5150 mod question

[Danglin' Fury]

Recently got a 5150 on the bench... dude said his presence and Resonance went screwy while playing... fixed that, but it had a couple of mods done and I was curious about one of them. Dude bought the amp that way... there is a bias pot mod that looks pretty good... nicely done.... there are bypass wires on R18 and C17...the R18 one I get, they are passing more of the signal to ground to "tighten up" the amp... but what is the purpose of bypassing C17? Thanks in advance for looking...

[Dave H]

there are bypass wires on R18 and C17...the R18 one I get, they are passing more of the signal to ground to "tighten up" the amp... but what is the purpose of bypassing C17? Thanks in advance for looking...

It looks like they were trying to increase gain (does it need more gain?) Shorting R18 increases the gain of V1B by bypassing its cathode resistor with C26, A job already done by K1A in the position shown. shorting C17/R29 increases the low frequency gain.