Vox vt50 & vt100

[J M Fahey]

Build and use a lamp bulb limiter, it's a mess when you replace power transistors or an expensive IC and due to some minor problem which you didn't see it burns again on turn on.

Only *after* it turns on without speakers connected nor any other load can uou carefully connect speakers again and play a little.

And those speakers are dead because somebody heard a loud hum and did NOT turn the amp OFF immediately nor disconnect speakers while he started turning knobs trying to silence it .

[tbonuss]

Ah, yes. Will do.

[tbonuss]

Made a lamp bulb limiter from a drop light and then rewiring the outlet, light and switch in series. 15 bucks at Home Depot. Not sure that is the most cost effective, but it looks clean, and works great!

So...No more DC voltage on the speaker wires or external speaker out and headphones still sound good.
Plugged in a speaker to the external speaker out...works, but low power / high distortion which kind of fades in and out.

Dadgummit. Well at least the drop light limiter was cool.

[Jazz P Bass]

Uhm.

Don't run the amp into a speaker with the limiter in place.

[tbonuss]

Yes. I didn't--sorry, I should have made that clear.

[tbonuss]

Here is a link to download the VT50
http://bmamps.com/Schematics/vox/Vox_vt50_sm.pdf

What specific symptoms/problems are you experiencing with the VT100?

Edit: please refer to this post for VT100 schematics. (Note: there is a claim that perhaps the AD100vt is similar to the 100vt output)
http://music-electronics-forum.com/t31986/

AD100vt schematic. I have not worked on 100vt or AD100vt so I am really not sure if the output section is even close to each other...
http://bmamps.com/Schematics/vox/Vox...e%20Manual.pdf

On the parts of the circuit that I have physically looked at, it is not similar (in my mind) to the AD100VT schematic. Maybe someone who is more familiar with guitar amps would see similarities, but as far as the section I looked at, it is different enough to be of no use to me personally.

The VT50 is somewhat similar, but has a different IC and I noticed some different values on resistors and P/S voltage--it helps conceptually to understand what the idea of the circuit is, but not close enough for me to do the math on anticipated voltage readings.

If someone sees it differently, I would be interested to hear a different perspective.

[tbonuss]

Okay--I've totally made a mess of this thread.
1. The VT50 is similar to the VT100, and in some places identical (although almost all the component labels are different).
2. The AD100VT is not (at least the part that I physically looked at on the board).
3. Since this thread is in the schematics section, I have created a new thread to talk about my troubleshooting / repair issues for my VT100.

I apologize for my sloppiness.