555 is Pa's schm, as far as I remember
looking at 5800 schematic - that one certainly is - strong resemblance to A75
https://www.firstwatt.com/articles.html
looking at 5800 schematic - that one certainly is - strong resemblance to A75
https://www.firstwatt.com/articles.html
It is working right now, but I still have it in it’s box.
I do plan on running it for a while before doing anything to it since I least want to see if any kind of drifting has taken place and if there’s any issues adjusting it to the specs in the service manual. I definitely want to make sure everything is 100% before I dive in.
Before running it, I will pop off the top and take a nice cursory look inside to see if I can see anything abnormal. Just a smart move I think.
I do plan on running it for a while before doing anything to it since I least want to see if any kind of drifting has taken place and if there’s any issues adjusting it to the specs in the service manual. I definitely want to make sure everything is 100% before I dive in.
Before running it, I will pop off the top and take a nice cursory look inside to see if I can see anything abnormal. Just a smart move I think.
I'd check the emitter resistors before powering it up, then the output DC offset after warm up.
After running it for 20-30 hours, check the power supply ripple. If it's not excessive, the caps are still ok.
After running it for 20-30 hours, check the power supply ripple. If it's not excessive, the caps are still ok.
The 1ohm ones on the output stage? It looks to have mosfets. I agree, a good idea to check them.
3 models: GFA-555, GFA-5800, GFP-750 (Aleph P). My shop was an authorized ADCOM repair center.
I am going through and putting together a BOM for this amp since I cannot find one online and found something I was hoping someone can take a look at to make sure I am not having a bad night.
In looking at the service manual, it shows the below information for the "Main Amplifier PCB".
Transistors:
Q-3, 10, 11, 12 ZTX757
Q-9,13,14 ZTX657
The Problem I found was that the schematic shows:
Q3, 10, 11, 12 are listed as ZTX657 and
Q-9, 13, 14 are ZTX757.
So basically the manual changes the NPN and PNP part numbers around. The schematic shows what I believe is the correct symbol and correct part number for what I found.
Since the service manual is on the first page, if someone has a minute, could it be verified that these part numbers are swapped? I just want to make a correct BOM for this amp.
In looking at the service manual, it shows the below information for the "Main Amplifier PCB".
Transistors:
Q-3, 10, 11, 12 ZTX757
Q-9,13,14 ZTX657
The Problem I found was that the schematic shows:
Q3, 10, 11, 12 are listed as ZTX657 and
Q-9, 13, 14 are ZTX757.
So basically the manual changes the NPN and PNP part numbers around. The schematic shows what I believe is the correct symbol and correct part number for what I found.
Since the service manual is on the first page, if someone has a minute, could it be verified that these part numbers are swapped? I just want to make a correct BOM for this amp.
Good catch.
Q 3, 10, 11, 12 are PNP..... ZTX757
Q 9, 13, 14 are NPN.....ZTX657
https://shoptransmitter.com/blog/what-is-the-difference-between-pnp-and-npn/
Q 3, 10, 11, 12 are PNP..... ZTX757
Q 9, 13, 14 are NPN.....ZTX657
https://shoptransmitter.com/blog/what-is-the-difference-between-pnp-and-npn/
Post #33 is correct. Please study this link.
https://shoptransmitter.com/blog/what-is-the-difference-between-pnp-and-npn/
https://shoptransmitter.com/blog/what-is-the-difference-between-pnp-and-npn/
I got my indicator inputs wrong (the arrow piece).
So it’s basically the schematic itself that is wrong, correct? Make sure I’m not having a bad night. Thanks for the assistance.
So it’s basically the schematic itself that is wrong, correct? Make sure I’m not having a bad night. Thanks for the assistance.
Schematic shows the PNP and NPN in the right places.
The ZTX657 and the ZTX757 labels on the schematic were interchanged.
This is why there's a BOM, so you don't need to put the actual part numbers on the schematic.
There are lots of good reasons not to do that. Making mistakes is one of them.
The ZTX657 and the ZTX757 labels on the schematic were interchanged.
This is why there's a BOM, so you don't need to put the actual part numbers on the schematic.
There are lots of good reasons not to do that. Making mistakes is one of them.
Last edited: