New 183 build

[Stephen1966]

V1 is not likely to be a problem for "distortion" if is middle biased (see the voltages in cathodes for V1a-V1b),

Probably you are refferencing to too much bass in the clean channel or too much bass going to the PI, where values of some caps need to be reduced.

To attack this, you can lower the value of the cap in the PI (positioned on second grid to gnd) from 0.1uF to 22nF and then check again, and lower values to input to the PI 22nF to 1nF (for checks only)

'...referencing too much bass...' Hmm... It's true, it's been a bassy amp ever since it was first switched on. It's a narrow band of bass distortion, I don't get it on the fifth string... I can at least rule out the overdrive at this stage since it wasn't engaged when I heard the farty low notes. I have to do some more investigating, and thanks, I'll check those voltages again. Before I think about changing any components values though I will run the preamp through my 124(ish) Skyliner power section and then vice versa, run the Skyliner's preamp through this amps power section. That and run the speaker cab off the Skyliner alone as well. This way, I should be able to narrow down where the fault is occurring.

[Stephen1966]

Getting ready to hook up the second amp to test thing out and I play the same thing again and the distortion is gone. I think it was my thumb that was distorting Anyway, I will have another go at it later and see if I missed anything. Have to say, I think it's more likely to be my playing than the circuit. Not swapping anything until I'm sure. Sounds great from Jazz cleans to hard rock.

[WhopperPlate]

Getting ready to hook up the second amp to test thing out and I play the same thing again and the distortion is gone. I think it was my thumb that was distorting Anyway, I will have another go at it later and see if I missed anything. Have to say, I think it's more likely to be my playing than the circuit. Not swapping anything until I'm sure. Sounds great from Jazz cleans to hard rock.

Keep an eye on that wall voltage when considering variables …

…also consider what times of day you are playing …mains electricity can be a can of worms of complicating factors that can potentially induce tonal inconsistency.

[Stephen1966]

Getting ready to hook up the second amp to test thing out and I play the same thing again and the distortion is gone. I think it was my thumb that was distorting Anyway, I will have another go at it later and see if I missed anything. Have to say, I think it's more likely to be my playing than the circuit. Not swapping anything until I'm sure. Sounds great from Jazz cleans to hard rock.

Keep an eye on that wall voltage when considering variables …

…also consider what times of day you are playing …mains electricity can be a can of worms of complicating factors that can potentially induce tonal inconsistency.

Good point. I never heard the problem when I ran it off the variac and wall voltages swing big here... I need to keep trying it at different times of day as you say.