| 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. |
|
|
| 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 |
| quote: | 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 |
| quote: | | 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 |
| quote: | 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:smash: )
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....:rolleyes:
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 |
|
|
| aletheian |
| quote: | Originally posted by space-cake
i was thinking about building a small preamp using these but i would like to use 18V power supply. |
What is the reason for this? Is it the front end of a solid state circuit with an 18v supply available.. like a gainclone or something of that nature? Or is it battery powered? Either way ,you COULD consider a DC-DC converter to step it up a bit... they are getting much better these days. Mouser has some that i have tinkered with. You have to be a little clever to COMPLETELY eradicate the EMI, ripple and strange modulation artifacts, but with a good layout, a few filters and a regulator... it gets pretty good. I have not used them yet for low level audio supplies though... just modulation, RF etc.
There are a couple drop-in modules that are about half a cubic inch which are epoxy potted with a metal sheild that can step voltages up to 30 volts at a switching freq up above 200kHz, and there are a few to220 form factor chips that require a few more evternal parts that switch much higher than that and can give you close to 200v at a few dozen mA. | quote: | Originally posted by Alastair E
Ive found at these very low volts, that Michrophonics are non-existant for some weird reason... |
interesting.. that is good to know. I wish that there were accurate curves around of various tubes at low voltages and curents... and even my best spice models that i have slaved over are no good under a few mA at low voltages... the curves are too hard to model below that. |
|
|
| Alastair E |
There are a few commercial designs using Nuvistors at sub 30V....I guess when they were thought of, with the advent of transistors low volts operation was sort of built in.....
Ive tested the design above at 24V, and apart from a slight increase in gain, there is no other apparent difference in sound over 12V supply...:D |
|
|
| owen |
Thats because of the copious amounts of feedback used.. Should be pretty linear too.
Thats why you found little difference runnig at higher voltages.
The feedback is negative, and local, so minimises the 'feedback' loop - maximising the phase linearity of the stage...
An interesting choice.
Have fun
Owen |
|
|
| Alastair E |
Yes, there is huge amounts of local feedback. I sacrifice loads of gain, which for my use was fine. It started out life with a gain of around 15 which was too much for me anyway...
In the 'simulation' work I did it performed the best over all the other 'normal' tricks...
Phase-linearity if the simulator is to be believed (Which I dont!) is good for as low as 5Hz....
I does 'sound' pretty clean, neutral and powerful (For a pre-amp) Im quite happy with the results...
:D |
|
|
|
