Rebuilding extremely early 700, would love input and assistance.
- Thread starter Saabracer23
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Yeah he has some pretty nice speakers. Really though it’s his money and he can do what he wants with it. Not sure if you read through the thread or not, but he has decided not to go “all out” with this one since it’s a rare very early model which is clearly not as stable as it’s improved version. So as I mentioned earlier he is going to find another 700 with the added outputs and white oak that one and we’ll add protection. My guess is that this one won’t see all that much use, but he still wants it usable.
Used parts? What used parts are you referring to?
Dan
Used parts? What used parts are you referring to?
Dan
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- Halfbiass...Electron Herder and Backass Woof
- Joined
- Jan 14, 2011
- Messages
- 74,890
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
- Joined
- Jan 14, 2011
- Messages
- 74,890
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
- Joined
- Nov 15, 2021
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- near Liverpool, NY
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- Lifelong student / listening = bliss
Dan, they are precious! Looks like twin daughters are a bit of a trend in this forum -- here's my photo, taken in the spring of '89:
This is Stephanie & Melissa, my absolute pride & joy.
NOTE: I took this photo because people used to misunderstand why I worked so hard at my job -- they felt that my focus was misplaced. With this photo I was able to simply explain that I had to take good care of the platform that in turn supported my ability to provide for my family. (!)
Once I put this photo in my cubicle, everyone understood immediately where I was coming from. Probably one of my very favorite photos I've ever taken...it stirs such good memories -- similar to the photo you just shared. :0)
Enjoy the journey -- I can report that at the 33+ year mark, it just gets better & better & better...
davis
PS - Back then, VAX = 32-bit Virtual Address eXtension of the 16-bit PDP-11 family. (And for the gearheads in the audience, check out the twist-n-lock Hubbell power connectors in the background...always wanted to upgrade my D500s to those, just for the visual psyche factor that they would provide... :0)
This is Stephanie & Melissa, my absolute pride & joy.
NOTE: I took this photo because people used to misunderstand why I worked so hard at my job -- they felt that my focus was misplaced. With this photo I was able to simply explain that I had to take good care of the platform that in turn supported my ability to provide for my family. (!)
Once I put this photo in my cubicle, everyone understood immediately where I was coming from. Probably one of my very favorite photos I've ever taken...it stirs such good memories -- similar to the photo you just shared. :0)
Enjoy the journey -- I can report that at the 33+ year mark, it just gets better & better & better...
davis
PS - Back then, VAX = 32-bit Virtual Address eXtension of the 16-bit PDP-11 family. (And for the gearheads in the audience, check out the twist-n-lock Hubbell power connectors in the background...always wanted to upgrade my D500s to those, just for the visual psyche factor that they would provide... :0)
Last edited:
- Joined
- Aug 6, 2019
- Messages
- 34
So, I’ve had the amp up and running for nearly a week now. Got voltages set and all is great, offset is under 5mV regardless of where the gain control is. It’s been rock solid and playing flawlessly, sounds really good actually.
One issue/question I was hoping to get resolved. The owner asked about having LEDs placed in the meters as they’re so dim. They really were, worse than the Kenwood L-09M. He asked about White Oak boards and I was told they wouldn’t work in this version of the amp. So next plan was to go my own route. I built a small rectifying circuit so that the LEDs could at least run on DC. Ive used this same basic circuit a dozen times.
Problem is when you have the volume up a bit and the music hits with some impact the LEDs dim. It’s not all that loud as I’m using a pair of 5-1/4” two ways. Here’s what I did.
rectifier one leg of the AC with a 1N4001 and put a 1000uF cap across the line after rectification. With a load on the line I was getting a bit over 8 Vdc. Instead of putting any type of limiting resistor I figured I’d run three LEDs in series to handle the voltage. I did four groups of three, one group to replace each of the four bulbs.
The original lamps drew 100 mA each, so 400 mA total for the group. The current draw of each LED at 2.8 Vdc (which is what I figure each is running at) is 14 mA or 168 mA for the group which is well under half of the draw of what it was. So it shouldn’t be overloading the winding.
So why is it dimming? Is the 1000 uF cap too small? I’m guessing there is a voltage drop and the cap is too small to prevent it? If so, how big should I go, 2200, 3300, 4700, is there too big? For doing like a single blue led I’ve used 100uF in the past and don’t remember having this issue.
Thoughts would be greatly appreciated!
Dan
One issue/question I was hoping to get resolved. The owner asked about having LEDs placed in the meters as they’re so dim. They really were, worse than the Kenwood L-09M. He asked about White Oak boards and I was told they wouldn’t work in this version of the amp. So next plan was to go my own route. I built a small rectifying circuit so that the LEDs could at least run on DC. Ive used this same basic circuit a dozen times.
Problem is when you have the volume up a bit and the music hits with some impact the LEDs dim. It’s not all that loud as I’m using a pair of 5-1/4” two ways. Here’s what I did.
rectifier one leg of the AC with a 1N4001 and put a 1000uF cap across the line after rectification. With a load on the line I was getting a bit over 8 Vdc. Instead of putting any type of limiting resistor I figured I’d run three LEDs in series to handle the voltage. I did four groups of three, one group to replace each of the four bulbs.
The original lamps drew 100 mA each, so 400 mA total for the group. The current draw of each LED at 2.8 Vdc (which is what I figure each is running at) is 14 mA or 168 mA for the group which is well under half of the draw of what it was. So it shouldn’t be overloading the winding.
So why is it dimming? Is the 1000 uF cap too small? I’m guessing there is a voltage drop and the cap is too small to prevent it? If so, how big should I go, 2200, 3300, 4700, is there too big? For doing like a single blue led I’ve used 100uF in the past and don’t remember having this issue.
Thoughts would be greatly appreciated!
Dan
- Joined
- Aug 6, 2019
- Messages
- 34
Excellent suggestion! Does the resistor get all that warm? I’m guessing if you’re cranking it maybe.
Dan
Thank you so much! Yeah I would work hard for them too! Being their father I know that you have no problem, but do others have trouble telling them apart? Lol, I’m kind of glad I didn’t have identical twins, I don’t need them playing tricks on me, one getting into trouble and blaming it on the sibling to those who don’t know. Very cute children!
Dan
Dan
Thank you so much! Yeah I would work hard for them too! Being their father I know that you have no problem, but do others have trouble telling them apart? Lol, I’m kind of glad I didn’t have identical twins, I don’t need them playing tricks on me, one getting into trouble and blaming it on the sibling to those who don’t know. Very cute children!
Dan