Just picked up an Adcom GFA-5800 (broken)

mmadden28

I just need to get more sleep

disneyjoe7

ben62670 wrote: »

Yes Mega he scares me. He brings back memories of polarized caps being inserted backwards in my first amp project. Lots of stinky explosions!

I did that just to see what it does.... Well there's wasn't much left of the cap :eek:

ben62670

I dove under the table like there was a drive by and unplugged the amp. It was all over except the pungent smell of the exploded caps.

megasat16

I looked at the schema of this amp and there are one AC main fuse (15A) and two voltage gain amplifier fuse of 0.5A each for driver stage.

There are also two output protection fuse of 10A each for overloading protection (short circuit).

There is no DC protection circuitry as with many other NP amps. This is one of the as simple as it gets amp.

megasat16

mmadden28 wrote: »

When using a light bulb for an amp, what wattage/resistance bulb is best
I'll have to get my list

I think to use 100W for starter just to be safe when trying to test it out and measures a few critical voltage at different components.

But this amp consumes 250W idle so I think the light bulb is not gonna get dim even when the caps are charged. You'll need to use 300W to even witness the lightbulb dims a bit when the caps are fully charged and the amp is working normally.

mmadden28

mmadden28 wrote: »

On another note, I built a series in-line Light bulb outlet.
...

I stood in Home Depot for a little while trying to figure out the best and easiest way to do this, with no exposed wiring, and nothing involving mounting anything in a project box, etc.

Pretty darn simple--The two receptables are split and wired in series, with the light bulb adapter (and light bulb) completing the Neutral part of the circuit in the top receptacle.
With the bulb in place I have 120V at the bottom outlet. No bulb, no voltage. Optionally I could just plug any standard lamp into the top receptacle instead of the bulb adapter thingey.

The completed project:



The wiring:



The next phase might be to put this into a project box or dbl gang box, and include a shorting switch and an ammeter.

mmadden28

OK, so on a Variac---if price is essentially the same:
New 5A (made in China)
or
Used 10A (Made in the US, STACO)
??

Is this one of those things where they don't make em like they used to?

Are the new China builds decent?

Will I ever need 10A, or will 5A do for most purposes? I'm guessing that if you get up above that you might as well run full power without the Variac right?

disneyjoe7

Call me old school but while I was learning electronics, we only had a 5 amp VARIAC around, but that was like 25+ years ago. If I remember correctly it didn't even have a voltage meter on it, which I find idiot thing today if you can't figure dail above. A meter should be current if anything not voltage just me I know since they all come that way. Remember you're testing not playing the unit so 5 amps is more then enough. Just my $.02

disneyjoe7

mmadden28 wrote: »

I stood in Home Depot for a little while trying to figure out the best and easiest way to do this, with no exposed wiring, and nothing involving mounting anything in a project box, etc.

Pretty darn simple--The two receptables are split and wired in series, with the light bulb adapter (and light bulb) completing the Neutral part of the circuit in the top receptacle.
With the bulb in place I have 120V at the bottom outlet. No bulb, no voltage. Optionally I could just plug any standard lamp into the top receptacle instead of the bulb adapter thingey.

The completed project:



The wiring:



The next phase might be to put this into a project box or dbl gang box, and include a shorting switch and an ammeter.

Now find yourself a 3 way lamp around with say 50/100/150 or a 40/80/120 bulb and start with the low setting. You can always turn up the current by turning the lamp to a higher setting. I played with stuff, but was a kid with no cash most of the time.

mmadden28

disneyjoe7 wrote: »

Now find yourself a 3 way lamp around with say 50/100/150 or a 40/80/120 bulb and start with the low setting. You can always turn up the current by turning the lamp to a higher setting. I played with stuff, but was a kid with no cash most of the time.

I didn't have a 3 way lamp hanging around so I bought a 100, a 200, and a 300 watt clear bulb

mmadden28

disneyjoe7 wrote: »

Call me old school but while I was learning electronics, we only had a 5 amp VARIAC around, but that was like 25+ years ago. If I remember correctly it didn't even have a voltage meter on it, which I find idiot thing today if you can't figure dail above. A meter should be current if anything not voltage just me I know since they all come that way. Remember you're testing not playing the unit so 5 amps is more then enough. Just my $.02

How about this thing--it ought to take care of any Variac need I can possibly imagine :eek::eek:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110448390655&ssPageName=STRK:MEWAX:IT

Its only $100 (plus freight)

disneyjoe7

No it looked like that $50 one you're looking at. If you did the light bulb thing, I would start with a smaller watt bulb.

megasat16

Good job on making the light bulb thingy! Looks neat and safe to me!

Staco Variac is a good one but it's old. Don't know it'll work correctly or you need to replace carbon brush, etc.

Buying new will ensure it'll work out of the box mostly.

mmadden28

I might have to take my chances with Newark and hope to get matched parts, I got no responses except from the Adcom recommended place, and only after I emailed them again, I sent a detailed list of what I need and asked if they can provide and if so to let me kow how much. This is all that was in thier email:

we have parts partualy
not all in stock

That's it.

You'd think that in these times businesses would do a little more to help promote a sale. WTF?!! Frustrating!