805 SE amplifier

[Julien]

Exactly what words did I say that you think are disgraceful and should be supported by evidence presumably to make them not disgraceful?

Sheldon,
Thanx for the support. I think Julien has financial interests in the sale of his favorite Chinese 805A and is therefore sensitive to any comments that look like they may be critical of it.

Those who posted the words should be responsible for them and give the evidence.
You are a villain with ulterior motives. I've never thought that any topic without a theory discussion would be occurred here.What I've said was tested by myself and know the parameter of any 805 by test or by datasheet.
I noticed that you know Chinese,and I'll send you a word in Chinese:ÒÔСÈËÖ®ÐĶȾý×ÓÖ®¸¹

 

[Julien]

Just to be clear. I am not blaming you in any way for what I believe to be an error in calling the tube you like an 805A. How could I, it wasn`t your doing. Furthermore, I`ve never said that it (your tube) was not a great sounding audio tube (I have not heard one so cannot form any opinion). The only thing I have done is point out how it is not an 805.

I've told u several times that China improved the 805 tube in 1970's.Not to mention the physical structure of it.the only thing we are interested in are the electric parameter of 805(Chinese 805 has a better one).Anyone of us shouldn't say it isn't a 805 tube.It's affair of Shuguang electrion factory.
About the 805A,Shuguang factory said it was manufactured for audio amplifier and safer for audio fancier in China in 2001

 

[Julien]

Low impedance does not eliminate the introduction of phase shift which you also mention can become a problem with amplifiers employing large amounts of global NFB to reduce output Z and improve loudspeaker DF. The answer is less global FB and careful use of local NFB in the output stage itself (if really needed). One can also choose to employ speakers that are inherently better self damped with SET amps and thus stay away from high levels of NFB entirely. Horn loudspeakers are probably the best example of highly self damped speakers and also highly efficient. No wonder they seem to find popular pairing with low power SET amps. A good synergistic relationship!

A low impendance,of course,does not eliminate the introduction of phase shift,but an IT will.
If you want to use the local NFB in the output stage,it will increase the driven voltage of drive stage.Thus a power output tube should be used here which can be made another amplifier.
The less NFB wouldn't reduce output impendance to a efficient level,even more the THD.
The lowest input Z of a RCA 805 tube is less than 500 ohms,the largest one is over 10K ohms.You could imagine the change of Z at the IT stage,and it will course large distortioin.I've test an IT stage.When a step signal was inputted,a small oscillation occurred.How it could deal with a sudden signal in music?
If I've got a high efficient loudspeaker,I'll use a 300B SE with lower power insead of a 805 SE.And that's enough.
If u still immersed in the guess that I've financial interest in it,there is no need for me to post any reply.You could dislike a tube by it's sounding or looks in your amp.But u can not judge a tube by it,for what you've heard do not represent ours.

 

[thomash85715]

my own ming da story

Hi: I just bought a used ming da 3008 from a guy in tennessee. It is working OK so far but my plates are a tiny bit red; only visible when I shut it off. The filament glow is so overpowering as to otherwise obscure it. I have tried in vain to get bias pot setting info from nysound who is distributor. Can any of you help? I have a current meter; just not sure where to connect it and what to adjust for. Also, whichever tube I put in the right side glows a bit brighter on filament. Does that indicate a bias misadjust or more serious flaw underneath? And where is the main power fuse? I can't find one anywhere on this thing! It has a delay relay which functions OK (after I changed it out.) All help appreciated; since I am still under surveillance, I cannot email any of you directly so please respond on the forum. Thank you. --Tom

 

[kor952]

Hi,

I just placed a picture of my Shishido 805 amp in the photo gallery....and a URL where you can read about it (German) and find schematics etc.

newbie,

Ronald.

 

[rcavictim]

Hi,

I just placed a picture of my Shishido 805 amp in the photo gallery....and a URL where you can read about it (German) and find schematics etc.

newbie,

Ronald.

How about a hotlink here to your other post with pictures, etc.?

 

[kor952]

I'll give it a try, here's the link to the Photogallery

my Shishido 805 (link to Photo Gallery)

 

[rcavictim]

Very nice work Ronald. That 300B amp is sweet also.

I note cathode FB on the 805 from the output iron. Whose xfmers did you use and what plate Z? Nice you were able to find a suitable interstage xfmer as well. That makes Class A2 somewhat simpler to implement.

 

[kor952]

Very nice work Ronald. That 300B amp is sweet also.

I note cathode FB on the 805 from the output iron. Whose xfmers did you use and what plate Z? Nice you were able to find a suitable interstage xfmer as well. That makes Class A2 somewhat simpler to implement.

All transformers are from Tango (see the special wound nrs in the diagram) only the power transformer was wound by a Dutch transformer factory. The interstage transformer is a so called Inverting Interstage Transformer (IIT) the positive tension on the grid of the 805 causes a current through the sec. of the IIT that cancels a part of the anode current of the 6L6 (wich flows through the primairy of the IIT).
The problem is that these special wound transformers at this moment are hard to get from ISO/Tango.
Because of the cathode feedback of the OPT the impedance of this transformer may be lower as useally, in this case the Rp of the OPT is 3.5 K. Also the Anode voltage of the 805 is "low" 820V but the Anode current is high 135 mA.

Ciao,

Ronald.

 

[LineArrayNut]

thomash85715

Don't worry about the red hot plates. Carbon anodes are supposed to be hot for "getter" action. My own BEZ T10B-1s' 805s are red hot and hammer great tunes with no problems. They are the earlier schematic posted and sound great. Still working on the Ballantyne MX-24's 200 watt push-pull 805 monsters, but they glow red also.
my own ming da story Post #64
(Hi: I just bought a used ming da 3008 from a guy in tennessee. It is working OK so far but my plates are a tiny bit red; only visible when I shut it off. The filament glow is so overpowering as to otherwise obscure it. I have tried in vain to get bias pot setting info from nysound who is distributor. Can any of you help? I have a current meter; just not sure where to connect it and what to adjust for. Also, whichever tube I put in the right side glows a bit brighter on filament. Does that indicate a bias misadjust or more serious flaw underneath? And where is the main power fuse? I can't find one anywhere on this thing! It has a delay relay which functions OK (after I changed it out.) All help appreciated; since I am still under surveillance, I cannot email any of you directly so please respond on the forum. Thank you. --Tom)

 

[LineArrayNut]

TugaTweaker BEZT10B-1

I have those amps and they are nice. They have bass, smooth mids and nice highs. It sure looks like to me that the 6SJ7 is trioded too.

(805 SE amplifier Post #58
I would like to use them in this but the pentodes 6J8P , 6SJ7 , 6H8 , etc
never heard of them . Why not the usual 12AX7 , or 6SN7 ?)

Extra drive needed for the A2 driver stage necessitates higher gain for the input stage.

 

[tubalu]

Julien ' 805 design £¬please click here http://bbs.hifidiy.net/viewthread.php?tid=67950&extra=page=1

 

[rdf]

 

[LineArrayNut]

Pp805

These posts got me interested in what the 805 can do. According to the RCA datasheet a PP pair will make 'approx' 370 watts at under 3% THD. If I read it correctly this is driven by a pair of IT-coupled 2A3. Very impressive!

It's more like 200 watts clean, well over 300 before clipping.

6SN7 differential IT 6B4GPP IT 805PP finals. 20-20K full power -3dB

An externally hosted image should be here but it was not working when we last tested it.

 

[Klimon]

beautiful

 

[TugaTweaker]

http://www.4shared.com/file/77943365/7ad40054/805SE.html

Its a Nobu Shishido 805SE design! I got the interstage from EIFL
Japan. I am really happy with the fenomenal soundstage . I decided to use the russian 6C45 , a we437a direct sub ,it does a good job . Yes i know about oscilation problem . I don't ear anything odd ,only a little hum that i will take care when i have a usb pc oscilloscope .
I must thank all the Masters of our Diyaudio for the support and free knowledge spread that made possible, me a less educated in electronics person to achieve this . God bless you all !!!

TT

 

[LineArrayNut]

Nice!

as mentioned earlier in thread...