Sae Mark 2600 Power Amp Needs Power And Driver Transistors Help !

[KentTeffeteller]

Hi,

This amplifier has a tendency to be unstable. This was also when they were new. It's also a very difficult unit to repair even for experienced professional technicians. I would heavily recommend that someone repair this one who is expert with SAE equipment. Even I had to farm these units out. No shame in farming out difficult to service gear.

 

[chrislane]

SAE Mark 2500

I have a Sae Mark 2500 can some please help me out with the service manual? I am having difficulty finding one. The unit I have doesn't work and I would like to make it work. My email is rjpc@ymail.com. Thanks in advance Chris.

 

[Rob41]

info

I have a Sae Mark 2500 can some please help me out with the service manual? I am having difficulty finding one. The unit I have doesn't work and I would like to make it work. My email is rjpc@ymail.com. Thanks in advance Chris.

I see this is your first post. Welcome to the forums Chris. You'll find the manual you seek at this site: http://www.jims-sae-site.com/

Google is your friend. :thmbsp:

 

[elara]

Hi markthefixer,

I am looking for DCOFFSET and BIAS setting procedure for my SAE 2300 power amp,

If you reah this, Could you please help me?.

Thanks a lot.

 

[Ralphie1948]

Hi
I have SAE MARK 2600 Power amp.
The amp needs new power and driver transistors:
Which Transistors I can replace to my SAE 2600 ?
Thanks
Erkan

Mort's TV into vintage equipment! Levittown, PA They are great!

 

[Ralphie1948]

Hi
I have SAE MARK 2600 Power amp.
The amp needs new power and driver transistors:
Which Transistors I can replace to my SAE 2600 ?
Thanks
Erkan

Hi:
Give these guys a shot: https://www.mortstvrepair.com/
They keep my SAE gear running smoothly.
Don't let the name fool you. They are vintage gurus!

 

[Dswankey]

@Ralphie1948

I see you're relatively new so welcome aboard and here's hoping you enjoy your time here.

While a nice gesture, the member you quoted and offered a suggestion to posted that 16yr's ago and was and I'm assuming still is from another country in this case Turkiye plus he hasn't posted since 2013

 

[Wingrant]

The 2400's bias adjustment uses a distortion analyzer, instead of measuring voltage across a resistor.

PM me your email address and I will send a 471k .pdf file of the 2400's manual which includes the adjustment procedure.

Would you mind sending me a copy also, about to recap a 2600

 

[llwhtt]

I can send it to you, 2600 schematic and 2500 service manual. Start a conversation with me include your email.

Craig

 

[Wingrant]

Craig, thanks for the manual. Do you (or anyone on thread) knows how to set the Bias on the 2600? I don't have access to a THD distortion analyzer (yet) and was hoping to document current Bias setting before recap so I can ensure I know how to adjust afterward.

In my attempt to understand the settings I have come up with.

All tests are with input shorting pins, and 100W 8 ohm dummy load on speaker outputs at idle but on for 30 min or so. ( i realize they need to be 400W but at this time I'm not pushing amp for full loads)

I will place the model number listed on the 2600 schematic first then number located on the(MK 25/2500 ) circuit board layout found in the 2500 service manual.

DC Offset

Target 0 mV DC (ideally <15mV; anything under 50mV is acceptable to start. Adjust R2 (R37) trimmer pot. - currently R 0.001V / L 0.001V
- so I think this is good.

Adjust Quiescent Current (VA Stage

Adjust trim pot R38 (R22) to get 1.6VDC across the 65 ohm Resistors R35 (24) and Resistor 34 (R23) which are located at the top left and right corners of the pre-driver board below the two side by side capacitors C13. I am currently at 1.35V so I am a little low and will need to raise it to target of 1.6V DC this test is done by placing the meter on each lead of one resistor at a time, not a across the two resistors. So I check R38 and document voltage then check R35 and document the voltage. So I think I understand this and will adjust as needed.

Adjust Bias

This is where I need help. I don't see how you can access the 0.2 ohm (5W) emitter resistors on the output stage, or where they are actually located. Access to these are buried when the amp is back together. I originally thought they were the two (R52)'s that parallel the (L3) chokes. Then after reading more I am suspecting they are R58/R156 and R57/R157 0.2 ohm 5W listed as two (R59)'s on the 2500 circuit board layout.

Target: 10mV DC per channel (range 10-20mV for safe Class AB by adjusting trim pot R62/R152 500 ohm (R61)

Any advise on how to set the Bias using the voltage Method would be very helpful.

1) where is the 0.2 ohm emitter resistors located
2) how do I access them?

Thanks

 

[llwhtt]

Step 7 in the "repairing" section, 2.1VDC collector to collector of Q1 and Q3. These will be the top two transistors on the drive boards, one in front and one in back or left and right when facing the board.

Craig

 

[Wingrant]

Thanks, that is much easier,

So just checked Q1 to Q3 collector (outer case) and have a reading of 2.226 volt so not to far off. This sound correct?

 

[llwhtt]

Close enough unless you really want to get to the trimmer under the motherboard.

 

[Wingrant]

Thanks again, I plan on replacing the trimmer with a multi turn but wanted to make sure I had a clean baseline so if I make a change and it is not working I can undo it if necessary.