OP
- Thread Starter
- #61
That was one dirty PC and he's for sure gettin it clean.
I will even be Corona virus free now.
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Amp Dummy Load
- Thread starter Sal1950
- Start date
I will even be Corona virus free now.
You don't need any load to set bias. In fact most of the Adcom service manuals suggest doing it with no load. You can't test offset with a speaker attached.
When I do need a dummy load I use an 8 ohm 10 watt or 25 watt resistor and submerge it in a coffee mug of water. This works great.
When I do need a dummy load I use an 8 ohm 10 watt or 25 watt resistor and submerge it in a coffee mug of water. This works great.
OP
- Thread Starter
- #63
GFA-545 II service manual.
Demineralized water would be important for ensuring a clean circuit, but water on electronic components is usually a bad idea. Water corrodes metal and gets into small places, where air does not dry it well.
Isopropyl alcohol is a good idea for cleaning circuit boards and leads/terminals. Aluminum has about 400 times better thermal conductivity than water, so metal works for dissipating heat from dummy loads.
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It's what i did a few years ago. Went to the 3 local Lowes with my ohmmeter, and cherry picked a well stocked 16ohm, 3500W, water heater element.
Got eight of them, all +/- 0.1 ohm. So it's of course easy to make any common load of 2, 4, 8, or 16 ohm.
At the time they went for $7 a piece. 28kW load for under $100
The great news in testing, was that their resistance didn't change significantly under load / heating up.
Distilled water will dry fine even in crevices if the part is warmed with a hair dryer. Old IBM service guys I know routinely used it for mainframe computer PCBs that were bathed in cigarette smoke back a few decades.
And dummy loads for ham radio often submerge a 50-ohm power resistor in a paint can filled with transformer oil. My “Cantenna” was one such. Using an 8-ohm power resistor would work, too. These were rated at a kilowatt.
The water-heater elements are a brilliant idea.
But my main reason for posting was to offer this thread as an example of good humor and good information coexisting and not lapsing into endless arguments.
Sal, are you still using those Adcom amps? I still have a 535 in service.
Rick “an earlier time in ASR history” Denney
And dummy loads for ham radio often submerge a 50-ohm power resistor in a paint can filled with transformer oil. My “Cantenna” was one such. Using an 8-ohm power resistor would work, too. These were rated at a kilowatt.
The water-heater elements are a brilliant idea.
But my main reason for posting was to offer this thread as an example of good humor and good information coexisting and not lapsing into endless arguments.
Sal, are you still using those Adcom amps? I still have a 535 in service.
Rick “an earlier time in ASR history” Denney
You sent it out for service or are servicing it yourself? It appears to be a pretty simple layout and design...
You sent it out for service or are servicing it yourself? It appears to be a pretty simple layout and design...
By “in service” I mean “in use”. Far as I know, it has never been on the bench. I’m happy to service stuff myself if I can find manuals, but for some reason I end up with stuff that has unobtainable service information. The original 535 probably isn’t an example of that, but it works well and I haven’t been tempted to open it up.
Their GFP-565 is another thing—that one needs a visit to the bench.
Rick “would really like service manuals for some B&K components, a Naim CD-5, and the GFP-565” Denney
OP
- Thread Starter
- #69
Sure, 3 x 545 IIs and 2 x 535 IIs for my 5.2.4 multich rig. The 545s power the 5 base channels and the 535s the Atmos ceiling channels.
The only service mine have required is the biasing and offset checks I've done myself.
Wasn't that the one that got stuck with a bad run of cap's that failed all over the place?
The thermal conductivity of transformer oil is really bad like air. Air is an insulator, so that is why the dummy loads heat up instead of spreading the heat into the air more effectively.
It is better to place the dummy loads on aluminum and even steel than other materials that are generally available to individuals, so it makes sense to use the metal chassis, or for example cooking pots.
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The issue isn’t conductivity so much as thermal mass—a gallon of oil has a lot of it. But these are proven devices for short-term testing of thousand-watt RF transmitters, and they are not expensive.
But those water heater elements are rated at 4000 watts when submerged in water, though at that consumption they will make the water hot after a while (which is rather the point). But they are extremely durable in that application, especially for intermittent use.
Rick “who has dumped 600 watts into a Cantenna for minutes at a time” Denney
Yes, but that was just one batch and mine don’t seem to be suffering from that. But even if I replaced them, I’d want to perform the adjustments in the service manual again.
Rick “needs to do the same for the B&K preamp” Denney
The issue is conductivity due to how hard it is to know how hot the dummy loads actually are in oil or water, unless they are touched directly or have a thermometer connected directly to their chassis. This could lead to overheating or soakage problems that are not durable for dummy loads.
One ideally has at least as good conductivity as the chassis of the dummy load if overheating is even an issue. It is wise to oversize the wattage of the dummy loads if the price is rational. An extra heatsink might not be necessary, however the rated wattage of chassis mount resistors is vastly reduced without an extra heatsink from the ones I have read the spec sheet for.
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