01-13-2006, 11:40 AM
It depends what the noise sounds like- static crashes are often a bad tube.
I would first check the cathode bias resistor, #27- the 50K. If the bias on the AM detector is too low all sorts of noise will pass through.
The screen grid cap #31- .09 must stay in the circuit- it keeps the audio, RF, and IF signals from crosstalking to other tubes.
My only problem with the 70 is the audio distortion at higher audio levels; next time I'll buy a 90!. Good troubleshooting......
I would first check the cathode bias resistor, #27- the 50K. If the bias on the AM detector is too low all sorts of noise will pass through.
The screen grid cap #31- .09 must stay in the circuit- it keeps the audio, RF, and IF signals from crosstalking to other tubes.
My only problem with the 70 is the audio distortion at higher audio levels; next time I'll buy a 90!. Good troubleshooting......
Pete AI2V
