TLK
New member
Anybody knowledgeable on the Altec "Coke Bottle" microphone ? Working on one for a friend that has no output. Been thru the 518A power supply, checked all the passive components, resistors and caps.
Caps all check ok, there is some minimal hum on the audio output, but DC outputs are certainly clean enough to at least two power the mic All DC power supply output voltages are within the ranges shown on the schematic, however the mic itself seems to be the problem. Only components in the mic is 6AU6 tube, 8 pin Cannon connector and the small dime sized screw on capsule. No other components in the mic. The tube is operating properly and amplification is evidenced with capsule removed by touching the center pin that contacts the capsule.
I know this super hi-Z circuitry is tricky to trouble shoot.. Without the capsule installed, charging voltage at outer spring loaded contact at base of capsule is about 180 VDC. With capsule installed, that voltage appears be loaded down by the capsule to somewhere around 11 volts. What is the correct dc voltage required to charge the condenser capsule ??? From what I see on the schematic should be a fairly high voltage. It seems like the capsule is somehow defective. Checking the capsule itself shows no shorts or any resistance resistance, however the voltage drop when installed would suggest otherwise.
Any assistance would be most appreciated...
Caps all check ok, there is some minimal hum on the audio output, but DC outputs are certainly clean enough to at least two power the mic All DC power supply output voltages are within the ranges shown on the schematic, however the mic itself seems to be the problem. Only components in the mic is 6AU6 tube, 8 pin Cannon connector and the small dime sized screw on capsule. No other components in the mic. The tube is operating properly and amplification is evidenced with capsule removed by touching the center pin that contacts the capsule.
I know this super hi-Z circuitry is tricky to trouble shoot.. Without the capsule installed, charging voltage at outer spring loaded contact at base of capsule is about 180 VDC. With capsule installed, that voltage appears be loaded down by the capsule to somewhere around 11 volts. What is the correct dc voltage required to charge the condenser capsule ??? From what I see on the schematic should be a fairly high voltage. It seems like the capsule is somehow defective. Checking the capsule itself shows no shorts or any resistance resistance, however the voltage drop when installed would suggest otherwise.
Any assistance would be most appreciated...
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