Ampeg VT-40 fuse ?

[Oldsoul]

I'm a little confused. I just picked up a not working VT-40. Most all original caps. Output tubes changed to EL-34s which were toast. There was a sticker on the amp from a tech who made the mod. Most all filter caps original. There is also a fuse attached to the fuse holder the extra AC outlet. The schematic shows a 6A 4A fuse and a circuit breaker. What is that? Mine just has a fuse holder. Should this fuse be 6 or 4 amp? Also is the additional fuse original?

[Leo_Gnardo]

I just picked up a not working VT-40. -snip- There is also a fuse attached to the fuse holder the extra AC outlet. The schematic shows a 6A 4A fuse and a circuit breaker. What is that? Mine just has a fuse holder. Should this fuse be 6 or 4 amp? Also is the additional fuse original?

Ampegs late 60's thru the 70's often had a second fuse inside the amp, in series with the fuse in the fuseholder. The idea was, if some bright spark replaces the fuse - in the fuseholder - with a hi value fuse, piece of wire or foil, then hopefully the interior fuse will open before the transformer(s) are wrecked. At that point a trip to the repair shop should prove obviously necessary.

Can't say I've seen a circuit breaker in an Ampeg but they may have tried that at some point. It's ordinary practice to not fuse the "convenience outlet" but maybe someone thought it a good idea to do so.

4 amps is more than enough to run a VT-40. Heck even 3A slo blo should be plenty.

If it was up to me I'd simplify the fusing arrangement, and just have the one in the fuseholder, especially if it was my own amp.

[g1]

Maybe you are looking at the wrong schematic? The schematic that shows the circuit breaker has a control called "distortion", does yours have that?
The older versions have a back-up fuse in series with the fuse holder. It is not for the AC outlet. It is supposed to blow if the amp has a problem and someone puts tinfoil over the regular fuse.

[Enzo]

There are several versions.


Ampeg used to put a fuse inside as well as the one in the holder outside. The one inside would be a pigtail fuse - the kind with wires out the ends and soldered in. The internal fuse would be like one amp larger than the one in the holder. This was done so that if someone blew the 4A fuse, they couldn;t just stuff a 30A fuse from their car into the holder. There would still be that inner fuse protecting things.

I have a couple schematics for this model. One shows a breaker on;ly, and it says 4A and 6A next to it, but there is also a star, and if you look down in the schematic notes section the star tells you the parts with the star are only on the V4 and VT22 models, so it looks like the 4A breaker for you.

[g1]

Here is the version without the distortion circuit or the circuit breaker.
The external fuse in the holder is 4A, the back-up fuse inside is 6A.

[Oldsoul]

WOW you guys are awesome. My model does have the Distortion. Attached is a scan off the top of the amp. The fuse that was blown was indeed one with soldered leads attached to it.

[drewl]

I've heard they put a fuse on the inside to prevent idiots from using one too large on the outside


Just replaced the inside fuse on a V4, you should see how some people try to wire/solder those inside fuse replacements!