.0047 vs.022 PT grid couplers

[daz]

Can anyone tell me at what frequency the signal would drop off at using .0047uf as the coupling caps from the PI to the power tubes vs the .022's i had b4 ? I tried this and it sounded good till i did a NYE gig with it and it was somewhat thin sounding. (god i hate how you just can never tell at home what will happen at a gig) I realize it's like 1/4 the value of the .022's, but still i'm curious what at frequency the drop off starts with that value.

[Joey Voltage]

Can anyone tell me at what frequency the signal would drop off at using .0047uf as the coupling caps from the PI to the power tubes vs the .022's i had b4 ? I tried this and it sounded good till i did a NYE gig with it and it was somewhat thin sounding. (god i hate how you just can never tell at home what will happen at a gig) I realize it's like 1/4 the value of the .022's, but still i'm curious what at frequency the drop off starts with that value.

It really depends on a couple of things. The output impedance of the PI, and the load as well, to just throw out some quick calculations 38K output impedance, and a typical 220K load about 131hz roll off with the .0047uf's

[daz]

That actually sounds about right as far as what it sounded like to me...like it started rolling off around 100Hz.

[Joey Voltage]

That actually sounds about right as far as what it sounded like to me...like it started rolling off around 100Hz.

Just out of curiosity, what amp have you done this with

[daz]

One i built. It's not any particular design, but it's got a cathode biased EL34x2 output with switchable NFB and PI values like a typical marhall

[Guitarist]

I've found that .0047 woks great with dirty channels; that 100Hz roll-out keeps the riffs fast and tight.