petehall347
the brandy coffee man
from what i found on the net yes the original crosses to it .
Model 27 with High DC Offset
- Thread starter Motnick
- Start date
mikepick
Active Member
Mouser has the LM741H in a TO-99 case:
https://www.mouser.com/ProductDetail/Texas-Instruments/LM741H-NOPB?qs=QbsRYf82W3G0muqZ4UBumg==
found it via this AK thread... not sure if the pinout matches, I couldn't find a diagram for the originals.
(Sorry to keep butting in, but I'm a bit Model 27 obsessed at the moment.)
https://www.mouser.com/ProductDetail/Texas-Instruments/LM741H-NOPB?qs=QbsRYf82W3G0muqZ4UBumg==
found it via this AK thread... not sure if the pinout matches, I couldn't find a diagram for the originals.
(Sorry to keep butting in, but I'm a bit Model 27 obsessed at the moment.)
petehall347
the brandy coffee man
i saw the dip 8 are not expensive so could buy a few to try . i know it has adjustment so maybe not so critical . had fun swapping op amps in a pa amp of mine to get offsets down . luckily they are in sockets.. no adjustment pots .
I was also unable to find a datasheet for SC5175G. The service manual lists SC5175G on the schematic, and MC1741G in the parts list. I'm not sure if they have the same pin out or not, but I was able to find a datasheet for MC1741G and the pin out of that part seems to be the same LM741. So hopefully they are all the same.
I need to measure the board spacing, but I think the distance between row 1,2,3,4 and 5,6,7,8 is too narrow to accept the dip 8 directly. I'll measure the PCB spacing tonight and report back.
If the spacing is off, you can get a wire wrap socket and bend the leads to fit. YMMV
petehall347
the brandy coffee man
that is good news .
Yes it is. Thanks a bunch for all of your help with this!
926-LM741CN/NOPB
In an attempt to save a few bucks I took a chance that I could make the dip 8 parts work. The PCB hole spacing is just off enough to make the dip 8 legs too short to fit. In order to get the dip 8 parts to fit the PCB I ended up using the legs of the original op amps and soldered them to the dip 8 pins. This extended the legs and allowed them to fit the PCB holes. I added some short lengths of heat shrink tubing to the legs on the component side. I figured that before I placed a new order for TO-99 parts I could at least use the dip 8 parts to see if the offset issue was corrected. In the end I don't think that the dip 8 parts look bad at all installed this way.
If I had it to do over again I would just bite the bullet and pay for the TO-99 op amps.
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petehall347
the brandy coffee man
they look good . should run cooler like that too . not that they should get hot anyway . looks better than the conversion board would look .
mikepick
Active Member
Yes, they look pretty good! I had a look at the part you used, pretty big price delta vs TO-99. Guess you have to weigh the savings against the time to devise your clever solution. 
On the other hand, you can use the savings to buy Bourns pots for the bias, which should make it easier to set.
On the other hand, you can use the savings to buy Bourns pots for the bias, which should make it easier to set.
I recapped the P400 pre-amp board today. That is the most dramatic difference that I have ever heard from a recap! The before and after really surprised me! This thing is sounding much better now.
H401 and H402 should have 2SC458 and from what I read here on the forum these should always be replaced. I have some KSC1845 on hand, but it looks like someone has already beaten me to these. 2N3903 are installed currently. Are these valid replacements? Not sure if I should leave them or go ahead and install the KSC1845 that I have. What do you think?
H401 and H402 should have 2SC458 and from what I read here on the forum these should always be replaced. I have some KSC1845 on hand, but it looks like someone has already beaten me to these. 2N3903 are installed currently. Are these valid replacements? Not sure if I should leave them or go ahead and install the KSC1845 that I have. What do you think?
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petehall347
the brandy coffee man
i would leave them in there .
Sounds good. I’ll move onto the phono board next then.
I’ve hooked up a TT and spent some time listening and observing before I recap the phono board. I have noticed that the left channel sounds staticy for the first song or so then it performs fine. I let the stereo sit off for an hour so and came back to the same scenario. After the first song the left channel clears up.
Do you think I should go ahead and recap this board, or is a deaper trouble shooting advised here?
Do you think I should go ahead and recap this board, or is a deaper trouble shooting advised here?
