Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Tubes and Hybrids => Topic started by: memoryman on August 13, 2015, 02:21:10 AM

Title: Airline JDR 8439
Post by: memoryman 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.
Title: Re: Airline JDR 8439
Post by: Vitrolin 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