I used to work on these death traps. Once I had a TO95 transistor blow into my forehead which left an impression for weeks, much to the amusement of my fellow technicians. As I'm sure you know, always be extra careful when working on such beasts as they don't give second chances. Loved and subbed the channel BTW!
I was 10 years old in 1974. I remember going to see Earthquake in "Sensurround" at the theaters and the seats did indeed shake. Little did I know that these were the amps used.
I worked in a big London West End Cinema when Earthquake was first shown. The film company sent a couple of engineers to install the Speaker and Amplifier. The sound was phenomenal. I often wondered if it would dislodge the old plaster ceilings when the films were shown.
I watched earthquake way back, the sound was amazing. The whole theater shook.i was told it's a separate audio track triggered off the movie sound. I loved it and sad it will never come back.
I worked for Automated Processes inc (API) in the 1970's. We made recording consoles for studios. We also made some amps for Sensoround used for Earthquake.
I have a bgw 500d, I call it the "arch welder" 😂 I made a buddies house power dim with every bass punch during a New year's party. The only repairs I've made were changing out the big resistors as they do get very hot and I've had one burn up, not now with 10watt flame proof one's 👍. Get amp for sub channels with the high distortion as it's not as noticable. I also just remembered I had a similar issue with the plug connector having slight oxidation from living in the West coast of BC. Terminal fretting. Cleaned terminals and installed dielectric grease, all good now. Good job 👌 keeping the brute going 😁
Brian Gary Walkner graduated from Alexander Hamilton High in maybe 1966-1968. My friend Jon Prudeaux who created his own company Crest Audio was one of the Engineers then. BGW was in Culver City California. They were the first company to use a Crow-Bar circuit to protect the Output Transistors. 100% Hand built and soldered Amplifiers.
bgw TRIED TO GET USERS TO REALIZE THAT Crown DC-300 would max out & clip into efficient JBL speakers and burmn out the voice coil .... the trick was to run the amps at SOA safe operating area and NOT to clip them ..effectivlly causing 'DC' across the voice coil.. I sold many of BGWs amps in Illinois & Wisconson back in the 80s . Also the DC300 would blow a final and send the rails to the voice coil ...PUFF causing an out of warranty on the speakers ( JBL ) Our firm represented both JBL & BGW....back when JBL used indepentent sales rep companies...." good ole days"
Nice to know! Thanks for that. Crest certainly took things to another level ...ie., robust, BIG power, high damping factor. Peavey bought Crest if I'm not mistaken.
"Earthquake"... Those were the days. I saw the movie in the theater when I was 15 years old. It was a thrill (pun intented). The story was second to none, it was all about the sensurround effect. I remember the great Charlton Heston, aka the mythical 'Ben Hur, playing the role of Stewart Graff, a construction worker in "Earthquake".
I purchased a Universal 8 condensed 20 minute super 8 sound version of that film way back in the early 80’s from a company called Famous Films in Florida. I used to hook my projector speaker out to a cheap solid state guitar amp and crank it to get the rumble effect. And of course I’ve seen the movie in it entirety. Cool movie.
Good way to effortlessly fry tweeter voice coils (whoops...) It's also easy to short component leads to the heatsink. I pre-cut all the leads through a perfboard when working on these to keep that from happening. It should be able to do 800W into 8 ohms in bridge configuration just before clipping...good for quickly heating a room and overheating the standard 16AWG AC line cord! Time to hook it up again since winter is almost here. I still can't get over the absolutely mental size of the power transformer and filter caps in these things...back when the purchase price got you a healthy portion of gravitational pull.
Great job. Though it might also be a good idea to also touchup the solders on the socket for the wiring harness. Might have missed you giving it a good look over and determining it was OK. Nice to see the boards didn't show signs of overheating - must be well engineered.
The 750 G was the last of those big amps. It had a large led display for output power and thermal light for power supply and heat sink and dc offset lights as well.
Not sure how I missed this vid but found it now. These amps are awesome for how simple they are, there's a few similar (but obv. silicon) builds floating around YT where they simply point-point the whole thing together with no PCB or cabinet & I keep meaning to make one one day! At 130dB who's worried about THD numbers anyway, chances are what you're listening to wasn't produced enough to matter. Almost enough to drown out the wails of audiophools :D
Why did you not hook it up to your function generator and scope? Not related to this video with its TO-3s, how do you quickly check TO82 BJTs in circuit to make sure that they are probably good?
""Sensurround"" was this amplifier driving a Cerwin-Vega 18 inch subwoofer model 189 ES they were in a horn loaded cabinet, the type of horn depended on the theater they were installed in. The number of amps and subs depended on size of theater.
i came across a 1970's cerwin vega amp it was being tossed i grabbed it i restored it and most of the output transistors where shorted, came out of a club if i recall
A big old beast, a brute as you said :-D Oddly i thought there was a semi short through a mica insulator so the heatsink had power, the heatsink is earthed to the case so it could have leaked. I've had trouble with mica insulators and a tiny spec of solder :-(
Got several BGWs, my dad had a 1000, their first if I’m not mistaken. I have a 750g from 89’ that just started flashing idle lights on power up I can’t seem to fix. Need someone with some expertise.
I noticed a couple of suspicious 'rings' in the solder connections of the upper row of power transistors (22:35). Probably bad connection due to heat stress. That solder may have been reconnected when you unsoldered/soldered the emittor resistors prior to testing the transistors. Better reflow them all.
I managed to collect three of the 500d models over the years. I think they are nicer looking than the 750s, having the brushed aluminum face plates. Supposedly they have less power than the 750s but the schematics for them as far as I could remember were essentially the same. I never knew why they were rated having a little less power.
That amplifier looks so cool ! Vintage electronics is the best, since the qaulity was on whole another level compared to " consumamble electronics" nowadays. Things were built to last nuclear war back then.
Just FYI the LM 318h op amp is all over ebay for about $5-10. They like to take out a positive and a negative output when a channel goes. Will trip relay out if one gets leaky too.
I had the same problem 10 years ago, when you listen to quiet music it works perfectly when you turn the volume up under load and heat builds up, some of the end transistors defected and stuck closed and stay closed until the amp is energised and hot. That defect is extremely hard to find ... it took me half week to catch it and test transistors under load separate from the amp to see which one sticks.
While the outlets are 15 amps / 1800w it's worth noting that continuous loads can only draw 12 amps RMS. Alec from Technology Connections did a video about Space Heater Nonsense. The short version is they're virtually all rated 1500 watts.
The maximum amount of power you can draw? 𝟭𝟬𝟬𝗮𝗺𝗽𝘀 for a couple seconds. To avoid nuisance tripping, a breaker will pass extra-ordinary amounts of current for surprisingly long periods of time. A 20 amp circuit can pass 7-8 times the rated 20amp trip amount, ... for up to a second or more. It will allow up to 3x the rated amount for up to 10sec or so. It can allow up to 1.5x, to 2x the rated amount for a period extending as long as 30 seconds! Thats; 𝟭𝟬𝟬𝗮𝗺𝗽𝘀 𝗳𝗼𝗿 𝗮𝗿𝗼𝘂𝗻𝗱 𝟭-𝟮 𝘀𝗲𝗰𝗼𝗻𝗱𝘀, 𝗮𝗯𝗼𝘂𝘁 𝟲𝟬𝗮𝗺𝗽𝘀 𝗳𝗼𝗿 𝗮𝗿𝗼𝘂𝗻𝗱 𝟭𝟬 𝘀𝗲𝗰𝗼𝗻𝗱𝘀, 𝗮𝗻𝗱 𝘁𝗵𝗲 𝗰𝗶𝗿𝗰𝘂𝗶𝘁 𝘄𝗶𝗹𝗹 𝗮𝗹𝗹𝗼𝘄 𝟯𝟬-𝟰𝟬𝗮𝗺𝗽𝘀 𝗳𝗼𝗿 𝗮𝘀 𝗹𝗼𝗻𝗴 𝗮𝘀 𝟯𝟬 𝘀𝗲𝗰𝗼𝗻𝗱𝘀! All from a 20 circuit!
No, any protection circuit would reset as soon as power removed. These type of Amps don't have any logic. They monitor for any DC voltage on output and if any detected it opens the speaker relay. Once the voltage goes away the relay closes.
Might be a good idea to advise the customer against hot-swapping cables or connectors on an absolute brute of an amplifier like this! It's asking for trouble! ⚡
Didn't take my content. Took musicbakery royalty Free music and slowed it down and claimed it was theirs. I used that track on a road trip video and got a claim. I disputed it as usual as I have a license to use it.
That what they were used for in the movie theatres. Subs where distortion won't be noticed. Actually in any high power application because the ear doesn't detect distortion as easily at high volumes anyway.
Lucky again. Maybe cold solder, maybe oxydation on the plug/socket connection. I hate when the output section blows - it can take with it drivers, predrivers, VAS, voltage bias section 🥴🤬. This one has current limiter, so it would be hard to blow the OS. But try to get parts for some of the older gear, yeah. Now in the same chassis you can find 5kW of class D, but they're almost unfixable. I heard the N Cores from Hypex, very clean, high resolution amp. And my other friend picked up 2ch Pascals boards to try - integrated PS, bla, bla, but everything SMD.
Yup class D are certainly powerful and efficient. I still prefer the sound from my 40 watt vacuum tube amp. Mind you a tube amp requires very good efficient speakers and these days getting good efficient speakers cost an arm and leg.
I'm surprised you didn't clean up the plug and sockets. I suppose the act of unplugging and plugging them in again would clean up the contacts a bit but why not clean them while you are there especially if you suspected a bad contact? I'm not having a go at you it's just an observation and would love to hear your thoughts on that repair. Keep up the good work.
@@12voltvids Agreed but a little deoxit a brush and multiple insertions would have helped. Again, I'm not having a go, it's just a thought. I totally respect your work and I bow to your knowledge of older equipment. It's hard to get my true thoughts across in such short conversations without sounding abrupt, I promise you that is not my intention. Peace.
You can still buy the LM318 in that TO-5 metal can style. Future reference' 1 Balance Compensation-1 2/3 Inputs 4 -V 5 Balance Compensation-3 6 Output 7 +V 8 Compensation-2
I don't think everyone will think of that, even if they could clearly see in the video, they'd still have issues? as the pin-out is in a circular orientation. Also if they had a burnt board etc.. having the text with the pin-out would help would it not?
@@12voltvids 1985 vs 1997 tech.... the guy that started crest, worked as a tech for BGW in the begining...lots of power you have.... sound similar to carver PM900 pro.....that has woofer killing powers!! i think is 450 into 8 ohms x 2 channel like yours...i owned a bunch of crest amps back in the day
@@lunam7249 260x2 into 8, 450 x 2 into 4. 1100 into 2 bridges mono. You are right the guy that started crest was an engineer with bgw on 70s. Crest was merged into Peavey. Yes it sounds simply amazing and will drive any speakers you can throw at it. It is pretty much unclipable as it has an electronic attenuator that will compress the input for peaks that would normally clip protecting speakers at that extreme power. I have killed a few speaker fuses by accident.
Wow, Dave...I knew you were good but now you've entered the realm of "Magic". Just looking at a piece and laying hands on it is enough for the cure!! Hallelujah. And Thanks... BTW, it's: .1% THD for 225 watts per channel, 20 to 20,000 hz, both channels driven at full volume, with 2 volts input. Guaranteed no more than... Anything less, the distortion falls to very competitive numbers. In the .02 and less range. And...anyway, I doubt I'll ever make it sweat that much. You should hear it drive a pair of Magnepans, a notoriously difficult speaker for an amp to control. Enough, I'm beginning to sound like I'm defending my girlfriend. Thanks for saving her, Dave
@@12voltvids Then why are people always warning you not to shock yourself on capacitors of unplugged equipment? You really do have a way of being an unhelpful smartass.
Any properly designed equipment will have resistors across the caps to discharge them when power is removed. Tube gear is different. They use high voltage and the caps can hold a charge so you need to discharge with a resistor or throw a screwdriver across and draw sparks.
With the lights on, they draw about 650 watts for the studio lights and the inrush from firing this brute up no wonder the breaker tripped. I have 2 circuits in the garage. Lights and garage opener on 1 and bench on the other. Plus 2 240 plugs for my car charger and heat. Draw lots of amps in here.
That's assuming 100% efficiency and perfect power factor. In reality around 75% amp efficiency and 0.75 PF is reasonable, so it's more like 12 amps draw. Definitely overkill for a home theater.
@@eDoc2020 Overkill is certainly relative. However, for subwoofer duty, and to adequately track the big pulses of low freqs that accompany the deepest effects, not overkill at all. Actually, it's likely inadequate. To maintain the same dB level, a subwoofer driver requires a 4x increase in excursion for every octave downward. That multiplies quite quickly. Plus, our hearing requires significant additional dB levels as the freqs extend lower. For 90dB@40hz, we require 18dB more to hear the same relative loudness @20hz. 18dB = 64x increase in power! So, especially in the home theater, subwoofer realm, it's not overkill.
The worst failures are when replacing output transistors and have missed to find out a burned kilohm resistor somewhere in the driving circuit or a leakage small transistor or a burned pcb trace that is not visible and when test it blows again with flash light in the fuses along with the short circuit sound.And have lost money with a couple of hours and then start again from zero.Freaking experiences.
That's why it's a good idea to use a series lightbulb when working on power electronics. It won't protect everything but it should help save the big expensive parts.
At least it's a Fluke so it should shut down before it malfunctions. Cheap DMMs like I have read high as the batteries go. I don't know how long it took me struggling with a 5v supply that was reading 8v. I even replaced the TL431 because it wasn't conducting even though the input appeared to be well over 2.5v. After that I've been more careful.
@@eDoc2020 It will be a fluke if it is accurate when the battery gets too low, and no it doesn't shut down but the display starts to fade and then the readings go out.
@@12voltvids sometimes Those Old 70's Amps & Receivers Aren't Worth Fixing. If The Parts Are Obsolete. I Remember I Had An Old 7p,s Yamaha Stereo Receiver The Power Supply Was Bad & I Called About A New one & It Cost More Then It Was Worth. So So I EOL'D it.
@@12voltvids I Found All Kinds Of Led TV Parts On Amazon. I Didn't Think They Had All Those Parts. Well At least I Know Where To Go To Get A Parts If I Need Them.
Dude...just remove that metal can opamp,fit a new dip8 socket and fit a new opamp,you could use: LM318,LF351n,NE5534 and god knows how many more lol,how to say that you can't fix it if the opamp is dead?!?! Come on man....i moddified my BGW a lot,change also the supply zenners for the opamp with lower voltage as the opamp on these amps ar powered to maximum +-20vcc and in case of a shock they will die,i reduced the opamp voltage in mine to +-5VCC and use a LF351N,no problems ever since,don't you ever say that you cannot fix something,there are thousands of ways to fix something,and these old designs are toys for me,i don't even need schematics for them,so be a pro,not a amature.
Op amp is fine. Not about to change something on spec. Perhaps you would and then change the customer only to have a pissed off customer when it breaks again. I hand back no change because it didn't fail. When it came back it the fault remained long enough to find the fault in the speaker protection circuit. This is why I have very loyal customers that constantly bring me stuff. Because i don't charge them 95 to do a "diagnostic' and even when it works find something to change to justify that charge only to have it break down because that guess didn't fix the intermittent. I only change parts after I can demonstrate the fault or if it is a catastrophic failure. Same as I don't shotgun cap replacements. That is a sure sign of an amateur that doesn't understand how they work and how they fail.
@@12voltvids You can always make them better,if you know the parts,you know the specs then is easy to make them unbreakabile,you should know that op is on is full rated voltage and that will kill him,changeing two zenner wont kill anyone and the opamp will say thank you,but your interest is to get damaged sooner or later...more money for you,i get the ideea,what about the customer?? they have no fking ideea what's inside of a amp or how it works so i really don't care about that,if they know better than me,i suggest them to fix them by themself,none of my amps that i fixed or moddified in the last 15 years failed,not even one of them,good parts ar indeed exepensive,but i respect myself and my work.
@@emilvladoiu91 they are operated at the designed voltage for a reason. Changing to a lower voltage for op amp will also change the charastics of the sound. Running a component at the max spec voltage will not shorten it's life. They have a designed operating voltage and that designed maximum operating voltage is still well below the voltage that will damage the component. Over current on the other hand will damage the device as current equals heat and heat damages parts but you already know this. There is a difference between max operational voltage and absolute maximum voltage. Many designs do operate close to the max operational voltage, right up to the limit. This is where the device is at its most efficient, signal to noise ratio of the highest, linearity at the highest. This is why they run them there. Changing the zener to a lower value because you think that will prolong the life of a part is nonsence. It lowers the dynamic range and the signal to noise ratio. Modders think they can outsmart the engineer that designed it. The engineer did the calculations. The exception is when the engineer makes a design change when a problem crops up and the factory issues a service bulletin.
Then can you explain why more then 80% of the bgw-s faults lays in the faulty op-amp's and blown outputs?? so in your opinion you should drive all the op amps and the semiconductors to maximum voltage....now i see why your amplifiers fails and mine doesn't. You speak about SNR on a power amp?!? I hope this was a joke....like someone will keep an almost 1kw amplifier as headphone amplifier to keep an eye on SNR ratio. My goal is to make an amplifier bulletproof,Crown Macrotech's have 100Db SNR,this one have 106Db,do you think that my low voltage op now will loose more than 6Db ??? i don't think so....so is at least as better as a proper Crown Macrotech from this point of view but now is stabile and no more fried op amps on my BGW's.
@@emilvladoiu91 blown outputs generally from overloading the output. Many of those faults with the op amps were not because of over voltage due to the design they were over voltage due to the zener diode failing and going open, or the solder connections to the zener breaking down due to thermal stresses from repeated heating and cooling. When the connection fails the zener might as well not be there and full supply voltage kills the op amp. When I was in the business I saw so many failed amps that were caused by broken solder connections in the driver stage. Changing to a lower voltage zener won't do you any good if the zener goes open or the solder fails on it. This app had no problem in the amplifier board the problem ended up being on the relay. Broken solder the number one problem with most electronics. Cracks solder or cold solder is the number one cause of component failure other than user error for example shorted speaker wires.
Its good that you give the warnings of dangerous high voltages for the safety of other people with little to no knowledge of electrical equipment.
Me I Don't Mess With That Old
Obsolete Stuff. I EOL It
@@rogertyler3237 You might not but a lot of people still do.
I used to work on these death traps. Once I had a TO95 transistor blow into my forehead which left an impression for weeks, much to the amusement of my fellow technicians. As I'm sure you know, always be extra careful when working on such beasts as they don't give second chances. Loved and subbed the channel BTW!
I was once thrown across the shop my a microwave power supply. Everyone laughed.
Hearing & experiencing things like that is always fun, right!?!?…NOT!!
In the very few repairs I've tackled, I've found a good solder re-flow will work wonders on older equipment. Excellent vid!
Yes likely a bad connection. More than likely the plug.
Yep, i got a Sega Genesis for $5 and fixed it by reflowing
I was 10 years old in 1974. I remember going to see Earthquake in "Sensurround" at the theaters and the seats did indeed shake. Little did I know that these were the amps used.
Yup, lots of them.
I worked in a big London West End Cinema when Earthquake was first shown.
The film company sent a couple of engineers to install the Speaker and Amplifier.
The sound was phenomenal. I often wondered if it would dislodge the old plaster ceilings when the films were shown.
I watched earthquake way back, the sound was amazing. The whole theater shook.i was told it's a separate audio track triggered off the movie sound. I loved it and sad it will never come back.
Watching this in England at 3 in the morning, love your videos.
I'm watching this in Wales at 3 in the afternoon :)
I worked for Automated Processes inc (API) in the 1970's. We made recording consoles for studios. We also made some amps for Sensoround used for Earthquake.
Wow i finally found someone who speaks english who deals with home theater and commercial amps and not car amps. will subscribe
I have a bgw 500d, I call it the "arch welder" 😂 I made a buddies house power dim with every bass punch during a New year's party. The only repairs I've made were changing out the big resistors as they do get very hot and I've had one burn up, not now with 10watt flame proof one's 👍. Get amp for sub channels with the high distortion as it's not as noticable.
I also just remembered I had a similar issue with the plug connector having slight oxidation from living in the West coast of BC. Terminal fretting. Cleaned terminals and installed dielectric grease, all good now.
Good job 👌 keeping the brute going 😁
Brian Gary Walkner graduated from Alexander Hamilton High in maybe 1966-1968. My friend Jon Prudeaux who created his own company Crest Audio was one of the Engineers then. BGW was in Culver City California. They were the first company to use a Crow-Bar circuit to protect the Output Transistors. 100% Hand built and soldered Amplifiers.
bgw TRIED TO GET USERS TO REALIZE THAT Crown DC-300 would max out & clip into efficient JBL speakers and burmn out the voice coil .... the trick was to run the amps at SOA safe operating area and NOT to clip them ..effectivlly causing 'DC' across the voice coil.. I sold many of BGWs amps in Illinois & Wisconson back in the 80s . Also the DC300 would blow a final and send the rails to the voice coil ...PUFF causing an out of warranty on the speakers ( JBL ) Our firm represented both JBL & BGW....back when JBL used indepentent sales rep companies...." good ole days"
as far as distortion... I would suggestr you measure ...could be a WAY TOO CONSERVATIVE rating,
Nice to know!
Thanks for that. Crest certainly took things to another level ...ie., robust, BIG power, high damping factor.
Peavey bought Crest if I'm not mistaken.
❤❤❤👏👏👏🔥🥇🌝
Watching this at 12:30pm here in Thailand. Nice amp.
"Earthquake"... Those were the days. I saw the movie in the theater when I was 15 years old. It was a thrill (pun intented). The story was second to none, it was all about the sensurround effect. I remember the great Charlton Heston, aka the mythical 'Ben Hur, playing the role of Stewart Graff, a construction worker in "Earthquake".
I purchased a Universal 8 condensed 20 minute super 8 sound version of that film way back in the early 80’s from a company called Famous Films in Florida. I used to hook my projector speaker out to a cheap solid state guitar amp and crank it to get the rumble effect. And of course I’ve seen the movie in it entirety. Cool movie.
Great Amplifer! The 750G had the best meters! The GTA & GTB were amazing sounding amplifiers.
Nice job. Amazing skills you have!
Thank you Dave you give a warning for the high voltage amplifier.
Great video + bonus history... Thank you.
Good way to effortlessly fry tweeter voice coils (whoops...) It's also easy to short component leads to the heatsink. I pre-cut all the leads through a perfboard when working on these to keep that from happening. It should be able to do 800W into 8 ohms in bridge configuration just before clipping...good for quickly heating a room and overheating the standard 16AWG AC line cord! Time to hook it up again since winter is almost here.
I still can't get over the absolutely mental size of the power transformer and filter caps in these things...back when the purchase price got you a healthy portion of gravitational pull.
The best solid state amplifier ever made. I used to be an authorized warranty station for them back in the late 80's early 90's.
Oh yes they were good. I would take one any day.
Hey Frank, did you go to Chi?
@@jdmccorful No
@@12voltvids I have 2 750B's which have the LED level display. Currently using them in my stereo system with an Ashley 2 way active crossover.
Great amps agreed, but up your life insurance if you're working on them regularly
I enjoy your videos so much thank you very much keep up the good work.
Great job. Though it might also be a good idea to also touchup the solders on the socket for the wiring harness. Might have missed you giving it a good look over and determining it was OK.
Nice to see the boards didn't show signs of overheating - must be well engineered.
The 750 G was the last of those big amps. It had a large led display for output power and thermal light for power supply and heat sink and dc offset lights as well.
You are simply the best. Love your videos!!!! :)
Just wondering if the pins were marking good contact !
That's a lot of T-03's in there. Bet that amp sounded amazing in it's day. 😍👌
Not the cleanest of amps but at 130db who cares.
Not sure how I missed this vid but found it now. These amps are awesome for how simple they are, there's a few similar (but obv. silicon) builds floating around YT where they simply point-point the whole thing together with no PCB or cabinet & I keep meaning to make one one day! At 130dB who's worried about THD numbers anyway, chances are what you're listening to wasn't produced enough to matter. Almost enough to drown out the wails of audiophools :D
Need them all like this!
Why did you not hook it up to your function generator and scope? Not related to this video with its TO-3s, how do you quickly check TO82 BJTs in circuit to make sure that they are probably good?
very nicely diesgned amp
So just re-seating the plug is the only thing you changed. That allowed the relay protection to kick in. So it works again. Nice !😉
""Sensurround"" was this amplifier driving a Cerwin-Vega 18 inch subwoofer model 189 ES they were in a horn loaded cabinet, the type of horn depended on the theater they
were installed in. The number of amps and subs depended on size of theater.
I have seen those wires going into the sound board's cannon plugs come loose from the plug. Maybe could contribute to the fault?
When you disconnect your your speakers, why do you not have to insert a dummy load into the speaker outputs of the amp?
6 minutes in before work even, mind blown.
Most 50''s theater setups for sound were 4 channel magnetic. The channels were left center right and effects.
Nice heavy duty contruction .. no expense
it seems a real good ampliflfier good built
excellent video
i came across a 1970's cerwin vega amp it was being tossed i grabbed it i restored it and most of the output transistors where shorted, came out of a club if i recall
Hi mr good vare good
Thes videoi. Thank you for thes video.
Abdul. Iraq bagdhad
Great video tnx. 👍.
Good work Brother
A big old beast, a brute as you said :-D
Oddly i thought there was a semi short through a mica insulator so the heatsink had power, the heatsink is earthed to the case so it could have leaked.
I've had trouble with mica insulators and a tiny spec of solder :-(
Got several BGWs, my dad had a 1000, their first if I’m not mistaken. I have a 750g from 89’ that just started flashing idle lights on power up I can’t seem to fix. Need someone with some expertise.
I noticed a couple of suspicious 'rings' in the solder connections of the upper row of power transistors (22:35). Probably bad connection due to heat stress. That solder may have been reconnected when you unsoldered/soldered the emittor resistors prior to testing the transistors. Better reflow them all.
Wow, good job.
Just Like Those Old Tube Radio's & Tv's
I managed to collect three of the 500d models over the years. I think they are nicer looking than the 750s, having the brushed aluminum face plates. Supposedly they have less power than the 750s but the schematics for them as far as I could remember were essentially the same. I never knew why they were rated having a little less power.
That amplifier looks so cool ! Vintage electronics is the best, since the qaulity was on whole another level compared to " consumamble electronics" nowadays. Things were built to last nuclear war back then.
And very simple design compared to today's stuff.
Lm318 opamps are still available, maybe obsolete but still available. We used to use many LM308 in geophysical electronics.
Just FYI the LM 318h op amp is all over ebay for about $5-10. They like to take out a positive and a negative output when a channel goes. Will trip relay out if one gets leaky too.
Good job
Cool history movie amp.
Wonder if that type of amp would make a good PA amp for bands or performing arts.
Yes you can beat on it all night. Many clubs and bars use these type of Amps.
I had the same problem 10 years ago, when you listen to quiet music it works perfectly when you turn the volume up under load and heat builds up, some of the end transistors defected and stuck closed and stay closed until the amp is energised and hot. That defect is extremely hard to find ... it took me half week to catch it and test transistors under load separate from the amp to see which one sticks.
No When That Equipment Is That Old
It's Time To EOL It.
Nice beast! Just for a party in small apartment :) . Btw what is the maximum power you can draw from a regular power outlet in North America?
Standard outlet 15 amps for 120v, however there are higher 20 amp circuits for certain applications.
@@12voltvids thanks! In Europe (not UK) it is 3680 VA (230V x 16A).
While the outlets are 15 amps / 1800w it's worth noting that continuous loads can only draw 12 amps RMS. Alec from Technology Connections did a video about Space Heater Nonsense. The short version is they're virtually all rated 1500 watts.
1.5KW
The maximum amount of power you can draw?
𝟭𝟬𝟬𝗮𝗺𝗽𝘀 for a couple seconds.
To avoid nuisance tripping, a breaker will pass extra-ordinary amounts of current for surprisingly long periods of time.
A 20 amp circuit can pass 7-8 times the rated 20amp trip amount, ... for up to a second or more.
It will allow up to 3x the rated amount for up to 10sec or so.
It can allow up to 1.5x, to 2x the rated amount for a period extending as long as 30 seconds!
Thats;
𝟭𝟬𝟬𝗮𝗺𝗽𝘀 𝗳𝗼𝗿 𝗮𝗿𝗼𝘂𝗻𝗱 𝟭-𝟮 𝘀𝗲𝗰𝗼𝗻𝗱𝘀, 𝗮𝗯𝗼𝘂𝘁 𝟲𝟬𝗮𝗺𝗽𝘀 𝗳𝗼𝗿 𝗮𝗿𝗼𝘂𝗻𝗱 𝟭𝟬 𝘀𝗲𝗰𝗼𝗻𝗱𝘀, 𝗮𝗻𝗱 𝘁𝗵𝗲 𝗰𝗶𝗿𝗰𝘂𝗶𝘁 𝘄𝗶𝗹𝗹 𝗮𝗹𝗹𝗼𝘄 𝟯𝟬-𝟰𝟬𝗮𝗺𝗽𝘀 𝗳𝗼𝗿 𝗮𝘀 𝗹𝗼𝗻𝗴 𝗮𝘀 𝟯𝟬 𝘀𝗲𝗰𝗼𝗻𝗱𝘀!
All from a 20 circuit!
is it possible whatever protection circuit it has just needed to be reset somehow and unplugging that channel did the trick?
No, any protection circuit would reset as soon as power removed. These type of Amps don't have any logic. They monitor for any DC voltage on output and if any detected it opens the speaker relay. Once the voltage goes away the relay closes.
Can you imagine going to a movie theater w/out having surround sound!?!? I remember those days….it’s wild to think that.
I haven't been to a movie theater in forever. Last one I saw was die another Day and before that lethal weapon 4 and that was 22 years ago.
@@12voltvids Last one I was at was Avengers End Game….I think.
Dave, Die Another Day is a pretty good James Bond Film….but Connery & Moore are my favorite Bonds.
It’s called the magic touch 🤔
Midway was another movie that used Sound surround.
Might be a good idea to advise the customer against hot-swapping cables or connectors on an absolute brute of an amplifier like this! It's asking for trouble! ⚡
Shame somebody takes your content, slows it down, and says it's theirs. :P ruthless people
Didn't take my content. Took musicbakery royalty Free music and slowed it down and claimed it was theirs. I used that track on a road trip video and got a claim. I disputed it as usual as I have a license to use it.
A big amp like that would be great for subs or the wolfer of a bi-amp design. I'd think low distortion wouldn't be as critical there.
That what they were used for in the movie theatres. Subs where distortion won't be noticed. Actually in any high power application because the ear doesn't detect distortion as easily at high volumes anyway.
3.10 am uk time, COVID victim no sleep I remember seeing earthquake
doing better I hope? that sounds pretty amazing, i can't believe they did all that for a movie
uk here too ray 3am lol
So how exactly does 230 watts per channel end up being 750 watts bridged?
360 wpc @ 4 ohms = 720w @ 8 mono bridged. In reality they did closer to 800w
@@solitaire5142 they do more...this is underated......they are massive 8 ohm amplfiers
Lucky again. Maybe cold solder, maybe oxydation on the plug/socket connection. I hate when the output section blows - it can take with it drivers, predrivers, VAS, voltage bias section 🥴🤬. This one has current limiter, so it would be hard to blow the OS. But try to get parts for some of the older gear, yeah.
Now in the same chassis you can find 5kW of class D, but they're almost unfixable. I heard the N Cores from Hypex, very clean, high resolution amp. And my other friend picked up 2ch Pascals boards to try - integrated PS, bla, bla, but everything SMD.
Yup class D are certainly powerful and efficient. I still prefer the sound from my 40 watt vacuum tube amp. Mind you a tube amp requires very good efficient speakers and these days getting good efficient speakers cost an arm and leg.
I'm surprised you didn't clean up the plug and sockets. I suppose the act of unplugging and plugging them in again would clean up the contacts a bit but why not clean them while you are there especially if you suspected a bad contact? I'm not having a go at you it's just an observation and would love to hear your thoughts on that repair. Keep up the good work.
The mechanal action of unplugging and reconnecting will clean the connection.
@@12voltvids Agreed but a little deoxit a brush and multiple insertions would have helped. Again, I'm not having a go, it's just a thought. I totally respect your work and I bow to your knowledge of older equipment. It's hard to get my true thoughts across in such short conversations without sounding abrupt, I promise you that is not my intention. Peace.
You can still buy the LM318 in that TO-5 metal can style.
Future reference' 1 Balance Compensation-1 2/3 Inputs 4 -V 5 Balance Compensation-3 6 Output 7 +V 8 Compensation-2
If you look at the board it has the layout for dip package.
I don't think everyone will think of that, even if they could clearly see in the video, they'd still have issues? as the pin-out is in a circular orientation. Also if they had a burnt board etc.. having the text with the pin-out would help would it not?
You can also bend the pins of an LM318 TO-5 package to fit its DIP layout.
-- See docplayer.net/docs-images/41/2273859/images/page_15.jpg
this has awesome sound quality, and terrifieing power
You think this thing has power you should see my crest vs900. Now that's power. 450 watts per channel!
@@12voltvids 1985 vs 2019 tech.....hhhmmmmm.....
@@lunam7249 crest vs900 is 1997 vintage.
@@12voltvids 1985 vs 1997 tech.... the guy that started crest, worked as a tech for BGW in the begining...lots of power you have.... sound similar to carver PM900 pro.....that has woofer killing powers!! i think is 450 into 8 ohms x 2 channel like yours...i owned a bunch of crest amps back in the day
@@lunam7249 260x2 into 8, 450 x 2 into 4. 1100 into 2 bridges mono.
You are right the guy that started crest was an engineer with bgw on 70s. Crest was merged into Peavey. Yes it sounds simply amazing and will drive any speakers you can throw at it. It is pretty much unclipable as it has an electronic attenuator that will compress the input for peaks that would normally clip protecting speakers at that extreme power. I have killed a few speaker fuses by accident.
I always liked that earthquake movie.
Indeed!
The real star was the incredible 4x4 Chevy Blazer Charlton Heston drove around.
good amp i owned one
Wow, Dave...I knew you were good but now you've entered the realm of "Magic". Just looking at a piece and laying hands on it is enough for the cure!! Hallelujah. And Thanks...
BTW, it's: .1% THD for 225 watts per channel, 20 to 20,000 hz, both channels driven at full volume, with 2 volts input. Guaranteed no more than...
Anything less, the distortion falls to very competitive numbers. In the .02 and less range. And...anyway, I doubt I'll ever make it sweat that much.
You should hear it drive a pair of Magnepans, a notoriously difficult speaker for an amp to control.
Enough, I'm beginning to sound like I'm defending my girlfriend. Thanks for saving her, Dave
that amp does really around 300wrms into 8 ohms x 2 chann !!😮
I was suspecting a fault on the relay board itself, creating its own 'false protection fault'.
Thank you, I am pulling out my 750c tonight and repairing it!
I remember this music bakery this song
silver micas. nice
The switch to put in mono is likely the problem Clean its contacts
How do you drain the capacitors?
Turn off the power.
@@12voltvids Then why are people always warning you not to shock yourself on capacitors of unplugged equipment? You really do have a way of being an unhelpful smartass.
Any properly designed equipment will have resistors across the caps to discharge them when power is removed. Tube gear is different. They use high voltage and the caps can hold a charge so you need to discharge with a resistor or throw a screwdriver across and draw sparks.
There is a draining resistor mounted on the chassis between the filter caps
@@solitaire5142
This is to protect the op amps from damage from loss of one of the rails. This ensures that both + and - rails are fully discharged.
My theory is that you had a weak solder joint that caved under the surge of that loud "pop". Resoldering fixed it.
Possible or the plug connection failed.
155v? You should see me wondering about attempting to bias my 100w valve amplifier with 460v across the rail!....
That's easy as you are just looking at the voltage drop across the kathode resistor.
How dare that weak breaker trip having to cope with the inrush of that beer can sized filter cap :-).
With the lights on, they draw about 650 watts for the studio lights and the inrush from firing this brute up no wonder the breaker tripped. I have 2 circuits in the garage. Lights and garage opener on 1 and bench on the other. Plus 2 240 plugs for my car charger and heat. Draw lots of amps in here.
OP amp +drivers + parallel output transistors and output current protection and thats it ? Result - distorted sound AF :)
Not the cleanest sound but bipolar transistors like bipolar people are a little distorted anyway.
At 31:44 sounded like a drum solo or something
yeah on 120 volts that'll draw about 6 amps at 750 watts
Inrush is probably closer to 15.
That's assuming 100% efficiency and perfect power factor. In reality around 75% amp efficiency and 0.75 PF is reasonable, so it's more like 12 amps draw. Definitely overkill for a home theater.
@@eDoc2020
Overkill is certainly relative.
However, for subwoofer duty, and to adequately track the big pulses of low freqs that accompany the deepest effects, not overkill at all.
Actually, it's likely inadequate.
To maintain the same dB level, a subwoofer driver requires a 4x increase in excursion for every octave downward. That multiplies quite quickly.
Plus, our hearing requires significant additional dB levels as the freqs extend lower.
For 90dB@40hz, we require 18dB more to hear the same relative loudness @20hz.
18dB = 64x increase in power!
So, especially in the home theater, subwoofer realm, it's not overkill.
that amp can pull around 15 amperes...10 continous...for sure, in music stadium
A good speaker can make an average amp sound great, no amp no matter what the cost can make a bad speaker sound good.
Its not the equipment you use, its how you set it up that matters.
a good speaker and a good bgw amp can make you wet your diaper😂😂😂from pleasure
repair ok best
3000 watts of mosfets!!! 150watts x 12 per channel!
I would of stuck the diagram under the lid for the next time in for repair
I'll give it to the owner.
I really hate when the happens. You don't really know if you actually fixed the issue.
It's a pita when it happens. Suspect it was the connector as that was all that was faulty.
@@12voltvids Very good chance. It is a beast! Love it!
Vintage smd tech :)
The worst failures are when replacing output transistors and have missed to find out a burned kilohm resistor somewhere in the driving circuit or a leakage small transistor or a burned pcb trace that is not visible and when test it blows again with flash light in the fuses along with the short circuit sound.And have lost money with a couple of hours and then start again from zero.Freaking experiences.
Yup always quote double the price for parts just incase they all have to be changed again and get a deposit in advance.
That's why it's a good idea to use a series lightbulb when working on power electronics. It won't protect everything but it should help save the big expensive parts.
I swear I see a cheap 2 prong power brick inside there in the mess of wires.
Yup that is a cheap power brick i put in several years ago to run the quiet fan because the original one sounded like a jet engine.
@@12voltvids as long as it works right lol
Looks like your meter needs a new battery.
Yup it does. Pandemic remember. I avoid going to stores unless i have to. Bas enough i have to work in people's homes with full ppe on.
At least it's a Fluke so it should shut down before it malfunctions. Cheap DMMs like I have read high as the batteries go. I don't know how long it took me struggling with a 5v supply that was reading 8v. I even replaced the TL431 because it wasn't conducting even though the input appeared to be well over 2.5v. After that I've been more careful.
@@eDoc2020
It will be a fluke if it is accurate when the battery gets too low, and no it doesn't shut down but the display starts to fade and then the readings go out.
Youre brave messing with this, one mistake and youre dead
It's really not that bad. I'm a professional remember. I am aware of the risks and take all precautions.
Might As Well Tell The Owner To EOL It
Why would he do that?
@@12voltvids sometimes
Those Old 70's Amps
& Receivers Aren't
Worth Fixing.
If The Parts Are
Obsolete.
I Remember I Had
An Old 7p,s Yamaha Stereo
Receiver The Power Supply Was Bad &
I Called About A New one
& It Cost More
Then It Was Worth. So
So I EOL'D it.
@@rogertyler3237 only when parts unavailable.
@@12voltvids I Found All Kinds Of
Led TV Parts On Amazon. I Didn't
Think They Had All Those Parts.
Well At least I Know Where To Go
To Get A Parts If I Need Them.
Dude...just remove that metal can opamp,fit a new dip8 socket and fit a new opamp,you could use: LM318,LF351n,NE5534 and god knows how many more lol,how to say that you can't fix it if the opamp is dead?!?! Come on man....i moddified my BGW a lot,change also the supply zenners for the opamp with lower voltage as the opamp on these amps ar powered to maximum +-20vcc and in case of a shock they will die,i reduced the opamp voltage in mine to +-5VCC and use a LF351N,no problems ever since,don't you ever say that you cannot fix something,there are thousands of ways to fix something,and these old designs are toys for me,i don't even need schematics for them,so be a pro,not a amature.
Op amp is fine. Not about to change something on spec. Perhaps you would and then change the customer only to have a pissed off customer when it breaks again. I hand back no change because it didn't fail. When it came back it the fault remained long enough to find the fault in the speaker protection circuit. This is why I have very loyal customers that constantly bring me stuff. Because i don't charge them 95 to do a "diagnostic' and even when it works find something to change to justify that charge only to have it break down because that guess didn't fix the intermittent. I only change parts after I can demonstrate the fault or if it is a catastrophic failure. Same as I don't shotgun cap replacements. That is a sure sign of an amateur that doesn't understand how they work and how they fail.
@@12voltvids You can always make them better,if you know the parts,you know the specs then is easy to make them unbreakabile,you should know that op is on is full rated voltage and that will kill him,changeing two zenner wont kill anyone and the opamp will say thank you,but your interest is to get damaged sooner or later...more money for you,i get the ideea,what about the customer?? they have no fking ideea what's inside of a amp or how it works so i really don't care about that,if they know better than me,i suggest them to fix them by themself,none of my amps that i fixed or moddified in the last 15 years failed,not even one of them,good parts ar indeed exepensive,but i respect myself and my work.
@@emilvladoiu91 they are operated at the designed voltage for a reason. Changing to a lower voltage for op amp will also change the charastics of the sound. Running a component at the max spec voltage will not shorten it's life. They have a designed operating voltage and that designed maximum operating voltage is still well below the voltage that will damage the component. Over current on the other hand will damage the device as current equals heat and heat damages parts but you already know this. There is a difference between max operational voltage and absolute maximum voltage. Many designs do operate close to the max operational voltage, right up to the limit. This is where the device is at its most efficient, signal to noise ratio of the highest, linearity at the highest. This is why they run them there. Changing the zener to a lower value because you think that will prolong the life of a part is nonsence. It lowers the dynamic range and the signal to noise ratio. Modders think they can outsmart the engineer that designed it. The engineer did the calculations. The exception is when the engineer makes a design change when a problem crops up and the factory issues a service bulletin.
Then can you explain why more then 80% of the bgw-s faults lays in the faulty op-amp's and blown outputs?? so in your opinion you should drive all the op amps and the semiconductors to maximum voltage....now i see why your amplifiers fails and mine doesn't.
You speak about SNR on a power amp?!? I hope this was a joke....like someone will keep an almost 1kw amplifier as headphone amplifier to keep an eye on SNR ratio.
My goal is to make an amplifier bulletproof,Crown Macrotech's have 100Db SNR,this one have 106Db,do you think that my low voltage op now will loose more than 6Db ??? i don't think so....so is at least as better as a proper Crown Macrotech from this point of view but now is stabile and no more fried op amps on my BGW's.
@@emilvladoiu91 blown outputs generally from overloading the output.
Many of those faults with the op amps were not because of over voltage due to the design they were over voltage due to the zener diode failing and going open, or the solder connections to the zener breaking down due to thermal stresses from repeated heating and cooling. When the connection fails the zener might as well not be there and full supply voltage kills the op amp. When I was in the business I saw so many failed amps that were caused by broken solder connections in the driver stage. Changing to a lower voltage zener won't do you any good if the zener goes open or the solder fails on it. This app had no problem in the amplifier board the problem ended up being on the relay. Broken solder the number one problem with most electronics. Cracks solder or cold solder is the number one cause of component failure other than user error for example shorted speaker wires.