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PostPosted: 13 Apr 2010, 22:18 
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Joined: 15 Dec 2009, 20:16
Posts: 86
Well, .........the mono breadboarded version of the attached schematic is done!

Have made the following changes due to sensibility, budget and practicality:
1.dispensed with input transformer and replaced with 100k stepped attenuator, and paralelled 6sl7 input stage, cap coupled to first 845.
2.dispensed with inter stage transformer due to difficulty in robbing a bank to obtain a good enough unit :mrgreen: .........went with cap coupling direct to last power 845 valve.
3. running filaments on AC at the moment, but looks like I may eventually neeed to go DC?
4. only using one power supply choke............will look at more further down the track?
5. this time, and for the first time in building valve amps, I have used SOLID STATE (high quality, expensive IXYS rectifier bridge) rectification. My impressions on this?................don't believe the B.S about valve rectifiers being better than S.S.!

SOUND ????.............INCREDIBLE!.........only 4 watts, but sounds like 40!
Very dynamic, effortless and revealing of micro details. 845's are just the standard regular Chinese Shuguang.

Waddya reckon??? :smoking:


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PostPosted: 15 Apr 2010, 01:54 
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Joined: 15 Dec 2009, 20:16
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So,.....................................no one gives a hoot!!!????? :eek:

This forum looks very lame to me :lildevil:


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PostPosted: 15 Apr 2010, 02:37 
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Joined: 02 Mar 2009, 12:41
Posts: 1110
Location: Vänersborg, Sweden
Put it this way ... people tend to get scared with voltages above 500V and temperatures above 800 degrees C....

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“If you don't know where you are going, any road will get you there.”
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PostPosted: 15 Apr 2010, 22:20 
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Joined: 15 Dec 2009, 20:16
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That's a shame as 500v is almost half the normal operating voltage of the 845.
;) ;)
At this voltage(500v) there is no further danger than 350v, and there is no possibility of voltages arcing across to the chassis etc, as there is in the 1000v+ range.


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PostPosted: 16 Apr 2010, 01:50 
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Joined: 24 Feb 2009, 03:24
Posts: 562
Location: USA
See, please, this forum.....
http://www.basaudio.net/gm70/index.php?action=forum

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Hi End is back proportional to the number of composite parts!
Projects: OTL 6AS7 Gen, Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, PP 6005 Gen. Ellectric , headphone ampl. OTL Loftin White 6AS7 RCA....SE E84L& E80CC Siemens&Tel-n.
http://azazello-sound.blogspot.com/


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PostPosted: 16 Apr 2010, 02:15 
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Location: Vänersborg, Sweden
Ziggy: Ich war seulement joking ...

Still I haven't run any amp at higher voltage that 360V, but I will try to reach 500V soon.

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PostPosted: 16 Apr 2010, 21:28 
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Location: Winnipeg, CANADA
Wow - sounds like it is really expensive and very heavy.

For one channel: 1 power transformer, 5 chokes, 2 audio interstage transformers and 1 audio output transformer. :shock:

Please post a photo of your proto. I'd love to see it.

What did you use for the interstage transformers?

Did you consider a regulator lime the LM338 for the heaters?
Cheers

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PostPosted: 17 Apr 2010, 12:37 
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Joined: 21 Dec 2009, 15:51
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I use 6sn7 for driver and input for my 845s lots of grunt.
Also the plates are 880 Volt 84ma.

Nearly 20 Watts.
This is a modded music angel not a scratch build.

FTI


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PostPosted: 22 Apr 2010, 21:11 
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Joined: 15 Dec 2009, 20:16
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I don't know what it is about this 845/845 ''beast'' (and I'm using MUCH LESS transformers)but it has a sound that is extremely addictive and compelling to listen to.

Music sounds so ''right'' that it's eery :hot:..............it can stop you dead in your tracks and force you to take note of the musical performance ,not just the sound quality ;)

I have a ZCA single ended mosfet amplifier running also at the moment and it is a brilliant amplifier for solid state.I mentioned on another thread, that the 845/845 amp seemed to sound noticeably inferior to the ZCA, but, after changing the signal caps to Audionote copper foil in oil variety, transparency and all other areas of sound quality have sky rocketed!
Just goes to show what a few small component changes can do :eek:

I have discovered that the ZCA doesn't draw you in to the performance or sound as ''organically alive'' as the 845/845 which simply sounds like live music 8-) .........especially in ''presence '' and ''accuracy in musical instrument tonality'' :wine: .

There has been a lot of discussion and amps built around the world using this low voltage topology and they all seem to rave about the sonic qualities.........................have to agree..................a 300b amp, run at various operating voltages and configurations has never sounded this good to my recollection. I know because I have built many variations and have been a 300b fan for a long time.............until now :twisted: :D


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