Hi nice bgw i have had many bgws in the 80s we use to install them in clubs i am a electronics tech for 40 years repaired a lot of audio and video watch a lot of your videos very interesting keep it up and keep safe Thank you
That old fan sounds like the bearings are a bit dry hence the jet engine sound (took ages to spool up to speed and dropped off like a stone when the power was cut) like you say though probably end up with a modern fan that was quieter out the box.
That is an impressive unit of power. I never saw one and noticed the 21000 microfarad caps on the power supply. Serious filters and a wall of TO-220's. Nice job!
@@renderingrocks Do you know what a class C amplifier is? No you don't or you wouldn't asked that question. Class C is a RF amplifier only, for fixed frequency work. It only amplifies less than half a waveform, and the remaining portion of the waveform is reconstructed by the tank circuit. Think FM transmitters. Never ever used in an audio circuit. This is class B, push pull, biased as class AB. An ancient bulletproof design designed for stupid power levels and efficiencies. There were many much cleaner amps that followed by companies like Sony and Technics that used a sliding bias (Lagato Linear for Sony and New Class A for Technics) which by sliding the bias up under lower power levels drove down the efficiency, and reduced distortion to almost un-measurable levels, this one however is not in that class. It is a fixed bias amp with reasonable distortion levels for it's design, and insane power levels for the time.
At first I was surprised that's a 20W resistor for a little fan. Since P = i² * R, the current through the fan at low speed is potenially 250 mA max. Not too far off (I think) compared to a computer fan. Still not efficient, but I guess less parts and the fan power is negligible compared to what the amp draws.
That fan is knackered! There's no soft-start that I saw and it took a loooong time to spool up to full speed. Great video. Impressed at how quickly you narrowed in on the problem. I'd recommend that the customer gets the fan changed out though. I wonder if that fan is partially seized, and hence pulls more current through the 300R 20W resistor than was originally intended, and hence took the resistor out?
It's not seized. Turns completely freely. Those old resistors fail when the cement that they pack them in cracks and lets moisture and oxygen get at the steel wire that is wound around the core. Heat, moisture and oxygen makes the wire rust and it eventually breaks. It's actually quite common here in the salt air we have living on the coast.
That fan motor seems like it takes a l-o-o-ng time to spin up to full speed. I wonder if there is something wrong with it... oh well, he'll probably want to replace this one with a computer fan, too.
Wouldn't a new, quieter fan be a good idea to install? Some of the latest fans are almost silent, even at high speeds. Tnx for the video, always enjoyable.
What a beast!, it sounds like a hovver craft :-D I suppose if it was yours, you would use 2 parallel 20 watt ones at 620 ohms each, that would stop it's game.
Sound like turbo fan airplane engine ready for for lift off. Kind of primitive way of controlling the fan - I bet the amps were made during '80s. +/-80V on rails - that's some serious voltage swing, somewhere in 0.5kW at 8ohm. If something blows - I don't want to even think about repairing it, as finding replacement parts for it won't be easy.
@12voltvids, when temp sensor is shorted, why does the fan seem to "slowly" ramp up speed over several seconds instead of within a second or two? Is that ramp-up built into the fan itself?
@@12voltvids Huge filter caps probably. When I did live sound, not uncommon to have 2 3-way amplifiers racks totaling 5000 watts +. Remember one gig where not enough power and lights dimmed every time bass drum kicked. lol The Crown Macrotech 5000vz was known to bite at techs. The Crown Macrotech 3600 had a 30A 120v plug.
@@leeselectronicwidgets they are not that close. They won't fall off. The thermal switches are about 1/2" thick so plenty of clearance. They are under the cover so nothing is going to come in contact with them.
Looks like Tim the tool man Taylor tried to give it more power! Lol 😆. But seriously, leaving it on all night was probably the cause of the fan having some dust/lent, and then quit blowing air !
@@b.powell622 No thats how they sound. I have an old scope with one of those noisy fans on it, and they make a real racket. Draw lots of power too, about 200 watts on full power as they move a ton of air.
@@12voltvids ok, wasn't sure about that. I have a soundcraftsmen power amp, 800 watts per channel, and the fan doesn't get that loud, but moves a lot of air. Thanks again for your video. BTW, I would like to install a soft start circuit in this amp. When I turn it on, you can hear the current industry and the led array pegs out momentarily, if you could recommend a circuit diagram, I would be very grateful! Thanks again, God bless 🙏
@@b.powell622 That sounds like the amp is becoming unstable at startup and putting out DC for a split second. My friend was having a backyard party with a big Randall pro amp and all the speakers shot out the voice coils and stuck there when he powered it up. That would put out 900 watts per channel into 2 ohm load.
@@12voltvids That inrush current is killer, must have some soup can sized power caps in there, guessing 75 watts at idle? Hook it up to a kill-a-watt meter? Got me curious now..
i never seen a BGW Power Amplifer beofre? I seen fans be loud On My Build Gaming PC i have 3 fans on the front one over the board and the back mounted power supply has a fan on thre back
Bgw were custom built for movie theatres for the movie earthquake which was the first sensourround movie. Most of the ones circulating around were removed from theatres after the movie finished it's run. Made in California i believe. Theatres weren't the only use, they were used mostly in professional applications. Bars, disco, night clubs ect.
