Look what followed me home

Michael F

Michael F

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Nowhere near as pretty as El Magnifico`s, but she will clean up just nicely. I`ve had a soft spot for these amps since their introduction and was thrilled to have been offered this one by an old friend and co-worker. This particular amp came out of a popular live music nightclub here doing 24/7 duty for nearly 25 years straight and judging by the interior, it was never cleaned once (refer to the inside picture, that was taken after vacuuming and a 120 psi blow job) The truly remarkable thing is that it is in stock form having never failed in all this time! I somehow doubt todays amps will be able to make such claims in 2039.
I`ve done a restoration on a first generation 750B a little while back so I`m familiar with them. This one will take some effort but the outcome will be well worth it as it has not seen many actual miles is structurally and cosmetically sound, but quite the tar/nicotine/beer/soft drink filled and God knows what else mess, should be a fun project. I can post my progress if anyone is interested
 

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orange

orange

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BGH? BGR?

Okay, BGH Systems.

You have to make that clear as the logo is hard to figure and I had to do a Google search :)

Why not tell us more about it or point us to a thread you wrote about the first one? We'd love to know about it.
 
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laatsch55

laatsch55

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Michael, I think i speak for a lot of people when i say we would love to see this restoration in all its glory...
 
Elite-ist

Elite-ist

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You have your work cut out for you. I love to hear about pieces that have an interesting history to them.

Nando.
 
Michael F

Michael F

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orange said:
BGH? BGR?

Okay, BGH Systems.

You have to make that clear as the logo is hard to figure and I had to do a Google search :)

Why not tell us more about it or point us to a thread you wrote about the first one? We'd love to know about it.
Click to expand...
Please forgive me, I just naturally assumed everyone was familiar with BGW amplifiers. This is a version two, "B" of the 750 series circa 1981. The original 750A was introduced in 1974 and replaced in 1978 with the all new 750 line which comprised the models B and C. While identical in performance and differing only in the metering,
the B sported a full output power LED display and clip only LED`s for the model C.
They were conservatively rated at 225wpc @ 8, 360wpc @ 4 and 720 @ 8 in mono mode, 20-20k both channels driven.
While not officially 2 ohm rated, that didn't stop anyone from running them that way. Gotta love American Muscle.

It`s unfortunate that the company is no longer in existence, especially after being such a dominant force in the `70s. Their website is still up, check it out it`s a very interesting read.
 
Michael F

Michael F

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Web Police said:
Looks like a Beast. I'd be interested in reading about the Resto too.
Click to expand...
OK then. This will be a two part restoration beginning with a much needed cleaning then I`ll focus my attention on dealing with the cosmetic issues. This will be the most time consuming and labor intensive phase I`m sure.

The second stage will see component changes and upgrades. Because the amp is still functional, only a few signal path and feedback loop caps will be replaced outright.
Those parts are cheap and easy to change out and have a large effect on the sound quality as I had discovered with my last project.
Listening and bench test results will then be evaluated and dealt with accordingly but if this is anything like my last project, the aforementioned caps and a few tantalums were all that was really needed to be replaced.
I suppose a full-on component upgrade can be done sometime in the future as well, a nice and clean chassis will make things that much nicer and worthwhile, I just don't want to get too ahead of myself just yet.


And as always, your input, comments and recommendations (not to mention encouragement) are most welcome!
 
Michael F

Michael F

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A few more "before" pics.

One of the things that made these amps so popular is that they are very easily serviceable both in the field and on the bench thanks to the top mounted heatsink modules that hold the output transistors and drive electronics.
Six screws and it`s out. Unplug the circular electron tube type 11 pin connector umbilical, replace module and your back in business in a matter of minutes. Brilliant design.
 

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Lazarus Short

Lazarus Short

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The modular design and the tube-era-style umbilicals are slick, and those are very early balanced inputs, yes?
 
Michael F

Michael F

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Lazarus Short said:
The modular design and the tube-era-style umbilicals are slick, and those are very early balanced inputs, yes?
Click to expand...
In standard form, both 1/4" and XLR input connectors could accept an unbalanced signal. Accepting a balanced input could only be achieved through the use of the optional balancing transformer. These transformers were plugged into the two circular octal sockets below the XLR`s.
A jumper plug (as pictured) was needed to keep the XLR`s active in unbalanced mode when no transformer was present. The 1/4" inputs were always active and remained unbalanced regardless.
It`s interesting to note that this amp is wired pin 3 hot. That was due to no universal pin out standard in the industry at the time which created soooo many problems until a pin 2 hot standard became AES law, but that didn't happen till the mid `90`s.
 
Michael F

Michael F

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The teardown continues. In order to achieve the desired results, I decided to gut the entire amp, there was just no getting around it. Being actively cooled, the odor of 25 years worth of accumulated nicotine and other goodies contaminates my living space in no time when running.

I ran into a few near deal breakers in the process. To access the input attenuators, the front panel needs to be removed. That is quite the chore under ideal conditions owing to the locations of the hardware holding things together. In this case, galvanic corrosion set in to a few places. There are countersunk hex bolts directly on the faceplate so extreme caution needed to be exercised not to trash the near perfect faceplate. The other hurdle was that the volume knob still present had the set- screw cross threaded at some point. There was just no practical way of removing the knob without the risk of damaging the faceplate.
I intended on keeping the original stepped ALPS pots, but they would have needed a complete disassembly in order to be thoroughly cleaned (with no real guarantee that they would be 100 percent afterwards)

I had planned on removing the faceplate regardless so I reluctantly broke the shaft and ordered up some nice Honeywell Mil spec pots as replacements. Probably just as well because they are after all, in the signal path.
 

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eminence1963

eminence1963

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I don't have the behemoth you have, but I do own and am using these 2 that I got.
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The story on these that I got is they came from a old movie house here locally. They were in use for 4 straight years and were never turned off. They were never serviced as they never shut down or had a problem in the 4 years of use. When I got them I just took off the lid and blew them out reinstalled the covers, and have been using them regularly. There is only one in the pic, there is another I have in the garage using it there.
 
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