tube VCF

[Ken Stone]

Hi René and list,

>>I finished the tube portion of mine last night, and no doubt it has some
>>peculiarities due to the different tubes and transformer I used.
>
>What tubes did you use? 

An unmarked triode that in all likelyhood is a 6ES8/ECC189 and a 6064/CV4014
pentode. The former was on hand. The latter I bought 3 for $1.

>There is a trimmer in that schematic for this reason, but I ended up maxing
>out resonance too.

Actually, I have the resonance trimmer set to minimum resonance! The
behavior described was for this setting too.

>If you know the voltage ratings for the windings.

I didn't know the voltage ratings. I just used what I had to hand. Assuming
my measurements were correct, the transformer has a ratio of 60:9 or 6.66:1.
I back fed it with 15V and got 100v out, with the primary loaded with 1.5k.

>Thats about 50kOhms for the one I used.

About 25k for mine.

>Hm, I've got about the same, maybe a little less than in yours. 
>Most likely the gains of the individual stages V1b and V2 are different
>too, so that the grid of V2 sees a different voltage. I'd be interested to
>compare these figures.

I'll have to check this later. All the tubes are out at the moment, because
I've been working on it again. Hammers, chassis punches and tubes don't mix!

>Yes, when going beyond the point of selfoscillation very interesting things
>happen.

You did say it was "rewarding" when overdriven, though I wasn't expecting
that much of a reward.

>Btw: A neat addition would be to switch the filament to V2 on and off. (I
>noticed this when swapping tubes in the hot circuit...)

To ramp Q up and down? Perhaps we could even voltage control it? I'll have
to try it out.

Ken
_______________________________________________________________________
Ken Stone   sasami at blaze.net.au  
Catgirl Paradise <http://www.anime.net/~kens/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>