nuvistor bias with 18V ?

[space-cake]

does anyone knows how do i bias nuvistor tubes using a 18V power supply? 6CW4 type... thanks!

[ilimzn]

In general, very difficult as it normally works best with around 100V plate voltage. It would be possible to use a very low voltage such as 18V but the plate current would be very low. As for actual biasing, it depends on what you want to bias it for...

[space-cake]

i was thinking about building a small preamp using these but i would like to use 18V power supply.

[SY]

8056.

[space-cake]

well yes.... ecc86 would also be great but i have a few 6CW4 that i would like to use, i have tons of electronics parts left over from other projects and i wanted to use them to build a small preamp i could fit on my desktop.

[aletheian]

Originally posted by SY
8056.

NOOOOO> Don't tell him about those! I am hoping to buy them all up. I am tinkering in this area too

But yes, if you are set on a nuvistor, the 8056 will work much much better.

I don't know if you are set on nuvistors, but at that voltage, you can also look at space charge tubes, as was mentioned before, and a few subminis.

The space charge 12ae6 are popular in kits

A trioded CK512/CK6281 looks OK at 18v, etc.

even a 6922 will function. it is not nearly at it's best there, but MIGHT be better than a squirrly space charge tube or nuvistor.

[SY]

I am hoping to buy them all up.

I gave all mine away about a month or two ago. Nuvistors are horribly microphonic things. And not terribly linear. The 8056s were used as input buffers (very similar to the bootstrapped CF that Allen Wright uses) for Tek scopes due to their low noise and very low grid current. But that application was with 100% degeneration so the nonlinearity didn't matter much.

[aletheian]

Originally posted by SY


I gave all mine away about a month or two ago. Nuvistors are horribly microphonic things. And not terribly linear.

Awww... oh well. I'll keep eBaying. i have experienced the horrid microphonics, but I have them in mind for nonlinear and non audio applications actually.

[space-cake]

i keep hearing about the 8056, i asked about the 6CW4 since i have a few of them and i have no idea what i could build with them. but if we got onto the subject of 8056, does anyone have any audio circuits using them? i could not find anything on google.

[Alastair E]

Take a look at the scheme Ive been messing round developing a line-amp supplied with just 12V from some ideas given to me by a guy having trouble with a 'Tubalizer'....

It works best with the 7586 Nuvistor but the 6DJ8 as on the diagram works almost as well sonically Other valves Ive used are the 6/30fl2 and the 5786 computer valve. Even a 6SN7 works in this scheme, but lacks something....

Running the scheme at 18V will be fine, I doubt it will mean changing any bias, as at 12V the current is only around 600uA through the valves.

At 18V, the headroom will definately improve, as its a little limited for a gain of 4 running 12V and an I/P of 1V RMS....

Ive found at these very low volts, that Michrophonics are non-existant for some weird reason..I have used some 7586 Nuvistors that I know ring like bells at more 'normal' volts, these are perfectly quiet even if you hammer them with a spoon! (Not that Im in the habit of hammering valves with spoons )

The Russian 6C51-HB valve is very much lower in Microphonics than any American 7586 ive seen....

Im currently running Nuvistors in a breadboard, as I plan a line-amp to use with a TA2020 class T amp in the car....

The 6CW4 will work, but you may need to mess about as its a high Mu rather than the medium Mu valves that Ive used so will go into clipping much earlier