Hi-end 845 with only two stage - diyAudio
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Old 4th November 2008, 09:05 PM   #1
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Default Hi-end 845 with only two stage

yesterday evening I have started some measurement about 6HV5A used like 845 driver.

The schematic was very simple: inductance on anode, Rk = 100ohm, Ck = 470uF, Rg = 75Kohm and output capacitor 2.2uF on 33 or 100Kohm load.

With medium voltage operation (about 600V) these tubes give low sperformances because distortion is high 1.1% at 25Vrms.

The good result are obtain using 980V and 100ohm on catode to keep the power nead the 30w (35w is the maximun allowed), bias about 30mA.

With these value I have got the good 1% at 120Vrms on 33Kohm load.

The freq. response is limited to 50Hz(-3db) with 20H but it will be 10Hz(-3db) using 100H 50mA Sowter 8982.

The voltage amplification is 120/0.7=155x.

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Old 4th November 2008, 09:06 PM   #2
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Finally the first test result using 6HV5A to drive 845

6HV5A loaded by 20H (Rdc=70ohm) and Rk=100ohm Ck=220uF
950V 28mA

845 loades by Tango X-10S 10K/8ohm Vg=150v Rg=22Kohm
950V 100mA

10Vrms on 8ohm with 2% thd

Interstage 2.2uF // 0.33uF Audyn-Cap Plus

Very good sound

Very good voltage gain

Power can be increased using 1100V instead of 950v

Soon next test and photos
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Old 4th November 2008, 09:07 PM   #3
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Clio measurement

10Vrms on 8ohm
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Old 4th November 2008, 09:38 PM   #4
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The 20H inductance is only for this first test.

I am thinking to change this with LL1668/25mA

See actual frequency response
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Old 4th November 2008, 09:40 PM   #5
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the LL1668/25mA
have 100H so about 5Hz (3-db)


Andrea Ciuffoli
www.audiodesignguide.com
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Old 4th November 2008, 10:01 PM   #6
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test environment

Soon measurement with Lundahl AM output trasf. series
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Old 5th November 2008, 02:41 AM   #7
N1ESE is offline N1ESE  United States
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Good work so far, watching the development of this.
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Old 5th November 2008, 08:24 AM   #8
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This is the first schematic
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Old 5th November 2008, 08:35 AM   #9
Gluca is offline Gluca  Italy
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Andrea

did you try, or will you try, a grid choke for the 845? Things get usually better with them

Ciao
Gianluca
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Old 5th November 2008, 08:39 AM   #10
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Hi Andrea,

I am right now in the process of building your 'New 845' with the EL34/845 combo.

This one looks a lot simpler. How does it compare? Can it be driven direct from a CD player

I am just about to finalise the power transformer order. Should I hold off? I would love to see a schematic of your power supply.

Cheers,

Rob
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