Resistor measures 3.865K ohms. We should be good there.
I did have some fun soldering in some old (yes, older) 220uF Polar Elecs in parallel with both C18 and C24 in one channel. Amp immediately tripped power/breaker. Pulled them out and things work. Whew. 😀
Not sure why yet, but will certainly have a good look before doing anything else in that area. One of the caps may have been bad, maybe I put them in the wrong way (didn't think so), or maybe just the absolute wrong thing to do.
I did have some fun soldering in some old (yes, older) 220uF Polar Elecs in parallel with both C18 and C24 in one channel. Amp immediately tripped power/breaker. Pulled them out and things work. Whew. 😀
Not sure why yet, but will certainly have a good look before doing anything else in that area. One of the caps may have been bad, maybe I put them in the wrong way (didn't think so), or maybe just the absolute wrong thing to do.
I just hang a pair of 47µF 160V electrolytics in parallel with the main filter caps, it makes the bass tighter.
If you go much larger than this you will probably need something smaller in parallel as well.
Bypass caps are best grounded where the speaker current ground returns.
Smaller bypass caps may need a small resistor in series with them to reduce the chance of oscillations, I don't generally bother with them for that reason, they can be very layout sensitive.
If you go much larger than this you will probably need something smaller in parallel as well.
Bypass caps are best grounded where the speaker current ground returns.
Smaller bypass caps may need a small resistor in series with them to reduce the chance of oscillations, I don't generally bother with them for that reason, they can be very layout sensitive.
BGW amp modules
I have experience with the BGW 750's I own 2, send me the modules, I can fix them up for you..
I have experience with the BGW 750's I own 2, send me the modules, I can fix them up for you..
re BGW 750B modules
hi there, I am a Tech, I own 2 BGW 750's, I can help you with them, send them to me I can fix them up.. john (jaw audio)
hi there, I am a Tech, I own 2 BGW 750's, I can help you with them, send them to me I can fix them up.. john (jaw audio)
A friend helped me quickly see what I did wrong. The negative rail cap was installed backwards. Luckily a relatively harmless lesson.
Glad you have gotten these old monsters to work. Don't overlook that big octal connector. Get some Cramolin contact cleaner, spray it in and work the connector in and out a bunch of times. contact rectification can send you on a wild goose chase for component problems when none exist. I actually still have a 750 laying around somewhere as well as a BGW 100 somewhere in my storage taking up space. Oh and be carefull substituting newer higher bandwidth devices as you may get some R.F. oscillations, a scope is really handy here.
Small Film Capacitors?
I've been looking around for some source of small format film capacitors to swap out the elecs on the 750c. I've got a 10uF PP 100v PP cap that works for C1, but C3 is a 50uF 12v cap and I'm not finding anything that fits. I've checked a number of sources including Mauser. There is only 1" of clearance on the board under the C3 cap. Before I give up my search, I wanted to see if anyone had other recommendations. Thanks!
I've been looking around for some source of small format film capacitors to swap out the elecs on the 750c. I've got a 10uF PP 100v PP cap that works for C1, but C3 is a 50uF 12v cap and I'm not finding anything that fits. I've checked a number of sources including Mauser. There is only 1" of clearance on the board under the C3 cap. Before I give up my search, I wanted to see if anyone had other recommendations. Thanks!
No luck on your request.
I used to have some 10µF/63V radial lead films, biggest value I was able to find in that form.
I used to have some 10µF/63V radial lead films, biggest value I was able to find in that form.
So in my reading, I'm at a bit of a quandary.
As I posted above, I replaced all caps with Nichicon Muse KZ polar caps and bypassed them with 0.01uF Vishay film caps - except for C1, which is a 10uF Polypro cap also bypassed with a Vishay.
I'm ordering the 47uF caps to bypass the main elecs and am considering including a few bipolar caps Xicon Axials and Nichicon Muse ES in the order to swap out the polar MuseKZs to improve the linearity.
Now this is getting into an area of much debate and I hesitate to do so, but I would like a few opinions based on this specific design (BGW 750). Is the increased distortion of the bipolar a bigger issue than the non-linearity of the polar for C3? How about C11 & C12?
The second question is whether the 0.01uF is the right bypass and I was thinking about ordering some 0.1uF of the same type/brand. I've heard glowing reviews on the 0.01uF, but I've also read that a larger cap would be necessary for audible results.
Thanks in advance!
As I posted above, I replaced all caps with Nichicon Muse KZ polar caps and bypassed them with 0.01uF Vishay film caps - except for C1, which is a 10uF Polypro cap also bypassed with a Vishay.
I'm ordering the 47uF caps to bypass the main elecs and am considering including a few bipolar caps Xicon Axials and Nichicon Muse ES in the order to swap out the polar MuseKZs to improve the linearity.
Now this is getting into an area of much debate and I hesitate to do so, but I would like a few opinions based on this specific design (BGW 750). Is the increased distortion of the bipolar a bigger issue than the non-linearity of the polar for C3? How about C11 & C12?
The second question is whether the 0.01uF is the right bypass and I was thinking about ordering some 0.1uF of the same type/brand. I've heard glowing reviews on the 0.01uF, but I've also read that a larger cap would be necessary for audible results.
Thanks in advance!
Keeping the thread alive 🙂
I`ve begun a 750B resurrection which is being documented over at Phoenix if anyone is interested.
Look what followed me home
I already have both versions one and two of this series schematics but cant seem to find a service manual, if someone could point me in the right direction, I`d be much obliged.
TIA
I`ve begun a 750B resurrection which is being documented over at Phoenix if anyone is interested.
Look what followed me home
I already have both versions one and two of this series schematics but cant seem to find a service manual, if someone could point me in the right direction, I`d be much obliged.
TIA
This has been an interesting thread and a real walk through the past. At one time I owned a pa system powered by 18 BGW 750 and 500 power amps.
(Amazing to think about in this day and time-I just bought a 3000 watt amp that weighs 8 lb.)
I got into these things pretty deep and still have a couple of 750's in the garage. If anybody needs any additional advise-not so much on modifications but repairs and care and feeding-don't hesitate to contact me.
j.
(Amazing to think about in this day and time-I just bought a 3000 watt amp that weighs 8 lb.)
I got into these things pretty deep and still have a couple of 750's in the garage. If anybody needs any additional advise-not so much on modifications but repairs and care and feeding-don't hesitate to contact me.
j.
I've just opened up a can of worms by reading this post!!! I have a 750C that needs work. I figured I would do the upgrades that everyone has mentioned. I have never been so excited to see exactly what can be accomplished with these old amps. Someone mentioned "Bryston 4B" in a comment. A fellow friend uses a 4B to drive is Paradigm speakers. And all I hear about from him is how his amp is the best. Hoping when I am done with this project, I can shut him up, or at least quiet him down a bit! @JohndNelson- I have one 750C but would like another for running in bridged mode. Are you willing to separate with one of yours? I know they are on Ebay, but who really knows what condition they are in. djk- I now believe you are the "king of knowledge" on these amps!
Michael88,
Glad you've been inspired. I've been somewhat impressed with the mods I applied. I actually have the two channels in a slightly different configuration and was doing an A:B comparison while listening. Life got busy and it's been sitting this way for months (not being used) but I plan to pull it out and listen again this weekend in an effort to make a decision and finish it up. The difference between the channels is the use of bipolar caps. While they will improve linearity, I think the Polar Muse actually sound better. Also, I had originally used a pair of THESE (botique PolyPro caps 😀) at C1. I picked up slightly more expensive caps but I did not notice a big improvement in sound. With space at a premium in the amp where C1 is, I like the non-round shape of these bargain PP caps from Madisound.
Let us know how your overhaul is going.
Glad you've been inspired. I've been somewhat impressed with the mods I applied. I actually have the two channels in a slightly different configuration and was doing an A:B comparison while listening. Life got busy and it's been sitting this way for months (not being used) but I plan to pull it out and listen again this weekend in an effort to make a decision and finish it up. The difference between the channels is the use of bipolar caps. While they will improve linearity, I think the Polar Muse actually sound better. Also, I had originally used a pair of THESE (botique PolyPro caps 😀) at C1. I picked up slightly more expensive caps but I did not notice a big improvement in sound. With space at a premium in the amp where C1 is, I like the non-round shape of these bargain PP caps from Madisound.
Let us know how your overhaul is going.
tpremo55,
Well, here's an update. I now have two bgw 750C amps. Since I didn't have a desoldering station, I bought a hakko 707 desoldering unit. Well, I just can't use my generic $20 soldering gun so I also now have a Hakko 927 soldering station. I've been busy working on other projects and those are now done(well, one isn't totally done-but close enough). I've been looking at the different caps and can't make up my mind which ones to use(brands and quality). Maybe you can help me on this matter, and reading your post, you have(in selecting which caps to use) Also, I am switching out the LM318 opamp to a NE5534 opamp. I will be documenting the modifications in both photos and videos along with the final, completed project. I just acquired a Carver C1 preamp(for free) that I will be updating and upgrading also. As for the Carver ALS speakers(the reason I have the two BGW 750C amps), I am still looking for a replacement ribbon, to no avail. So I may have to try my hand at building a replacement ribbon. I think the speakers are going to be the biggest PITA. BTW- I also just picked up a Mitchell Skeleton turntable, all original, that I need to work on.
Here are some pictures of my recent "findings". I am hoping to have all done by the end of December.
Michael
Well, here's an update. I now have two bgw 750C amps. Since I didn't have a desoldering station, I bought a hakko 707 desoldering unit. Well, I just can't use my generic $20 soldering gun so I also now have a Hakko 927 soldering station. I've been busy working on other projects and those are now done(well, one isn't totally done-but close enough). I've been looking at the different caps and can't make up my mind which ones to use(brands and quality). Maybe you can help me on this matter, and reading your post, you have(in selecting which caps to use) Also, I am switching out the LM318 opamp to a NE5534 opamp. I will be documenting the modifications in both photos and videos along with the final, completed project. I just acquired a Carver C1 preamp(for free) that I will be updating and upgrading also. As for the Carver ALS speakers(the reason I have the two BGW 750C amps), I am still looking for a replacement ribbon, to no avail. So I may have to try my hand at building a replacement ribbon. I think the speakers are going to be the biggest PITA. BTW- I also just picked up a Mitchell Skeleton turntable, all original, that I need to work on.
Here are some pictures of my recent "findings". I am hoping to have all done by the end of December.
Michael
Attachments
Michael F, I just saw and read your post, along with your "look what followed me home". How did your amp come out???
Michael
Michael88, you've been busy collecting. Nice stuff. I need to pick up a quality turntable project one of these days.
BGW OUTPUT TRANSISTORS
Hello All
I was the chief engineer / VP Engineering @ BGW, I see that many of you talk about the transistors. Many were house numbered devices with special selected parameters. Here is some data for you.
2N3053 NPN TO3 RCA
2N3583 / 67570 NPN TO66
2N6211 / 67569 PNP TO66
2N6468 PNP TO66
SJ9215 NPN TO3
SJ9216 PNP TO3
2N6259 NPN HOMETAXIAL TO3 RCA
1B05 NPN TO3 RCA
2N3773 NPN HOMETAXIAL TO3 RCA
2N3773 NPN EPI TO-204 MOT
2N6609 PNP EPI TO-204 MOT
MJE340 NPN (2452A, B, C, D GRADED SEMI MATCHED) TO126
MJE350 PNP (2453A, B, C, D GRADED SEMI MATCHED) TO126
MJE720 NPN (2450 SELECTED 5Vce @ 10ma B>100) TO126 BIAS
MJ15015 NPN TO3 MOT
MJ15016 P NPN TO3 MOT
2SB706 / A PNP NEC
2SD746 / A NPN NEC
UPA74 DUAL MATCHED NPN NEC
UPA75 DUAL MATCHED PNP NEC
Be careful when replacing the output transistors with new devices as the old parts are HOMETAXIAL slow and the current parts are FAST and the compensation needs to be addressed.
I hope this data will help.
Good luck
Duke
Hello All
I was the chief engineer / VP Engineering @ BGW, I see that many of you talk about the transistors. Many were house numbered devices with special selected parameters. Here is some data for you.
2N3053 NPN TO3 RCA
2N3583 / 67570 NPN TO66
2N6211 / 67569 PNP TO66
2N6468 PNP TO66
SJ9215 NPN TO3
SJ9216 PNP TO3
2N6259 NPN HOMETAXIAL TO3 RCA
1B05 NPN TO3 RCA
2N3773 NPN HOMETAXIAL TO3 RCA
2N3773 NPN EPI TO-204 MOT
2N6609 PNP EPI TO-204 MOT
MJE340 NPN (2452A, B, C, D GRADED SEMI MATCHED) TO126
MJE350 PNP (2453A, B, C, D GRADED SEMI MATCHED) TO126
MJE720 NPN (2450 SELECTED 5Vce @ 10ma B>100) TO126 BIAS
MJ15015 NPN TO3 MOT
MJ15016 P NPN TO3 MOT
2SB706 / A PNP NEC
2SD746 / A NPN NEC
UPA74 DUAL MATCHED NPN NEC
UPA75 DUAL MATCHED PNP NEC
Be careful when replacing the output transistors with new devices as the old parts are HOMETAXIAL slow and the current parts are FAST and the compensation needs to be addressed.
I hope this data will help.
Good luck
Duke