Problems with extra gain stage in 2203

[Wakculloch]

Just a thought, but have you decoupled your HT (Vb) supply to the stage. I've had problems in the past with cascaded stages coupling by positive feedback through the HT.

[HTH]

Just a thought, but have you decoupled your HT (Vb) supply to the stage. I've had problems in the past with cascaded stages coupling by positive feedback through the HT.

Not at present because it worked when I tried the extra stage at first, but I did consider that the extra stage was not sufficiently decoupled as I'm running three triodes from the same node.

I'll create a seperate node for the extra stage just to be sure - can't harm.

The unused side of the extra ECC83 is just simply not connected, i.e. the heater to that side isn't wired up.

[dai h.]

I've put the transformer in the same way as the stock one and also the same way as my '76 Superbass. That is, the primary side (plate leads) closest to the pots and the secondary side (speaker taps) closest to the output tubes.

hmm...well I looked at a couple of 100-watter chassis pics and I guess it's backwards to the wiring in the 50Ws(?).

the logic as far as the wiring is that I'm mentally picturing additional gain (from the gain increasing mod) equals more radiation (which can explain why moving wires can make it better or worse, i.e. moving one interacting with another to help induce problem oscillations can mean less capacitive coupling as well as putting flat against chassis = more capacitive coupling to ground plane = less capacitive coupling to another wire nearby), otherwise shielding (capacitive or electrostatic) shielding = blocking out/isolating. Worse as gain/volume control (plus tone controls) are turned up = more/less radiation of signal = more/less capacitive coupling.