better to change the cap on pin 2 of the 5Z3P instead/aswell? Similarly, I'm thinking of a bigger cap on the 230V supply to the 6J8P's.

I also plan to upgrade the volume pot to an ALPS blue velvet, change to 100n inter-stage cap for something like a Hovland Musicap, and replace all of the shielded phono cable for something a bit more expensive looking!

Anyone got any thoughts on the schematics in general?

I'd also like to know if potential divider arrangement to the 6J8P heater connection can be improved. It's also possible that I'll move change the EL34 heater arrangement to include a hum pot close to the valve instead of a common GND on the back of the mains transformer. The PCB and chassis is designed for this, but not fitted.

When I can find my 8.2R resistors, I'll measure it's output power too....


All the best,
ChrisC.;)

hnb2907 25th September 2007 02:49 PM

Just noticed, I made an error on the schematic.

The 100n cap isn't connected to the 6J8P pin 4 / 50K pot wiper - it should be shown connected to the 8K2R / pin 6.


C
:smash:

chrish 25th September 2007 03:10 PM

Interesting. The "SV" series of amps are 'Sun Audio' and made in Japan either as a kit or pre assembled, they are point to point wired and use Tamura transformers. What you have looks like a rip off Chinese copy. The chassis and name plate look the same, even the transformers have a similar look, however I note that it is not point to point wired. Interesting is the shipping costs - very high. If you happen to be in Hong Kong, it only costs 160 pounds to pick up at the door!

Not having a go at you for purchasing this, I hope it works out well, just letting people know that it looks like they have taken advantage of someone else's design, ie it may be a pirate copy.

Here is a link to what the Sun Audio amp looks like http://www.eifl.co.jp/index/export/sun/sunsv2a3.jpg Notice the similarity...

Cheers,

Chris

hnb2907 25th September 2007 04:17 PM

Hi Chris,

Thanks for the reply...
You noticed the same as I did - it does look very similar to the Sun Audio SV-EL34, which is point-to-point wired. No offence taken. :)
That was one of the amps I was originally looking at... Having trawled around, there was some crud that I certainly wouldn't have given 250 for, irrespective of where it was made.

When I started to price up getting the bits in the UK to make one myself, and having to mess around making a chassis (I hate metalbashing), this looks like a reasonable alternative. I've got (what to me) is a good starting point for a bit of tweaking/learning.

I also doubt the transformers are Tamura. However, the mains transformer fills the case with only a couple of mm of clearance. The output transformers are also nearly as large.

From what I can gather of the Sun Audio EL34 offering, this isn't the same circuit as it uses 6N7GT instead of 6J8P's in the front end. But you're correct, it does appear that they've hijacked the aesthetics
:confused: Maybe Sun Audio buy their metalwork in from the same manufacturer or these folks just changed the design enough to prevent copyleft infringement?
Shame I'm not going to HK, otherwise I would have bought the Sun Audio amp, and hidden it in my luggage on the way home! ;)


Cheers,
ChrisC.

Jeb-D. 25th September 2007 06:51 PM

Not a bad looking piece you got there. It's appearance doesn't scream CHINA like most of them do. The output binding posts look better than most.

pred 9th November 2010 06:35 PM

I just stumbled on this topic, hope you are still all here.

I am interested in this amp, so do you have it still? Is it reliable? How is the heat on transformers (specially choke and PS tranie) after 3-4 hours of use?

Do you have some photos of the inside? How do you like it after 3 years?

Regards,
Pred

hnb2907 9th November 2010 07:13 PM

Quote:

Originally Posted by pred (Post 2359631)
I just stumbled on this topic, hope you are still all here.

I am interested in this amp, so do you have it still? Is it reliable? How is the heat on transformers (specially choke and PS tranie) after 3-4 hours of use?

Do you have some photos of the inside? How do you like it after 3 years?

Regards,
Pred


Yes, I'm still here, but not often!

The amplifier is in my bedroom (and can be seen in my avatar), and often played, as it is doing now, and left running for 12hours plus, usually at least once each week.

I found that originally the mains xformer and choke ran a little hot on 240V in the UK - just hot enough to hold in the hand. Most probably it is designed for 220V. So, I now run it through a 500VA 240V-to-220V auto-transformer. This has made it run a lot cooler to the touch. The heater and HT voltages were a little high when powered at 240V, but have now returned to normal on 220V.

It is currently driving an old pair of Roger LS7t speakers, which I believe are a fairly easy load. The frequency response measured on my 'scope into 8.2ohm resistors is fairly good and flat, and sounds fine across my hearing range.

I have replaced the interstage coupling caps, which helped. And also added an extra R-C stage on the main HT supply after the L-C.

Valve line-up is a pair of NOS Sylvania 6SJ7WGT (I think dated 1940-something), a NOS 1950's Russian 5U4 (can't remember what make but maybe Svetlana), and a pair of Svetlana EL34's which I bought new about 15 or 20 years ago.

I did toy with the idea of replacing the output transformers with some Hashimoto ones, but never had the time or spare cash to do it! Similar for replacing volume control pot with an alps.


If you privately message me your email address on here, I think I can find some pictures of the inside to send.

Had a quick look around ebay tonight, but now can't find anything which appears to be the exactly same, (mine is labelled "SV-2A3-EL34" as I had it specially made for EL34's based on their 2A3 chassis design). However, another seller now has something labelled "SV-EL34".

It probably isn't anything that would our audiophile friends would find exciting, but for me it's fairly decent valve technology, a well built chassis, it sounds good to me, and was within my budget - and looked a lot better manufactured than a lot of the Chinese stuff I'd looked at.


Cheers,
Chris

pred 10th November 2010 09:24 AM

I saw that they are a bit different now but still the price of 500$ is 4 times lower sun kits. I will rethink my budget and what to do.

My current amps are Quads II and they drive my JmLabs 91db very well and very loud if needed.

So I wanted to try something with lower power and was always intrigued by SETs. Since in my surrounding nobody is into HiFi at all I can not hear them in my system in a different way, only if I buy something.

In next months I will sell a lot of stuff (my Assemblage ST-40, JLH 15W that I made, one thoresns TD320 etc...) and hope to raise some cashe to buy a SET. One of my other choices is the Elekit TU-879S. Although the components in this one from Tube Depot should be better I like more the looks of SV-EL34. And also looks it is more easy for modding...

Regards,
Pred

PS
I have sent you the PM

ray_moth 12th November 2010 10:03 PM

I noticed a question in the original post which seems not to have been addressed, concerning the filter cap size. DO NOT increase the first filter cap any further -- at 47uF, it's already in excess of the maximum 40uF specified for 5U4!


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