Slope resistor

5150loveeddie · Post by **5150loveeddie** » Fri Sep 10, 2004 10:39 pm

I've just swicht the slope resistor back to 33k (versus 56k) and my low ends are getting tighter.

Slope Resistor
The slope resistor is part of the tone network. It controls how the tone controls work. Also, the 33k slope resistor on these amps has a 500pf cap and the bass and plexis use 56k and 250pf. The 33k value (as opposed to 56k) has more gain in bass & mids. 33k also moves the resonant frequencies for the bass and mid tone controls slightly higher. You can even go to 16k for more bass and mid gain (and the overall frequency response flattens some). That came from: http://marshall.redpt.com/clay/marshall ... s_101.html (George's sticky post)

Since I've changed my board to the stock 68 PTP I was getting looser bass respond with a clean boost in front (ex. modern channel of the TMB didn't react well with the stock 68PTP...) but now it is getting much better but still a little mud on the low ends....

Any suggestions for that anyone???

Thanx

Flames1950 · Post by **Flames1950** » Fri Sep 10, 2004 11:49 pm

Refresh our memory: What were you finally running for feedback resistor and tap? And what output coupling caps did you go with, the .1uF or the later .022's? Still shared cathode?
To my ears, when I go with shared cathodes I don't feel the need to run the big .1uF's going into the power amp, for me I've got plenty of bass at that point and I need to keep it a little tighter, especially since I usually like the 100K feedback resistor off the four ohm tap for plenty of power amp gain.
Both my 50 watters are running as "mongrels" that way right now. Shared cathode 820ohm/330uF on V1, the lead tone stack (500pF, 33K slope resistor) and .022's in the output section. No bright cap on the mixer resistors, and only a 100-150pF bright cap on channel I. 100K feedback resistor on the four ohm tap with EL34's.

5150loveeddie · Post by **5150loveeddie** » Sat Sep 11, 2004 12:10 am

Negative feedback is on the 8ohms with the 48k

.1s for the output coupling caps (hummm I see what you mean here)

Shared cathode (stock 68 ptp except the slope resistor is back at 33k with the 500pf cap).

Flames1950 · Post by **Flames1950** » Sat Sep 11, 2004 7:28 am

Maybe give the .022's a try going into the power amp and see what you think. Your feedback is certainly more than mine, so you should be tighter there, although you could still try the 27K/16ohm tap combination as well.

5150loveeddie · Post by **5150loveeddie** » Sun Sep 12, 2004 12:15 am

Hey Flames I did reput the .022s in for the output coupling section and YES it is much much better now.........will now see for the BC330uf blue cap on the shared cathode.

Thanx