Issue with my '66 AC30

[zarc]

Hi everyone

I am posting here, hoping for your help concerning the issue I have with my 1966 Vos AC30.

The problem is as follows
- sound on "brillant" channel is thin and has a very heavy distorsion (this being true on both inputs), while it is perfectly ok on the 2 other channels
- when I switch on the amp (no stand by on these old Vox, only one on/off switch), sound comes after about 10s on "normal" and "vibrato" channels while it takes about 1 minute to get some (awful) sound on the brillant channel. There is nothing before that.

Here is a recording to give you an idea of what happens. When the sound is ok I am on the normal channel
https://soundcloud.com/user-417771443/ac30

Do you have any idea what the problem could be?
I changed all preamp tubes without any result, and power tubes where changed a few years ago.

Many thanks in advance for any help you could provide me with!

[Chuck H]

Sounds like there may be a fault in the Brilliant circuit supply voltage or signal path or there may be a leaky film cap skewing bias on a triode. You're going to need to open it up and take/interpret measurements in either case.

[shortcircuit]

Hi everyone

I am posting here, hoping for your help concerning the issue I have with my 1966 Vos AC30.

The problem is as follows
- sound on "brillant" channel is thin and has a very heavy distorsion (this being true on both inputs), while it is perfectly ok on the 2 other channels
- when I switch on the amp (no stand by on these old Vox, only one on/off switch), sound comes after about 10s on "normal" and "vibrato" channels while it takes about 1 minute to get some (awful) sound on the brillant channel. There is nothing before that.

Here is a recording to give you an idea of what happens. When the sound is ok I am on the normal channel
https://soundcloud.com/user-417771443/ac30

Do you have any idea what the problem could be?
I changed all preamp tubes without any result, and power tubes where changed a few years ago.

Many thanks in advance for any help you could provide me with!

Can you post a schematic ?

[zarc]

Sounds like there may be a fault in the Brilliant circuit supply voltage or signal path or there may be a leaky film cap skewing bias on a triode. You're going to need to open it up and take/interpret measurements in either case.

Thank you Chuck.
Yes, I guess it does not come from the tubes

Can you post a schematic ?

It is a mid 60's Top Boost AC30.
I will try to get you that