6V6 line preamp

[stajo]

Interesting also that he visualises the electron wandering path and not the usual current show that is more common nowadays. Like in my past physics classes that I probably slept through.

 

[Salas]

It suggests 1970 in the description but judging from the age of that oscilloscope it must be late 50's to early sixties film vintage

 

[Salas]

Gotta love the way it has "LOAD" slapped on the scope in B movie poster like font on 11:40

 

[stajo]

A physisians robe is what we need. Handed you an email of some stuff i had forgotten Nicholas.

 

[gtoro]

Two keys to a good tube based CF tho. High transconductance tubes and a stiff under lip. Try sim a CCS in the bottom instead of a resistor that steals your voltages. Or a proper inductor. Will save you voltages and give you the oomf. An active CSS is about the same as a large inductor and as a very large cathode resistor. Just that your resistor has to be in the Mohm class to compare and THAT would steal some voltages.

You're right, I'll try it on actual gain version on anode instead of the resistor and in CF version too.
I'm still waiting for Lr8 but I've two dn2540 in my hand...

 

[gtoro]

May be in these days i'll go to solder a ccs based on dn2540 to try it instead of anode resistor, this implies the choice of fixed current to flow in the tube. I'm thinking about 18-20 mA any suggestion?

 

[Salas]

That's about the typical anode current used in this preamp and its a good bias point. DN2540 is not working that well below 20mA anyway. Not changing the typical current level will make your comparisons more controlled also.

 

[gtoro]

Dear friends last evening tried ccs based on dn2540 and lm317 as expected i save more voltage on anode but i tried various fixed current bias among 16 and 23 mA, the sound to my ear was not so exciting like ehat i listen whit simple resistor so i rool back.
Did you experienced the same or i done something wrong?

 

[Salas]

If you will look way back on when I used anode CCS with enhancement mode MOS cascode I rolled back also

 

[gtoro]

I built a LR8 based regulator too and finally i have 297 volts before anode resistors the sound was definetively good, now i have to try space inside.....
Next step your hvssv2 but for the moment i will enjoy the music.....

 

[gtoro]

A short update, I put the CCS I've built for anode load after regulator and before anode resistors configuring it for 40 mA (actually I mesured a 14 mA on cathode) to give current to both andoes, It run quiet and fresh and I gain, at my ear, more "black" on musicless parts loosing about 6 volts.
I leave it and in next days I go to lessen better, do you have contraindications or suggestions about?
thanks for any answer

 

[buzzforb]

Salas, how does one determine the screen resistor value? I was looking at a 6v6 version of the musical machine and he used 330 ohms plus a Schottky diode. His explanation was that the diode was intended to make the resistor "disappear". Thanks ahead of time.

 

[TonyTecson]

the resistor is there to make it a triode, and to discourage the tube from self oscillation, value is not critical imho, the diode does not really serve any purpose in there...

 

[buzzforb]

I understand the purpose of the resistor, the question was more about the importance of the value and any gain in using a diode. Thank you for the answer.

 

[TonyTecson]

for me any value between 100 ohms and 1k will work just fine...

 

[buzzforb]

thank you

 

[Salas]

Salas, how does one determine the screen resistor value? I was looking at a 6v6 version of the musical machine and he used 330 ohms plus a Schottky diode. His explanation was that the diode was intended to make the resistor "disappear". Thanks ahead of time.

I generally use the lowest value I can avoid oscillation with

 

[Vbenonisen]

Is the triode connected 6V6-tube hard to drive (Miller), or can this preamp be used with any wimpy source, lets say a Mp3-player?

 

[Salas]

Its not hard to drive its capacitance (~35pF socketed for the gain version), especially if the source's impedance is no higher than 1K and the volume pot is low value, say 20K

 

[Salas]

A short update, I put the CCS I've built for anode load after regulator and before anode resistors configuring it for 40 mA (actually I mesured a 14 mA on cathode) to give current to both andoes, It run quiet and fresh and I gain, at my ear, more "black" on musicless parts loosing about 6 volts.
I leave it and in next days I go to lessen better, do you have contraindications or suggestions about?
thanks for any answer

Since it works well in practice, no contradictions