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Author Topic: Airline JDR 8439  (Read 1841 times)

memoryman

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Airline JDR 8439
« on: August 13, 2015, 02:21:10 AM »
A signal will pass through three jacks marked "Sting Instruments" in the center but the others to the right marked "Microphone Accordion" will not pass a signal. The Vibrato/tremolo does not work and I am not sure if the jacks labeled so are for foot switch or for an instrument. What should I try first ? I hope the schematic is close, if anyone has a better one please post it. I believe that this is a 1955 Wards Danelectro amplifier.
« Last Edit: August 13, 2015, 02:46:29 AM by memoryman »

Vitrolin

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Re: Airline JDR 8439
« Reply #1 on: August 13, 2015, 03:38:25 PM »
When you say "a signal will pass through" is it measured with oscilloscope or heard through the speaker?

If you do not have an oscilloscope i would replace the 12ax7 with one that is known to be good.

or:

If you heard sound from instrument channel and not from the mic channel, then everything after the phaseinverter is good, or good enough.
Take an audio probe (a coax cable with a multimeter test probe in one, end and two hooks or clamps in the other end, for signal and one for ground/screen, and a capacitor in the signal path for picking ip audio with a DC offset)

Connect hooks to groung and instrument channel volume pot, apply signal to mic/acc channel and follow this signal path with test probe end.

Use a multimeter test probe with a short pin or insulate it so max 4mm are exposed, limits the possibility for making a short cuircuit.

Usual disclaimer tubes=high voltage=fire death and destruction