Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tubenit on February 09, 2012, 06:06:40 am

Title: What's happening here?
Post by: tubenit on February 09, 2012, 06:06:40 am

I've not seen a cathode cap/resistor set up like this before?  Anyone know what's going on with this?

With respect,  Tubenit

Title: Re: What's happening here?
Post by: LooseChange on February 09, 2012, 06:33:52 am

Yes you have. Look at half of a long tail PI.
It provides fixed bias to the tube.

Title: Re: What's happening here?
Post by: John on February 09, 2012, 06:39:00 am

What are the advantages to that over the simple cathode bias we normally see on preamp tubes?

Title: Re: What's happening here?
Post by: Colas LeGrippa on February 09, 2012, 07:09:58 am

the last section to ground ( 3.9k / 2,2uF ) is a typical low-pass filter arrangement

Title: Re: What's happening here?
Post by: PRR on February 09, 2012, 09:46:41 pm

> low-pass

At 18Hz. Won't affect small-signal response. Might be overload-recovery timing. Might be a waste of 3 small parts.