AC30CC2X

[Hojvaelde]

Hi
Here's something to think about for the specialists.

Subject: Defective Vox AC30CC2X

Error Description: The amplifier pops main fuse.

How:
I replace the fuse 2AT.
Power switch ON.
Standby switch OFF.
All the tubes begin to glow.
10-15 seconds later I see sparks inside rectifier tube,
and the fuse has blown again.
Note that it is without activating the standby switch.
The GZ34 is ca. 10 hours old

Benny

 

[JonSnell Electronic]

If the standby switch is in the off position, there is no AC return from the transformer so unless it has been modified, there is only a faulty GZ34 to consider.

 

[JonSnell Electronic]

Have you checked the schematic? There are many variations and thinking more into this, I did have an early AC30 in with the Standby Switch after the main smoothing. I would also check the main smoothing for leaks and short circuits.

 

[JonSnell Electronic]

http://bmamps.com/Schematics/vox/Vox_AC30CC2_AC30CC2X (2005) SM.pdf

 

[Enzo]

A tube that is new can still be bad. ANy tube can fail at any time.

 

[Hojvaelde]

Thanks all.

I did not know that there were / are several versions of the AC30.

I will just check the connection of the standby switch, and I will also check the connection on GZ34 tube. Pin 2 vs pin 8 issue.

There should just be noted that the previous tube held approximately 30 hours and this anything less.

There is also a fuse between the tube and the capacitors. It is the correct size and not blown.

Benny

 

[JonSnell Electronic]

GZ34s last for years in an AC30. In fact I changed one the other day in a 1962 model. 53 years of abuse, not bad!

 

[JonSnell Electronic]

Thanks all.

I did not know that there were / are several versions of the AC30.

I will just check the connection of the standby switch, and I will also check the connection on GZ34 tube. Pin 2 vs pin 8 issue.

There should just be noted that the previous tube held approximately 30 hours and this anything less.

There is also a fuse between the tube and the capacitors. It is the correct size and not blown.

Benny

Possibly a faulty GZ34.

 

[Tarzan]

Only from experience with new tubes:
JJ never failed since I use them for over a decade.
The stock tube in the AC30CC2 starts arcing within a short period of time.
But as said; That's my experience.

 

[gingertube]

Not an un-common problem.
There is a "standard" fix which relieves the reverse voltage stress on the tube rectifier.
Put solid state diodes in series with each tube rectifier anode feed. 1N4007 should do.
SS diode anode to the transformer lead, cathode to the rectifier tube anode. Do this on both tube rectifier anode connections.

These SS diodes then handle the reverse voltage stress reducing the likeyhood of arcing in the rectifier tube. You will still need to replace the rectifier tube which has arced but the new one should then be much happier.

Because these SS diodes are in series with the tube rectifier, SS diode switching noise is prevented from happening so any "garden variety" SS diode will do as long as its reverse voltage rating is enough. No need to use Ultra Fast Soft Recover diodes or anything special.

Cheers,
Ian