SAE 2600 restoration/recap.....need assistance.
- Thread starter Rob41
- Start date
FootFungus
Super Member
It appears James Bongiorno, the originator of the design for this amp, died a few days ago. He did the Dynaco 400 output stage, GAS Ampzilla line, the original Sumo gear, and more recently the Ampzilla 2000 line.
Rob41
Don't stop believin'
I forgot to mention that. When it arrived in the mail from a Craiigslist purchase that's exactly what I said.
He was one of the most influential people in the industry. May he rest in peace.
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Rob41
Don't stop believin'
latests update
While I'm waiting on the diff pairs and a few other transistors, many thanks footfungus, I decided to see if I could track down the cause of the much lower output on the right channel. I already knew it wasn't the driver or pre-driver boards because I swapped them out and everything behaved the same. I then took readings on the jumper wires going to and from the pre-drivers which tested good. Next, I compared values from the input jacks to where they end up on the meter board and they checked out as well. Not too much left at this point so I checked all of the right channel output devices but they are good as well. I figured I would check out the meter board with the gain switches one more time. This time I was more methodical and do my best to follow the path of the circuit. Turns out another set of wires were backwards. I wrongly assumed twice that since I didn't touch anything on that board that it was good.
At least the good news is that I now have equal volume on both channels.
Once I get the last of the transistors I'll be able to set the bias and DC offset. At that point I should be good to go. I was laughing today thinking how much Time I've spent on this amp compared to how much less time it would have taken a real technician.
While I'm waiting on the diff pairs and a few other transistors, many thanks footfungus, I decided to see if I could track down the cause of the much lower output on the right channel. I already knew it wasn't the driver or pre-driver boards because I swapped them out and everything behaved the same. I then took readings on the jumper wires going to and from the pre-drivers which tested good. Next, I compared values from the input jacks to where they end up on the meter board and they checked out as well. Not too much left at this point so I checked all of the right channel output devices but they are good as well. I figured I would check out the meter board with the gain switches one more time. This time I was more methodical and do my best to follow the path of the circuit. Turns out another set of wires were backwards. I wrongly assumed twice that since I didn't touch anything on that board that it was good.
At least the good news is that I now have equal volume on both channels.
Once I get the last of the transistors I'll be able to set the bias and DC offset. At that point I should be good to go. I was laughing today thinking how much Time I've spent on this amp compared to how much less time it would have taken a real technician.
Rob41
Don't stop believin'
Thanks. Yes, I should have listened better. :ntwrthy: I thought I had that part right the first go around. The second time I tested every point so I could follow the paths and could get my head around the circuit. Many lessons learned on my first rebuild for sure. Lucky for me I didn't blow anything......yet.
""I was laughing today thinking how much Time I've spent on this amp compared to how much less time it would have taken a real technician.""
There is the first wrong thing you said-did.
The people who work fast are the reason we have other techs around that actually fix things right.I also commend you a great job.
There is the first wrong thing you said-did.
The people who work fast are the reason we have other techs around that actually fix things right.I also commend you a great job.
Rob41
Don't stop believin'
The list of things to do before this amp is finished is getting shorter. This evening I received the last of the transistors including the diff pairs (thanks footfungus).
Once I replaced all of the remaining transistors on the right predriver board I fired it up for a test run to see if I could now set the DC offset in the right channel. After letting the amp warm up for about 20 minutes I was able to adjust the DC offset to 3mv. I adjusted the left channel to 7mv.
I can now see why I need to get Bournes multi-turn trimmer pots. I must have had to make 20 small adjustments per side to get the DC offset where I wanted it.
Tomorrow I'll tackle the bias adjustment. I'm still trying to figure out the best way to do this. I've read about getting readings between emitter resistors but this looks to be exceedingly difficult to get at on this amp. The service manual for the SEA 2500 states:
"Carefully adjust the DC quiescent current adjustment by measuring with a voltmeter from +95V (+105V on the 2600) supply to collector of the protection transistor (Q4). It should read 2.1V which is equivalent to a current of 30mA. If not, readjust the Quiescent Current Adj. (R38) for proper reading.
From where I'm sitting, it looks like I may want to figure out how to do their method. Any suggestions would sure be welcome.
Once I get the bias set then I'll be able to readjust the DC offset and I'll almost be done. The only remaining item is still the nagging turn-off thump in the right speaker. I think this may be a relay issue on the protection board though.
Once I replaced all of the remaining transistors on the right predriver board I fired it up for a test run to see if I could now set the DC offset in the right channel. After letting the amp warm up for about 20 minutes I was able to adjust the DC offset to 3mv. I adjusted the left channel to 7mv.
I can now see why I need to get Bournes multi-turn trimmer pots. I must have had to make 20 small adjustments per side to get the DC offset where I wanted it.
Tomorrow I'll tackle the bias adjustment. I'm still trying to figure out the best way to do this. I've read about getting readings between emitter resistors but this looks to be exceedingly difficult to get at on this amp. The service manual for the SEA 2500 states:
"Carefully adjust the DC quiescent current adjustment by measuring with a voltmeter from +95V (+105V on the 2600) supply to collector of the protection transistor (Q4). It should read 2.1V which is equivalent to a current of 30mA. If not, readjust the Quiescent Current Adj. (R38) for proper reading.
From where I'm sitting, it looks like I may want to figure out how to do their method. Any suggestions would sure be welcome.
Once I get the bias set then I'll be able to readjust the DC offset and I'll almost be done. The only remaining item is still the nagging turn-off thump in the right speaker. I think this may be a relay issue on the protection board though.
Hi my name is Michele live in Italy, I would like to repair a SAE 2600 (I state that I am no expert, have a qualified electrician, I can read a diagram and check with the tester resistors, capacitors, transistrors). I replaced all the transistors of the drive and main. I have the service manual of the SAE 2500. I would like to ask the calibration values of the quiescent current and bias. I thank all those who want to help me and advise me in the repair of SAE 2600.
Zarathustra
Active Member
Great job indeed.
Like this amp because it's modular construction wise so you can easily work on one board and you do not need to de solder everything.
Now I learned Rob could do this with his skills I feel much more comfortable that I could do the same with this kind of amp. It's great to have such a forum where you can learn from each other about the things we treasure.
Thanks!
Like this amp because it's modular construction wise so you can easily work on one board and you do not need to de solder everything.
Now I learned Rob could do this with his skills I feel much more comfortable that I could do the same with this kind of amp. It's great to have such a forum where you can learn from each other about the things we treasure.
Thanks!
HelloOkay, so I'm finally getting around to repairing and restoring my SAE 2600. It's been a while and may take a bit to complete depending on when I have to ship out again. This amp has had a very hard life on the road, has undergone previous repairs and looks as though it was stored in a garage for many years. Unfortunately I don't have the money to have it professionally restored, but in spite of my lack of experience I think I will be able to do it justice. I do have basic soldering and schematic reading skills but this will still be a challenging endeavor for me.
This will be my first full on repair and restoration of any audio gear so please be patient with me. My background is as a Merchant Marine Engineer and while I do a lot of electrical work aboard ships, my electronics knowledge however is limited but I think I will be able to manage with a bit of help. Please correct me when I use incorrect terminology etc.
I have just ordered the schematics from Stereo Manuals.com so I can't provide those yet. I won't be using ultra high end caps but will be using high quality caps from Nichicon, Elna, or Panasonic. I will try to stay within the same series on each set of boards.
I have done some preliminary testing of the input(?) and driver boards. On both left channel boards all of the to-3 transistors have been replaced with FET transistors. All of the transistors on all four boards tested good. I have not yet tested the output transistors. I've found two resistors that need replacing and another that although tests fine, appears badly burned. There are a couple damaged traces that look like I will need to solder in a jumper as a replacement.
After repairing and recapping the input(?) and driver boards I'll move onto the relay/protection, main board, meter, and lighting boards as well as checking the output transistors.
I do have several nooby questions I'll post after the pictures. I hope you don't mind. :worried:
Left driver board:
The 62Ω 1w resistor is shot and burned so badly that the boards fiberglass weave is exposed on both sides of the board. The trace underneath is damaged to the point I'll need to solder a jumper in it's place.
This leads me to my first set of questions.
1. Are the orange colored resistors like the one pointed out in the picture flame resistant or otherwise a special kind of resistor?
2. On the right driver board, one of the orange resistors has been replaced with a carbon resistor but I can see that it got so hot that it too has exposed the boards fiberglass weave. Should the carbon resistor be replace with the orange original type?
Left input(?)board:
I believe the grey resistors are called precision resistors? Anyway, of the two circled in the photo, they are both supposed to be 750Ω 5w. The one on the left measures 802Ω and the one on the right measures 734Ω.
Round two of the questions.
3. Is this difference significant enough that I should replace the resistors to achieve closer to the specified 750Ω?
4. I'm I incorrect for testing resistors in circuit?
5. Both of the left boards have had their to-3 transistors replaced with FET transistors, is it acceptable to keep the to-3's in place on the right boards or should they be changed for the appropriate FET replacements to match the FET's on the left boards?
6. There are two pots on each driver board. Are they something I should look into replacing or are they not likely to be bad.
7. All I can read from some very poor schematics is that the rectifiers are rated at 25A. I have some new 50A 1000V rectifiers I could use. Is it critical the ratings for these be exact or will my over rated bridge rectifiers work fine?
I know other issues exist beyond these boards and will deal with them once these boards are up to snuff. If anyone thinks improvements can be made with regard to parts materials/types please feel free to let me know. I am certainly open to making any improvements possible. This amp is really "the one" for me. It is the amp I have wanted since I was in my teens and anything I can do to make it shine I will. Any help or input will be greatly appreciated.
edit:
I just placed an order from Mouser and got all Nichicon FG caps for the boards. I also ordered several resistors but I'm not sure if the types of resistors I ordered are correct. The resistors are pretty cheap so if I need to I'll order the specialized resistors.
As far as the resistors I would suggext using Takman metal film on all resistors except the 2W and above use metal oxide such as TKD brand. PartsConnXion is a good source. Elecrtolytics should always be Audio Grade with or not they are in the signal path. Use Elna Silmic II or Nichicon KA, KZ or Fine Gold. When a trace has been damaged or the eyelet use a bare copper lead 26 or 28 gauge. (Neotech has a high purity copper) Source Sonicrafters.
Anthony