Page 1 of 1

Fixed bias through Superpermalloy TVC

PostPosted: Sat Jan 10, 2009 12:55 pm
by revintage
Hello Brian,
Found out you had a new forum so I add the same question as in your old.

Bought your TVCs about a year ago and they work splendid.

Got the idea to rebuild my 6N30P parafeed preamp with fixedbias through the TVC.

Technically/theoretically it shouldn´t be any problems as long as no grid current is drawn.

Do you see any?

Brgds
Lars

Re: Fixed bias through Superpermalloy TVC

PostPosted: Fri Jan 16, 2009 7:08 am
by brian
Hi Lars
I didn't respond because I'm having difficulty visualizing the circuit. Are just using it as a grid choke? OK but seems a waste.
If still controlling signal input, bias will change as volume changes.
Do you have it rawn out? Maybe post it and others will put in their 2 cents as well.
Brian

Re: Fixed bias through Superpermalloy TVC

PostPosted: Fri Jan 16, 2009 6:01 pm
by revintage
Does this make things clear? There is anyway no chance for bias to change due to volumechange as there is no current drawn from the grid. R2 can be much higher(say 1Meg) not to load the secondary and is necessary if the switch should lose contact. Bias in this case ca -10V. -12V is already there as it is used for the heaters.

Lars

Re: Fixed bias through Superpermalloy TVC

PostPosted: Mon Jan 19, 2009 7:29 am
by brian
Ok, picture worth a 1000 words.
It looks to work as you say, but I've no experience with it. Why not drop it into DIYaudio tube forum? Likely draw a wider range of experience.
Would be interested to know how it turns out, if you try it.
Brian

Re: Fixed bias through Superpermalloy TVC

PostPosted: Mon Jan 19, 2009 2:54 pm
by revintage
Hi again,
Got an E-mail from one of the authorities in this field, who had read the thread in audioaylum. It should work, but bias should consist of seriesconnected 3V lithiumcells(not rechargable). This makes the circuit even simpler. See attachment.

Brgds
Lars