Monster load banks

[olddawg]

Back in the day I had a load bank that would cook a thousand watts at 4 ohms. I don't anymore. I have someone bringing me some rather large rack amps that are dropping a channel after half an hour or so under use. I no longer have a monster load bank. Any tricks?

[Enzo]

I have enough loads here, but some guys have suggested a burner for an electric range - a kitchen stove. That will handle all th watts you got, and is cheap at HomeDepot or similar.

And first thing I would do after cleaning them out, would be to sit them there unloaded and no signal and see if any get overly warm. And then I would set the bias on each channel, regardless of how well it sounds or seems to work. Overbiased channels can thermal out.

Are these rack amps living in racks? And will you receive them that way? or will they be pulling them from their racks and handing them over? I am concerned for cooling air flow. Amps require fresh air for cooling, and they can be racked up in a box that doesn't breathe. I had a customer one complain his Yamaha amps were overheating. Especially since he even added a cooling fan panel in his rack. But what he had done was ignore that the amps drew in cool air from the front and blew it out the rear. And he had made a rack panel with three fans across it, and they too blew air into the rack. The net result was all those fans just pressurized the rack, but allowed no airflow THROUGH it. All he needed to do was turn hos three new fans around, and all was cool. Pun intended.

So consider the environment the amps operate in, it is as important as the amps themselves.

[diydidi]

Apparently the 110V smoke machine elements measure almost exactly 8 ohms. They can do a kw or more. Haven't tried them myself, but spoke to a tech buddy of mine in Cape Town, South Africa, and he says he uses them without any cooling mounted on a base plate on the wall, and they are awesome.
Now to find out where to buy them loose...

[Leo_Gnardo]

IIRC water heater elements another cheap & easy to find load R substitute.

+1 to Enzo's comments about rack cooling. Local club with national acts on the stage, had a rack of Crown DC300's. Naturally they kept thermalling, and I told them the cheap & easy fix was a $15 window fan from K-Mart. No, they couldn't do that, they're sooo smart, and cheap, they got a $5 clip on fan instead. Which of course did nothing to alleviate the problem. Then they sprung for a rack full of Taiwan-made Yamahas which gave them endless failures. From the frying pan into the fire... duh! all the way.

Another bugaboo in self-fanned amps: they tend to load up with dust & hair. One of my customers scored the house PA amp from the fabled Maxwell's in Hoboken, a well used BGW 750 crammed to the limit with dust 'n debris. One more molecule of dirt & I think the 750 would have exploded. A good vacuuming-out and a squirt of Caig D-5 to the volume pots had it running like new.

https://en.wikipedia.org/wiki/Maxwell's

Geeze, what a history of music passed thru that amp!

Hope you have a good shop-vac olddawg, might be needing it.

[tedmich]

Mike Setzer described hooking a bridged QSC 1500w amp to a std electrical outlet and then plugging a 1200-1500w toaster oven into it. He reported the oven measured 8 ohms cold and rose to 12 ohms when it heated up. He also used a 1685w hotplate at ~10 ohms.

see:
Re: using stove element for dummy load? - AMPAGE Archive

[olddawg]

I understand all this. I was a Yamaha Authorized Tech for over 20 years. I just don't have the equipment at home I did in the shop back in the day. I have a pretty well equiped bench, just no big load bank. Yes I will check the obvious. But if it is failing under load and only one channel of a stereo amp, oh well.

[olddawg]

I have a hot plate. Time to measure the resistance.

[g1]

If you have an electric kettle, measure that too.

[Drewline]

We used a pair of steam irons.

[Enzo]

And for that matter, nothing says both channels of an amp have to be either in or out of bias.

[bob p]

Mike Setzer described hooking a bridged QSC 1500w amp to a std electrical outlet and then plugging a 1200-1500w toaster oven into it. He reported the oven measured 8 ohms cold and rose to 12 ohms when it heated up. He also used a 1685w hotplate at ~10 ohms.

see:
Re: using stove element for dummy load? - AMPAGE Archive

I thought I'd click on the old Ampage link to review what had been said on this subject... I know a bragadocious fellow who "upgrades" old Carver rail-switching amps, gives them outlandish specs, and then guarantees them for life. I had the idea (I thought it was novel when I thought of it) to challenge him to a "Let's cook breakfast" death match, using resistive loads to make breakfast. Just as you might expect, my new idea wasn't so new ... Mike Setzer described doing exactly the same thing back in 2003. What amazed me most is that my name was on the top of that thread that @tedmitch linked to. I was totally surprised to see that I was participating in that thread back in 2003. Here I am thinking that I had a novel idea about making breakfast ... I guess my memory isn't what it used to be.

Regarding suitable loads -- I'm not doing anything fancy. I just use vitreous enamel resistors placed in a suitable cage, and nuke them until they glow. Seriously, in a proper cage you can overdrive them until they glow orange. Just be careful you don't start a fire. A good metal screen cage is a must to prevent a fire or an accidental burn injury. My cage is mounted on a concrete wall with a $15 K-Mart fan blowing on it.

See Leo? Great minds think alike.