Alamo Capri 2560

[Mozart1220]

Hello! I am new to this board. I picked up this amp for free at a garage sale. It works but has an incredible hum. I know NOTHING about electronics, but I like old amps. I was just wondering if it's worth fixing up. I am also, for the time being at least, a boy on a budget. Are they expensive to fix?

[Jazz P Bass]

Welcome to the Forum.

The Alamo Capri 2560 is basically a table radio circuit (without the 'radio' part)

So it is not going to be a loud amp.

If you are o/k with that, keep in mind it is old.
At the very least the elecrolytic capacitors will probably need replacing.
And the speaker may be dry rotted.

Here is a schematic.

[Justin Thomas]

Cool, an amp with an iso tranny, but with line-voltage tubes! That fact alone makes it worth fixing up to me... caps and a cable are pretty cheap. Most amps with that compliment are widow-makers. But how about a grounded power cable?

Maybe $30 in parts and some of your time? Tubes should be fairly cheap, id needed. And it won't sound like anything else...Yay!

Justin

[olddawg]

Someone may correct me. But if you put a chassis grounded cord on this amp the way that series filament string is laid out with a chassis ground, you will have problems. I would consider floating that filament string. If you just want to hear what it sounds like, replacing the two 40uf B+ filter caps might get rid of the hum for the most part. If you know NOTHING at all about electronics and have NO experience, even a small amp like this can be deadly. Do your homework before you start poking around.

[Enzo]

No, the heater string is just three parts in series across a transformer winding. That one side is ground is about like having one side of the B+ being ground. Those high voltage heaters are not connected to the mains wiring, and that is where the danger lies in a widow maker.

[olddawg]

No, the heater string is just three parts in series across a transformer winding. That one side is ground is about like having one side of the B+ being ground. Those high voltage heaters are not connected to the mains wiring, and that is where the danger lies in a widow maker.

Ok Enzo. I was just thinking if he earth grounded the chassis with a 3 prong cord, and one end of the filament string is grounded to the chassis, even though there is an isolation transformer, it could put 100v AC from the filament string to the common ground point.

[Mozart1220]

I appreciate all the replies, but if I'm to fix this amp up, I'm going to have to pay to have it done. Like I said, beyond plugging stuff into the wall I know nothing about the technical end. I DO know about getting zapped by different polarities between the amp and PA system. I will have to look into restoring the old boy.

[g1]

Olddawg, some of the older Fenders grounded one side of the heater winding, no problem adding 3 prong cords to those. Same deal here.

[olddawg]

Olddawg, some of the older Fenders grounded one side of the heater winding, no problem adding 3 prong cords to those. Same deal here.

Yes I understand that. But that was a 6.3vac, not a 100 vac series string like this. Truthfully.. The schematic is a bit blurry on my phone. Earthing the chassis just didn't seem right with a modern ground schem.

[Enzo]

OD, you are looking at it backwards. yes, one end of the 100v filament string is tied to ground, but it is the OTHER end of the string with 100v on it. This is absolutely no different from the B+ circuit sharing the same winding (though a higher tap) and having one end tied to ground.

Ground is ground, the ultimate reference point. Any circuit you tie to it will refer itself to that level, it won't be pulling the ground all around to other voltages. Imagine if we had 6.3vAC tied to ground, and 300vDC tied there and -60v bias supply tied there. Ground won't be yanked up to some combination of the three.

Yes it will be successfully argued that the tiny resistance through the chassis ground and any ground wires will result in a small voltage drop - the source of ground loops - but that is never going to be more than a tiny voltage, and it will threaten only your nice quiet hum free condition, not your heart beat.

[olddawg]

OD, you are looking at it backwards. yes, one end of the 100v filament string is tied to ground, but it is the OTHER end of the string with 100v on it. This is absolutely no different from the B+ circuit sharing the same winding (though a higher tap) and having one end tied to ground.

Ground is ground, the ultimate reference point. Any circuit you tie to it will refer itself to that level, it won't be pulling the ground all around to other voltages. Imagine if we had 6.3vAC tied to ground, and 300vDC tied there and -60v bias supply tied there. Ground won't be yanked up to some combination of the three.

Yes it will be successfully argued that the tiny resistance through the chassis ground and any ground wires will result in a small voltage drop - the source of ground loops - but that is never going to be more than a tiny voltage, and it will threaten only your nice quiet hum free condition, not your heart beat.

As usual, I stand corrected Enzo. Just wasn't sure. And.. I did say I probably would be correct.

[olddawg]

I appreciate all the replies, but if I'm to fix this amp up, I'm going to have to pay to have it done. Like I said, beyond plugging stuff into the wall I know nothing about the technical end. I DO know about getting zapped by different polarities between the amp and PA system. I will have to look into restoring the old boy.

Honestly, before investing in it I would suggest you look on EBay, etc to see what working units are selling for. If it cost more to fix than it is worth, you might be better off and more satisfied buying a used Epiphone VJ, 5watt Blackheart, or any of the small amps that have been available the last 10 years for $89 from a kid on Craig's list.

[Mozart1220]

Honestly, before investing in it I would suggest you look on EBay, etc to see what working units are selling for. If it cost more to fix than it is worth, you might be better off and more satisfied buying a used Epiphone VJ, 5watt Blackheart, or any of the small amps that have been available the last 10 years for $89 from a kid on Craig's list.

Well, I have a good Peavey combo for gigging, I just found this in a "free pile" at a garage sale and figured what do I have to lose? I also have a little "Kustom" practice amp that's got more beef than it seems like it should.

[Enzo]

Like anything else, your priority is to wind up with an economical amp to play or it is to have a fun project to spend some time on. Usually the projects do not satisfy both of those priorities.