• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

BGW 750C output failure

Bigears

Bigears

Manager of my own day
I’m working on a BGW 750C that I received with a blown primary fuse. Turns out it has two shorted outputs on one of the amp boards. One each Motorola 357407A and 2N3773. The rest of the board mounted components test out good. I’m looking for subs and came up with these from Newark, but I’m not sure these are the best way to go, Multicomp 2N6609 and 2N3773. Never heard of Multicomp and don't want an unreliable NTE type substitute. Figure I can trust Newark but not sure...

Here is a link to the datasheet and to the Newark page.

http://www.newark.com/pdfs/datasheets/SSI/67R1070.pdf

http://www.newark.com/multicomp/2n6...lar Products&MER=PPSO_N_C_EverywhereElse_None
 

Attachments

  • BGW 1.jpg
    BGW 1.jpg
    96.7 KB · Views: 68
  • BGW 2.jpg
    BGW 2.jpg
    125.6 KB · Views: 75
Last edited:
Register to hide this ad
Perhaps The OnSemi MJ15024/25 or MJ21193/94 would be a better choice? Just not sure on the Multicomp brand.

BTW, I substituted a pair of NTE pulls as "test" outputs in place of the failed NPN-PNP TO3's and powered it up on the DBT and all is good, measured offset at 4 and 5 mv. So...I just need some ideas on subs and this one is ready to go back into service. :thmbsp:
 
Lovely old brute of an amp, those BGWs. If you're going all out with the output devices, I'd likely go with the proper OnSemi devices. Also, I'd be swapping out all those emitter resistors for each of them, too.

Cheers,

David
 
David, the emitter resistors all test fine and did not suffer any failure when the two outputs died. I'm not in the habit of blanket replacement of resistors unless they have epidemic failures. I may recap this one after I get the ouputs figured out. Are there problems with the emitter's on these?

I have no problem getting the OnSemi's as you suggest, but I'm unsure from my limited understanding of the data sheets what the best sub would be. There may be better matches than the ones I listed as options. What do you think?
 
I left my pile of 750 output modules behind when I moved. My 750B is still rock solid. I used to work for a BGW dealer and bought most of their inventory when they quit carrying BGW...
 
I've had several BGW amps, all the way up to a pair of 750 E models, all with zero issues. This 750C is the first with anything beyond a stuck cooling fan. Some of the most cost effective high power you are likely to find. :thmbsp:
 
Bigears, I generally swap out emitter resistors when redoing the outputs. They may measure ok under a light load of an ohmmeter. I'd want to measure them under load or heated up to see if they're stable.

When there are a lot of paralleled bipolar devices like you see there, you don't want one of them current-hogging if there are unstable emitter resistor(s). Consider it a 'prudent' thing to do but not necessarily 'mandatory'.

Cheers,

David
 
Okay, so for current sharing you think the emitters should be swapped...got it.

Easy and cheap enough. I'm still undecided on which OnSemi output to go with. I need to study the datasheets on the The OnSemi MJ15024/25 or MJ21193/94 and find the best match with the original Motorola 357407A and 2N3773. The only real difference between the two is the Hfe. Either seems a big upgrade from the originals.
 
Hello All
I was the VP Engineering for BGW for 8+years and I designed many of the products. The SJ7394 was the Motorola 2N3773, SOA tested and branded SJ7394. The SJ7407 was the Motorola 2N6609, SOA tested and branded SJ7407. The MJ15022/24 and the MJ15023/25 could be used as a direct replacement. They were used in some custom products, however the $>> than our standard parts.

Yes check the emitter resistors and be careful when replacing them with generic parts as they can act as a fuse. I was very careful to select the resistors. They were tested with 10,000uf charged to 85 volts then discharges through a SCR. The resistor could change value however it could not open. I would recommend an RS5 mil type as they have FAT WIRE and will take an overload and not open. Many cheep resistors use thin Nickel -Chrome wire and they open or change resistance greatly upon overload.

Duke Aguiar 1/16/2011
 
Audioman, thanks for the input. I have this BGW up and running again, but I need to swap out my "test" T-03's outputs for a complete set of the OnSemi MJ15024/25 due to current sharing concerns.
 
Welcome, Audioman, to AK. Thanks for taking the time to post. It is nice to hear from those who were leading the designs of the 70s. As an old bench tech back then, I admired the well-built and designed gear when it crossed my bench.

BGW stands with any of the best.

Cheers,

David

AUDIO1MAN said:
Hello All
I was the VP Engineering for BGW for 8+years and I designed many of the products. The SJ7394 was the Motorola 2N3773, SOA tested and branded SJ7394. The SJ7407 was the Motorola 2N6609, SOA tested and branded SJ7407. The MJ15022/24 and the MJ15023/25 could be used as a direct replacement. They were used in some custom products, however the $>> than our standard parts.

Yes check the emitter resistors and be careful when replacing them with generic parts as they can act as a fuse. I was very careful to select the resistors. They were tested with 10,000uf charged to 85 volts then discharges through a SCR. The resistor could change value however it could not open. I would recommend an RS5 mil type as they have FAT WIRE and will take an overload and not open. Many cheep resistors use thin Nickel -Chrome wire and they open or change resistance greatly upon overload.

Duke Aguiar 1/16/2011
Click to expand...
 
I always do a current sharing test. I lower the line voltage to about 100VAC, and drive the amp between 200Hz and 1000Hz to clipping. Then I check the drop across the emitter resistors for consistency. Acceptable is around +/-5% from the norm.
 
You must log in or register to reply here.
Back
Top Bottom