Quote:
Originally Posted by Notimetolooz
The voltages you measured around the 6K6 seem pretty good. Have you tested and replaced tubes in this set?
What about the voltages on the 6AT6 pins.
A bit of clarification on how the sound stages work. 6K6 is the audio output tube, it is responsible with developing the power to operate the speaker. Most of the 6AT6 is used as a audio amplifier, it increases the voltage size (amplitude) of the audio signal. The 6AL5 is the FM discriminator (detector or demodulator). Before the 6AL5 the signal is 21.25 MHz with FM audio modulation, after the discriminator the sound is in the audio range. That makes the volume control a good place to try injecting audio. The audio stages are easier to troubleshoot than the IF.
You need a bigger audio signal at the grid of the 6K6 than the 6AT6 grid to hear the same volume.
The general way to determine the wattage required for a resistor is to use the resistor value and the voltage difference across it. That 1K resistor that feeds the screen of the 6K6 and then feeds the plate through the output transformer has 25 volts across it. Voltage squared, divided by the resistance is the wattage given off (dissipated), that come out to 0.625W. You always want to use a resistor rated two or more times the dissipated wattage so it stays fairly cool. So a 2W should be OK.
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I fed an audio signal through the grid of the 6AT6 and the sound system from there forward works...speaker, AO transformer and tube and the volume control. I fed a 21.5 MHz RF signal through the plate for both pin 2 and 7 of the 6AL5 and didn't get a signal through the speaker with either. Am I doing something wrong here? I tried about 4 different 6AL5s but nothing changed. I'm sure I'm doing something stupid!
