Tube DIY Asylum

Why not?

71.193.201.123

dogwan

In Reply to: RE: Yes, C5 and R14 are Zobel Network posted by FenderLover on November 29, 2009 at 14:00:00

What would be the repercussions if I did remove the Zobel network?

I'm tempted to try and see what the sound is like but don't want to blow anything up.

I've looked around at other schematics of similar PP designs and haven't found any that use a Zobel before the OPT. But I know I know only enough to get myself in trouble.

Follow Ups:

Don't remove for fear of damaging the output pentodes. - kurt s 16:00:55 11/29/09 (2)
This is not a Zobel network even though it looks like one. It is a resistive load so some load is always on this high output impedance tube. With no load and global NFB the output pentodes can overshoot and possibly oscillate at voltages above their voltage rating. So it is a dummy load for stability at all times and to protect the pentodes for when it's accidentally playing with no speaker plugged in.

Zobel networks would be for flattening average speaker loads combined, to be more resistive across the band to the pentodes. This is a 33K resistor load only, the cap is just a DC blocking cap and not a Zobel forming cap. The -3 dB point on the LF rolloff is down to 9.7 Hz. Not in band for the speaker load at all.

-Kurt
- RE: Don't remove for fear of damaging the output pentodes. - llwhtt 18:15:34 12/03/09 (1)
  I believe the correct term for an RC network in the primary of an OPT is "conjunctive filter". Seems to be a rather popular guitar amp tweek. Search the net for all of whys and wherefores.
  
  Craig
  - I learned something new. - kurt s 20:25:49 12/05/09 (0)
    I think you are right. I made a miscalculation anyway. It will cut down energy in the treble, not all the way to 10 Hz. I have made tricks like this in the input, but I see the advantage here is that when things go a little overload, this network can calm down the treble still for that "smoother" sound. Now I know a guitar amp trick.
    
    -Kurt

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