Problems with AC30 tbx standby/rectifier/fuses

[robojim4000]

Last week, when using the original tubes i switched my AC30 off standby and it just died, i changed the main fuse, which had blown, as well as a new rectifier tube...

It worked well for a week, until today, where the amp would not come off standby (red light on, no orange light) - i noticed the rectifier tube was not lit, but all the others were. I jingled the rectifier clip around a bit, and poked it with a plank of wood, and it lit up, it seems as if it was very temperamental to how i placed it....

However, then when testing the standby switches and just generally seeing how reliable it was to turn on/off - it suddenly went crazy, purple lights in the rectifier, pretty scary. It blew the HT fuse

Why was the rectifier going crazy, its new!?
Why was it so temperamental to where it was positioned?

hmm, also, just noticed this. One of the red wires coming from the rectifier socket is not where it is on other examples, does this matter? ... check out the pics...

[robojim4000]

heres the schematic for it... the rectifier is at the bottom in the middle... does it match up to my pic?

http://www.schematicheaven.com/voxamps/ac3093pa.pdf

[pdf64]

I can't see the locating keyway on the socket, but in my reckoning, Ex1 and 2 are correct, yours is wired incorrectly. I think think the manufacturers sent a load of them out like that.
The problem with wiring them like yours is that all the B+ current goes through the rectifier heater, which can't cope with surge currents of charging up the reservoir cap when switching standby on and off. Plus the 5VAC is added to the B+ ripple.
It's a hidden fault because it works but causes premature rectifier failure.
Much better not to use standby at all, as the rectifier naturally will ramp the B+ voltage up slowly as it powers/warms up. Peter.

[Eltek]

Hi robojim4000,

http://pdf1.alldatasheet.com/datashe...LIPS/GZ34.html

As pdf64 says, probably your rectifier tube is wired incorrectly. At he link above, you can check the pinout of the GZ34. Then find out which is the pin8 of the tube and solder the RED wire to that pin. If you are lucky enough, yout OT and output tubes survived the adventure...

Have fun,
Ivan

[robojim4000]

I can't see the locating keyway on the socket, but in my reckoning, Ex1 and 2 are correct, yours is wired incorrectly. I think think the manufacturers sent a load of them out like that.
The problem with wiring them like yours is that all the B+ current goes through the rectifier heater, which can't cope with surge currents of charging up the reservoir cap when switching standby on and off. Plus the 5VAC is added to the B+ ripple.
It's a hidden fault because it works but causes premature rectifier failure.
Much better not to use standby at all, as the rectifier naturally will ramp the B+ voltage up slowly as it powers/warms up. Peter.

cheers for the help guys. I can confirm my red wire is definitely coming out of pin 8. But on the other examples it seems to come out of pin 2, along with the black wire that goes off to the other fuse.

Whats the best thing to do, leave it as it is and dont use standby, or solder the red wire to pin 2 rather than pin 8 (as in example 1 and 2?)

[robojim4000]

one last bump?

[pdf64]

Pin 8 is correct, don't move the red wire to 2.
Best not to use the standby switch, or to move where it is to after the reservoir cap (so the cap is on the hot side of the switch). But that might not be simple on a PCB amp. Maybe you just got a bad tube. Peter.