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.

audiodesign has attached this image:
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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

Clio measurement

10Vrms on 8ohm

The 20H inductance is only for this first test.

I am thinking to change this with LL1668/25mA

See actual frequency response

the LL1668/25mA
have 100H so about 5Hz (3-db)


Andrea Ciuffoli
www.audiodesignguide.com

test environment

Soon measurement with Lundahl AM output trasf. series

Good work so far, watching the development of this.

This is the first schematic

Andrea

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

Ciao
Gianluca

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