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Old 5th November 2008, 08:45 AM   #11
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The voltage gain is like my 845 amp.

http://www.audiodesignguide.com/New845/New845v2.html
http://www.audiodesignguide.com/New845/New845v3.html

so it can be driver directly by a phono-pre or any CD player

and it does not need a low impedance source like the amplifier with input transformers so it can be driven with normal sources.
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Old 5th November 2008, 08:49 AM   #12
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Thanks Andrea,

So how does it sound compared to your "New 845" and if you could build only 1, which would you choose?

I also noted that you initially had problem with noise due to gain and then added the DC rectification - do you have the same issues with this one?

Rob
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Old 5th November 2008, 10:12 AM   #13
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This amplifier is in develop phase so some changes will be necessary to ear the final result.

In a first comparation test yesterady evening I like very much the sound of this new amp.

The my 845 amp. use Jensen copper film paper in oil interstage and this new two stage 845 use a MKP cap so a real comparation is not possible.

The my 845 amp. use Valve Art 845 and this new two stage use 845 Shuguang.

So a real comparation at this time is not possible but I will do this in the next weeks.
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Old 5th November 2008, 11:36 AM   #14
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About grid choke for the 845: never tested, to study
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Old 5th November 2008, 04:54 PM   #15
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Hi ,

Just for curiousity, is it this 6HV5A microphonic ? What happens if you
tapping the bulb, can you hear something from the speaker ?

Cheers,
Paolo
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Old 5th November 2008, 05:05 PM   #16
kevinkr is offline kevinkr  United States
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Interesting design Andrea, I'm working a two stage 211 based amplifier using the 5842/417A. Like yours also fixed bias and a 100H magnequest choke (exo-001) to load the 5842.. I have a pair of GE VT4C that will go in this amplifier.

Have not yet decided on the OPT..

Supplies per my usual practice will probably be regulated - might reconsider that if I end up using a parafeed configuration on the output stage.
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Old 5th November 2008, 05:08 PM   #17
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In not normal use a 5842 to drive the 845 because the 5842 have too low voltage swing and too less voltage gain
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Old 5th November 2008, 05:15 PM   #18
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to increase the voltage gain you can use an interstage transf. 1:2 like the LL1660/10mA with primaries in parallel

In this case the D3A is teh best choice (see my measurements on http://www.audiodesignguide.com/PF2007/PF2007a.html)

The main problem using a 1:2 interstage transf. is the low output current.

I like very much the Lundahl with amorphous core as OPT.
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Old 5th November 2008, 05:28 PM   #19
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by audiodesign
In not normal use a 5842 to drive the 845 because the 5842 have too low voltage swing and too less voltage gain

Quite well aware of that, but I have 211/VT4C tubes in hand which have much higher mu (11) than the 845.. I was just commenting on the similarities, not suggesting you (or anyone to be clear) even consider the 5842 for this application.

I think even the D3A would be pretty marginal driving the 845, at least in triode connection even with a 1:2 step up IT.

I'll definitely check out what I can get the Lundahl amorphous core opt for in this country - it might be an excellent choice for my amplifier.
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Old 5th November 2008, 05:58 PM   #20
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Default D3a - Gm70 option 2stage option

Andrea, you have the irons, you have most of the circuit needs, why don't you try the promising D3a - Gm70 2stage SE solution, D3a can do the trick also with 1:1 interstage...
Regards,
George
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