Ampeg V4B

[selloutrr]

That schematic is pretty good.

The V4-B is an early (non-distortion) model V4 (or VT-22) minus the reverb section and with the added Ultra-Low switch and RC network. Otherwise they are the same.

CORRECTION: THE V4B is the BASS version of the V4,VT-40,VT-22. Come versions depending on the time they were built use different tubes and layouts.

[selloutrr]

becareful solding on the PCB this era of Ampeg PCB's traces tend to peel up if they are over heated... or looked at the wrong way.

[Luthierwnc]

I'll second the PCB trace advice. They peel up easily. Use wick and be sure the connection is as de-soldered as possible before you pull the component.

One more caveat, V-series amps are very touchy about their star grounding system. On the regular V4's (so probably the b's too) there are canister caps scattered around the layout. Make a note where they are grounded. One of the canisters on the far side of the power amp runs a lead all the way back to one of the stars near the PT.

I've done some successful mods like adjustable bias, recaps and replacing the biscuit tone module and still have the pics. Send me a PM with your email address if you would like them. sh

PS Great amps. Beastly to lug around but they are grand. They also seem to have found a price point well above where they were a few years ago. I don't know if there is much upside but at least they won't be forgotten soon. Go here for more:

http://www.ampegv4.com/

[M Fowler]

Ampeg V4b

Got a text for amp repair at 3:30am I was awake anyway so replied back, I bet they shit when I did that.

Brought it over today and said an amp repair business in Minneapolis did a famous mod to it (unknown what mod is) and said well you will have problems with amp shutting off with this mod but it will be okay?

Amp now won't turn on per customer.

I'll dig in and figure it out I hope.

[M Fowler]

External 6A fuse was okay.

Internal 10A fuse was blown not sure why. In series pigtail fuse holder which is shown by the schematic glued to the amp panel.

But why can't I relabel the external fuse holder to 15A and use a single fuse rather then series fuse of 16A?

[martin manning]

Fuses in series will open the curcuit at the lowest rated amperage, so to be safe you would just jumper the 10A. I think this kind of scheme is designed to let the owner replace the external fuse, but if the higher-rated internal fuse goes (meaning something is really wrong, as opposed to the fuse opening due to some random event) putting a larger fuse in won't work, and he will be likely take it to a tech.

[JazzGuitarGimp]

Mark, think of series fuses as a length of chain: as you put tention on the chain, the weakest link will give way first. Amp manufacturers use this fusing approach to protect the user from his own ignorance: the 6a fuse blows, maybe the first time, the user replacese it with a 6a fuse. But if that one blows, "wisdom" might suggest wrapping the blown fuse with tin foil, or just popping a nail in the fuse holder. If there is something seriously wrong with the amp, the weaker link (this time, the internal 10a fuse) gives up, quite possibly preventing a fire - and causing the user to take the amp in to a qualified tech to diagnose and repair.

[M Fowler]

Thanks guys will keep as is and have tech look into reason for internal 10a fuse blowing.

[Leo_Gnardo]

Thanks guys will keep as is and have tech look into reason for internal 10a fuse blowing.

Maybe one of those "super smart" guys stuck in a really big fuse, or tinfoil or nail as mentioned, popped the internal fuse, then after polishing their halo, stuck a proper 6A fuse back in. "Can't imagine what happened." I can.

There's no particular reason besides trying to outfox the wily overfuser, to have series fuses. You certainly can do without 'em. Lots of amps have just one line fuse and that's all.

[cbass]

Thanks guys will keep as is and have tech look into reason for internal 10a fuse blowing.

Hey I know a really good amp guy in mn

[M Fowler]

Thanks guys will keep as is and have tech look into reason for internal 10a fuse blowing.

Hey I know a really good amp guy in mn

Yeah Jana but she is way too busy.