leemhuis01,
I think I did not see the Actual, Complete, and Accurate schematic of your amplifier.
Is it in one of the posts in this thread?
I bet you have at least 3 low frequency poles . . .
1. EL34 cathode's bypass capacitors and the bias/balance resistors. (RC pole)
2. RC coupling from the driver to the EL34 (RC pole)
3. Output transformer primary inductance (output tube plates, rp, and L, Henrys) (RL pole)
2.75 Hz oscillation? (motorboating)
Negative Feedback and 3 pole LF phase and gain response. The 3 low frequency poles must have 3 different pole frequencies.
B+ with separate resistor and separate capacitor for each stage (enough filtering for no interference of one stage to the next stage)
I think I did not see the Actual, Complete, and Accurate schematic of your amplifier.
Is it in one of the posts in this thread?
I bet you have at least 3 low frequency poles . . .
1. EL34 cathode's bypass capacitors and the bias/balance resistors. (RC pole)
2. RC coupling from the driver to the EL34 (RC pole)
3. Output transformer primary inductance (output tube plates, rp, and L, Henrys) (RL pole)
2.75 Hz oscillation? (motorboating)
Negative Feedback and 3 pole LF phase and gain response. The 3 low frequency poles must have 3 different pole frequencies.
B+ with separate resistor and separate capacitor for each stage (enough filtering for no interference of one stage to the next stage)
The input g1 resistor is 1Meg Ohm. Why use such a high resistance?
What signal source are you using that can not drive a lower resistance, 47k Ohm for example.
With no input signal source connected, and no connection from the signal source (signal sources almost certainly have far less than 1 Meg Ohm output impedance) the amplifier might become an oscillator.
Any filament to cathode leakage from the 12AU7 input tube will cause 50Hz hum.
If your output transformer is different than the one on the schematic, it might cause:
Low frequency oscillation
And/Or
High frequency oscillation
Both negative feedback, and the low frequency poles may have to be adjusted.
There may be more problems, but you have to start somewhere.
What signal source are you using that can not drive a lower resistance, 47k Ohm for example.
With no input signal source connected, and no connection from the signal source (signal sources almost certainly have far less than 1 Meg Ohm output impedance) the amplifier might become an oscillator.
Any filament to cathode leakage from the 12AU7 input tube will cause 50Hz hum.
If your output transformer is different than the one on the schematic, it might cause:
Low frequency oscillation
And/Or
High frequency oscillation
Both negative feedback, and the low frequency poles may have to be adjusted.
There may be more problems, but you have to start somewhere.
