Vibra-Champ AA764 question

[Paul]

Hi,

Am working on an old blackface champ. I have a question about
the output however.

When the output is attached to an 8ohm dummy load and I input
a sine wave, the output wave has a positive peak of about 9V and
the negative peak clips at about 5V. The sine wave is good going
into the 6V6, the clipping is happening on the output of the 6V6.

Anyone have an idea of what might be happening here or what I
should expect to see on the output?

Thanks in advance,

--Paul T.

[Bruce / Mission Amps]

Hi,

Am working on an old blackface champ. I have a question about
the output however.

When the output is attached to an 8ohm dummy load and I input
a sine wave, the output wave has a positive peak of about 9V and
the negative peak clips at about 5V. The sine wave is good going
into the 6V6, the clipping is happening on the output of the 6V6.

Anyone have an idea of what might be happening here or what I
should expect to see on the output?

Thanks in advance,

--Paul T.

You are probably driving the tube so hard it is going into class B on the other cycle.
Most of those amps, when bone stock, will not even make an honest 2.5 to 3 watts... clean.
For sake of argument, if you are driving the load to about 6.5vac, (rms) your output power would be 5 watts. This is unlikely in that amp so I can only assume you are looking at a 9v peak where the signal is already massively distorted.

[Paul]

Vibra-Champ AA764 question

>You are probably driving the tube so hard it is going into class B on the >other cycle.
Yes, am overdriving it in that state...

>Most of those amps, when bone stock, will not even make an honest 2.5 to 3 >watts... clean.
Ah, I was wondering about that..... I am able to get 2w rms of clean signal.
So I guess it is normal for this amp to go into class B or AB when overdiven
and is part of it's distinctive 'sound'

I was hoping to get a little more clean power out of it.

Thanks!

--Paul T.

[Bruce / Mission Amps]

>You are probably driving the tube so hard it is going into class B on the >other cycle.
Yes, am overdriving it in that state...

>Most of those amps, when bone stock, will not even make an honest 2.5 to 3 >watts... clean.
Ah, I was wondering about that..... I am able to get 2w rms of clean signal.
So I guess it is normal for this amp to go into class B or AB when overdiven
and is part of it's distinctive 'sound'

I was hoping to get a little more clean power out of it.

Thanks!

--Paul T.

Yup, I think that amp is operating normally... I don't think it can go into class AB though, as I was always under the impression that is a designation for two power tubes in push pull.
It has to shove the grid so hard on one side of the sine wave (into class B) and shut off for part of the cycle, I think that is what you are seeing.