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Hi, Guys. I have a vox vt 30 combo with no sound from speaker,but all works ok through headphones. The only circuit diagram I have is for
the ad30vt which is similar but there are a fair bit of circuit changes to the later vt30.With the preamp and power supply/output pcbs removed,
I checked when phone jack removed,the mute line is disabled from the output chip [ tda 2050 ] and probing pin 1 of ic produces a buzz,so output
chip is ok There is a buzz which varies with the power level control,but tracing back from there is tricky because the component reference numbers
on the vt30 pcb are all different from the ad30vt. The vt30 uses two 9v reg ics ,where as the ad30vt has two 15v regs. Has onyone got even just
output circuit of this amp showing the signal path thro ic6 and ic20. Probing pin 1 of ic6 producing a buzz. sound can be picked up also on the two
grids of the 12ax7 valve,when a sound source is connected to input socket. Pins 1 and 6 [ anodes] of 12ax7 has 23v. cathode pins 3 and 8 are about 3v.
As I say all tone controls and reverb etc are all working fine thro headphones. See attached pics of pcb.
Many thanks, Byronboy.
the ad30vt which is similar but there are a fair bit of circuit changes to the later vt30.With the preamp and power supply/output pcbs removed,
I checked when phone jack removed,the mute line is disabled from the output chip [ tda 2050 ] and probing pin 1 of ic produces a buzz,so output
chip is ok There is a buzz which varies with the power level control,but tracing back from there is tricky because the component reference numbers
on the vt30 pcb are all different from the ad30vt. The vt30 uses two 9v reg ics ,where as the ad30vt has two 15v regs. Has onyone got even just
output circuit of this amp showing the signal path thro ic6 and ic20. Probing pin 1 of ic6 producing a buzz. sound can be picked up also on the two
grids of the 12ax7 valve,when a sound source is connected to input socket. Pins 1 and 6 [ anodes] of 12ax7 has 23v. cathode pins 3 and 8 are about 3v.
As I say all tone controls and reverb etc are all working fine thro headphones. See attached pics of pcb.
Many thanks, Byronboy.
Attached Files