Hi-end 845 with only two stage

[audiodesign]

Kevin,
Yes, with the 211 the voltage gain and swing since to be ok

Using the 845:

Ri=1700 u=5.3

with 11K5 (LL1620 con.B) we have Rout=1700/(38*38)=1.2ohm good to drive any loudspeakers

to get 10Vrms on 8ohm (Pout=10*10/8=13w) you need Vg=10*38/5.3=72v

Using the 211:

Ri=3800 u=12

with 11K5 (LL1620 con.B) we have Rout=3800/(38*38)=2.6 too high to drive normal loudspeakers

with 23K(LL9202 con.B) we have Rout=3800/(53*53)=1.35ohm

to get 10Vrms on 8ohm (Pout=10*10/8=13w) you need Vg=10*53/12=44v

but the 211 at 530Vrms on anode will be linear like the 845 at 380Vrms ?

Probably it is true using the 211 and 23K transf. at higher plate voltage near 1200v

With a 23K the bias current necessary is low so only 60mA will be enougth

So is true that the 211 give less problem as input swing but it need higher power supply voltage to get same power and this mean more difficult to find good components with 1500Vdc like the capacitors.

For a more precisious calculation add internal resistance of transformers (prim. and sec.).

[revintage]

Hi,
Maybe this is a little far out, but why not make a Lundahl transformer coping with more current by adding an opposite current through the secondary? This to get rid of the capacitor and still get enough inductance. If 4:3,5 doesn´t give enough gain, one could go 3,5:4.

[audiodesign]

Using the 6HV5A is very difficult use interstage transformers because these need an inductance value about 100H and 25-30ma of dc current

[kevinkr]

Originally posted by audiodesign
Kevin,
Yes, with the 211 the voltage gain and swing since to be ok

Using the 845:

Ri=1700 u=5.3

with 11K5 (LL1620 con.B) we have Rout=1700/(38*38)=1.2ohm good to drive any loudspeakers

to get 10Vrms on 8ohm (Pout=10*10/8=13w) you need Vg=10*38/5.3=72v

Using the 211:

Ri=3800 u=12

with 11K5 (LL1620 con.B) we have Rout=3800/(38*38)=2.6 too high to drive normal loudspeakers

with 23K(LL9202 con.B) we have Rout=3800/(53*53)=1.35ohm

to get 10Vrms on 8ohm (Pout=10*10/8=13w) you need Vg=10*53/12=44v

but the 211 at 530Vrms on anode will be linear like the 845 at 380Vrms ?

Probably it is true using the 211 and 23K transf. at higher plate voltage near 1200v

With a 23K the bias current necessary is low so only 60mA will be enougth

So is true that the 211 give less problem as input swing but it need higher power supply voltage to get same power and this mean more difficult to find good components with 1500Vdc like the capacitors.

For a more precisious calculation add internal resistance of transformers (prim. and sec.).

Good analysis, and I actually need the higher source impedance because of the way my speakers were designed.. Will probably run something like 12K opts. I plan to run at something like 1.1 - 1.2KV in all likelihood and have access to the high voltage components required.

[audiodesign]

Paolo,
the 6HV5A have low microphonic effect

if I tapping the bulb, I can hear a little tic on speaker but very low

[rdf]

I found the 6HV5A eats voltage and really starts singing over 1kV.

[waltube]

Hi Andrea,

as I mentioned you, the best result I got is with 6H30, parallel ( are easy to select for similar sections), with a Tango NC20 interstage at 20 mA of Ia; the swing is 185 Vrms/530 Vpp ( at less than 2% of distortion.
The Va is about 250 Vdc. I am close to the limit but the tube is really strong.

Another tests

http://www.multitask.it/845/1403-1Kh...15vin-nc20.jpg
at this addres there is a FFt with 6BX7 and NC20 (another test) with 20mA at 1KHz, 3% THD; Vout about 130 vrms. at 20 hz the result is good.

http://www.multitask.it/845/1403-1Khz-50mA-nc20.jpg
at this link there is a FFT with the same setting but with 50mA of Ia; the 3% of THD is at 150 Vrm at 1KHz, but at 20 hz it is very bad.

http://www.multitask.it/845/1403-1Kh...-5vin-nc20.jpg
athis link is the same circuit with 20mA of Ia , 5 Vin, 40 Vout, 1 KHz; the IIIrd is low.

Bye

Walter

[inertial]

Oh very thanks Andrea, a precious information !

Cheers,
Paolo

[audiodesign]

Walter,
6H30 or many other tubes have no enougth voltage gain to create a real two stages amp.

You probably use the amp with a pre-ampl so this mean 3 stages.

[waltube]

Andrea,

if you use the Sowter 8540, 1:4; loaded with 50k you have 3K of input impedance; this will help.
This means that with a G of 8 with 6H30 ( I have to check on my notes), with a Vin 2 volt (normally output for a preamp) we have 8 volt on input of 6H30 and 64 volt at the ouput of this stage.

Bye

Walter