Screen and PI Filter Resistors?

Get support and show off your MetroAmp 50 Watt kit builds.

Moderator: VelvetGeorge

Post Reply
revolver1
Senior Member
Posts: 511
Joined: Thu Jul 28, 2011 1:37 am
Just the numbers in order: 7

Screen and PI Filter Resistors?

Post by revolver1 » Tue Oct 31, 2017 3:43 am

Is it possible to put a 2watt 220k resistor between each of the terminals of the screen/pi can to ground?

Or just on the screen side?

Would this work like on the 100w amps?

Would it make the amp self draining?

Roe
Senior Member
Posts: 5054
Joined: Thu Apr 13, 2006 1:36 pm
Just the numbers in order: 7
Location: Drontheim. Norwegen
Contact:

Re: Screen and PI Filter Resistors?

Post by Roe » Tue Oct 31, 2017 5:35 am

yes, but the resistor should handle 500v or so. and it will change the preamp slightly. If you add a 220k bleeder at v1's filter cap, the ground potential of v1 is not any longer 1m with 1m vol pots, but rather 1m in parallell with 220k bleeder in series with the 100k plate resistor. the ground potential is then around a quarter of what it used to be.

I'd try two 220ks in series
http://www.myspace.com/20bonesband" onclick="window.open(this.href);return false;
http://www.myspace.com/prostitutes" onclick="window.open(this.href);return false;
Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39

Littlewyan
Senior Member
Posts: 200
Joined: Fri Dec 06, 2013 9:27 am
Just the numbers in order: 13492
Location: United Kingdom

Re: Screen and PI Filter Resistors?

Post by Littlewyan » Tue Oct 31, 2017 6:39 am

I never thought of it like that! Do you find that it changes the tone of the amp?

I use 270K 5W directly after the rectifier normally. The main reason for using 270K 5W is I have a bag of them and no other use for them!

Roe
Senior Member
Posts: 5054
Joined: Thu Apr 13, 2006 1:36 pm
Just the numbers in order: 7
Location: Drontheim. Norwegen
Contact:

Re: Screen and PI Filter Resistors?

Post by Roe » Tue Oct 31, 2017 9:37 am

yes, the effect is similar to using a 250k volume pot. I prefer the vol pot to read at least 500k. Lower reading pots can reduce noise and gain, something that can be useful on high-gain amps but hardly on plexis
http://www.myspace.com/20bonesband" onclick="window.open(this.href);return false;
http://www.myspace.com/prostitutes" onclick="window.open(this.href);return false;
Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39

User avatar
neikeel
Senior Member
Posts: 7231
Joined: Tue Dec 06, 2005 8:31 am
Location: Suffolk, England

Re: Screen and PI Filter Resistors?

Post by neikeel » Wed Nov 01, 2017 11:27 am

Roe wrote:
Tue Oct 31, 2017 9:37 am
yes, the effect is similar to using a 250k volume pot. I prefer the vol pot to read at least 500k. Lower reading pots can reduce noise and gain, something that can be useful on high-gain amps but hardly on plexis
Most agree that old plexis sound best with high reading >1M volume pots
Neil

Roe
Senior Member
Posts: 5054
Joined: Thu Apr 13, 2006 1:36 pm
Just the numbers in order: 7
Location: Drontheim. Norwegen
Contact:

Re: Screen and PI Filter Resistors?

Post by Roe » Fri Nov 03, 2017 2:17 pm

yes, another reason for being careful with those 56k screen bleeder resistors. 220k or 330k works well
http://www.myspace.com/20bonesband" onclick="window.open(this.href);return false;
http://www.myspace.com/prostitutes" onclick="window.open(this.href);return false;
Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39

Post Reply