Hi everyone,
I am currently servicing an AC30 / 6TB wich is kind of impertinent.
Long story made short, it's a double side PCB and it had an electric arc between +HT and a tube heaters power raíl through a capacitor leg (C46) . It blew the choke and the fuse.
After it, the amp has been recapped and a new 30H 100mA choke has been fitted. Also, I have mount this part of the circuit out of the PCB (P2P) and added another fuse to protect the choke.
Also, I have added a Pot to balance the power tubes. Without the inverting tube (V6) you can tune the power tubes to be dead quiet using "unmatched tubes".
With inverting tube fitted it has an audible "spike noise" wich seems to be generated in the "Normal Channel" between C11, R58 and the tube. The spikes are not before R58 , and no spikes on either side of R57 (Brillant Channel) . With the tube pulled out and R58 lifted, spikes are also there. Even with the tube socket pulled out spikes are there...
The noise varíes with the Normal potentiometer. The noise is there with the potentiometer at Min and at Max, but dissappears at mid position, it seems to cancell out.
When in Stand-By mode, the AC line of the tube heaters is a nice and beautiful sine wave, but when is turned ON, the wave gets squeezed.
Has anyone experienced symptoms of conductive PCB's..??
Thanks..!!
AC30 Top Boost schematics :
Pre : http://www.blueguitar.org/new/schem/vox/ac30ripr.jpg
Power amp & PSU : http://www.blueguitar.org/new/schem/vox/ac30ripw.jpg
I am currently servicing an AC30 / 6TB wich is kind of impertinent.
Long story made short, it's a double side PCB and it had an electric arc between +HT and a tube heaters power raíl through a capacitor leg (C46) . It blew the choke and the fuse.
After it, the amp has been recapped and a new 30H 100mA choke has been fitted. Also, I have mount this part of the circuit out of the PCB (P2P) and added another fuse to protect the choke.
Also, I have added a Pot to balance the power tubes. Without the inverting tube (V6) you can tune the power tubes to be dead quiet using "unmatched tubes".
With inverting tube fitted it has an audible "spike noise" wich seems to be generated in the "Normal Channel" between C11, R58 and the tube. The spikes are not before R58 , and no spikes on either side of R57 (Brillant Channel) . With the tube pulled out and R58 lifted, spikes are also there. Even with the tube socket pulled out spikes are there...
The noise varíes with the Normal potentiometer. The noise is there with the potentiometer at Min and at Max, but dissappears at mid position, it seems to cancell out.
When in Stand-By mode, the AC line of the tube heaters is a nice and beautiful sine wave, but when is turned ON, the wave gets squeezed.
Has anyone experienced symptoms of conductive PCB's..??
Thanks..!!
AC30 Top Boost schematics :
Pre : http://www.blueguitar.org/new/schem/vox/ac30ripr.jpg
Power amp & PSU : http://www.blueguitar.org/new/schem/vox/ac30ripw.jpg