Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ClippIn4tae on September 30, 2017, 06:36:27 pm

Title: Question about dropping resistors rather than choke
Post by: ClippIn4tae on September 30, 2017, 06:36:27 pm

On  an ab763  style cicuit if not using a choke what resistor to use in its place?
 A 1k 3watt?

Title: Re: Question about dropping resistors rather than choke
Post by: tubeswell on September 30, 2017, 11:29:04 pm

1k works with 20uF cap in a BFPR to give 8Hz LF roll-off at the screen supply node, but the voltage drop is about 20V between the reservoir cap and the screen supply cap.  It would be a bit more in BFDR (2 x 6V6 screens, 2 x 12AT7s and 4 x 12AX7s going past this node), and more again in a 6L6-based amp etc.


With a 47uF smoothing cap, you could drop to 470R for the same frequency corner filtering, with less voltage drop.


A choke is 'better' because the smoothing is superior and the DC resistance is lower, leaving you with a tight DC supply with minimal loss of potential. But you might like the effect of a resistor, depends on what you want in terms of compression under high signal conditions etc