Increasing gain on a CUSTOM 30

[andresound]

Hi guys,
Any ideas where I can increase gain of this circuit?

[sluckey]

Easy to try... Put a 22µF cap across the 1.5K cathode resistor. Change both preamp plate resistors to 220K.

[Tony Bones]

Might try increasing the 70k grid resistor (on the 3rd section, where the reverb mixes with the dry signal.)

[andresound]

Easy to try... Put a 22µF cap across the 1.5K cathode resistor. Change both preamp plate resistors to 220K.

The bypass cap was the first thing I did. I dropped input one 70k grid stopper to 33k and changed both plates on v1 to 220k. Improvement was nice.

[andresound]

Might try increasing the 70k grid resistor (on the 3rd section, where the reverb mixes with the dry signal.)

I haven’t tried this yet, but will do. Will this drive the PI harder?

Also thoughts on increasing the feedback resistor to 100k? This amp in original form was a very clean headroom type amp with minimal crunch even with HB’s. I have read, it is based on the Princeton/AC15 type style.

[andresound]

Easy to try... Put a 22µF cap across the 1.5K cathode resistor. Change both preamp plate resistors to 220K.

The bypass cap was the first thing I did. I dropped input one 70k grid stopper to 33k and changed both plates on v1 to 220k (should I not be changing the cathode resistors to 2.2/3,3k ?). Improvement so far is nice.

[Lynxtrap]

The 3M resistor between the reverb taps can usually be decreased, some people do this in Fenders (that have 3.3M res) and are happy with the result. 2.2M seems to be the most common substitute.

[andresound]

Gaining a LOT of knowledge from you guys, thank you!! Will change the 3meg. I am also going to up the 6.8k mid resistor in the tone stack to get a bit more mids. The v1a coupling cap is 45uf stock. I have brought that back down to 22uf in an attempt tame some bottom end.

I am well pleased with the results of the various mods so far. I am doing them one at a time, so I can hear what the mod does.

[Tony Bones]

Might try increasing the 70k grid resistor (on the 3rd section, where the reverb mixes with the dry signal.)

I haven’t tried this yet, but will do. Will this drive the PI harder?

Also thoughts on increasing the feedback resistor to 100k? This amp in original form was a very clean headroom type amp with minimal crunch even with HB’s. I have read, it is based on the Princeton/AC15 type style.

You can think of that resistor as the bottom part of a resistor divider. Increasing its value will present more signal to the 3rd stage.

Certainly try reducing the NFB. The 7189 can sound good with little or no feedback.

[andresound]

Might try increasing the 70k grid resistor (on the 3rd section, where the reverb mixes with the dry signal.)

I haven’t tried this yet, but will do. Will this drive the PI harder?

Also thoughts on increasing the feedback resistor to 100k? This amp in original form was a very clean headroom type amp with minimal crunch even with HB’s. I have read, it is based on the Princeton/AC15 type style.

You can think of that resistor as the bottom part of a resistor divider. Increasing its value will present more signal to the 3rd stage.

Certainly try reducing the NFB. The 7189 can sound good with little or no feedback.

Increased feedback to 100k and increased the 70k grid resistor to 150k. Amp certainly is “alive” now. I might have gone a bit too far . Will try in a band situation and revert. Will send gut pics this morning

[andresound]

Herewith gut pic and back in the cabinet