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CDA · 3rd March 2009

You don't need a filter and you don't need a new amp.

Your amp is old as hell (Which is good imo) and needs some service.

Have you noticed if the gain on the amp has shot up, or down...

First place I would check is the cathode bypass caps. These go bad, and cause all sorts of problems.

Your cathode resistor is usually around 820 ohm to maybe 3.3k

This resistor is paralleled by a capacitor. Usually a 25uf 25v for Fenders, and a .68uf for Marshals (That's why they sound different people)

Anyways, these go bad. It can cause hum, low gain, high gain (Hissing) etc etc

So, add all this up with other failing components and you get what you have here. Noise and undesirable performance.

I'm sure your decoupling caps are passing DC to the next stages which will throw the circuit out of whack.

3rd March 2009	#6
CDA Gear maniac Join Date: Jan 2009 Posts: 236	You don't need a filter and you don't need a new amp. Your amp is old as hell (Which is good imo) and needs some service. Have you noticed if the gain on the amp has shot up, or down... First place I would check is the cathode bypass caps. These go bad, and cause all sorts of problems. Your cathode resistor is usually around 820 ohm to maybe 3.3k This resistor is paralleled by a capacitor. Usually a 25uf 25v for Fenders, and a .68uf for Marshals (That's why they sound different people) Anyways, these go bad. It can cause hum, low gain, high gain (Hissing) etc etc So, add all this up with other failing components and you get what you have here. Noise and undesirable performance. I'm sure your decoupling caps are passing DC to the next stages which will throw the circuit out of whack.