SAE 2400

This is really interesting. I have an SAE Mk XXV (or 2500). IIRC, the 2500 was around a lot longer than the 2400, but I've no idea why. It has a fan, but I think it has larger heat sinks than those shown in the pics... OTOH it's been so long since I looked.

Glenn-

Any interest in overhauling an SAE Mk IB preamp, Mk XXVIIB 1/2 Octave Equalizer, Mk VIB Tuner, and the Mk XXV? I can bring them all to AK Fest...
 
We'll need to discuss this...there may be things happening on the job front and I need to get caught up a tad since I'm doing the backstroke in busted gear lately.
 
Once the switches were cleaned, I could see that the relays were shot to hell and doing very bizarre things to the signal. SAE used 48V relays, but I had no luck tracking them down. Not a huge deal...I just converted the circuit to use 24V relays instead. Required swapping out a few caps and resistors. The main dropping resistor went from 1K 3W to 750 ohm 8W (but is dissipating only about 4W). You can see the new relays in the pics, as well as the 8W open-center resistor, chosen to shed heat quickly so it doesn't desolder itself from the PC board.

The relay board was badly hacked, but once I removed the 48V relays I saw why...SAE used some bizarre relay configuration, and the last guy to replace these had no choice but to chop the shit out of the board to fit some standard 'LY2-style' relays in place. Some really creative soldering was necessary to get connection, but it'll work fine.

The DC offset on the amp settles so slowly that even with the 6 or 7 second power on delay, there still is a small DC 'thump' at the speakers. Not much I can do about that. The relay circuit does have provision to disconnect if excessive DC offset is present, but does not have a circuit to open the relays on power off...the relays just open when the circuit discharges. I don't like this, as you get a DC 'thump' (nothing terrible) as the relays open in addition to the 'thump' you get when they close. SAE knew all about this, and even put a 0.1µf 250V cap across the relay contacts!! to help prevent pitting of the contact surfaces. This makes for some real entertainment as the amp is powered down, as the 0.1µf caps act as a signal path for the strangest damn whine as the circuits discharge. I found this unacceptable, and changed the cap to a 0.01µf 250V cap, which dropped the whine down by a good 20db. You can still hear it, but it's only a curiosity now instead of the real eye-opener and embarrassing noise that it was beforehand.

Hey Glen, do you remember which relays you used as replacements?.
If you also remember the changes (the caps, resistors you had to use)?.

Just bought a grrreat condition 2400 but the stock, AZettler's contacts are melted down. They are 48VDC AZ428-56-201 with weird pin layouts...

Thanks!
 
I have no where near the skills needed to do a full on job like you Echowars but here is the little thing that could tell me if I am going to take this on or give up and sell it on ebay broken.

I'm having smoke from the R119 and R112 resistors at power up.
The schematic

http://www.wardsweb.org/audio/docs/M...schematic1.jpg

Or it could be R102 which is the gain circuit and another 1.8k resistor, I cant find the location code on the circuit, I haven't looked hard enough I guess.

I am not wanting to go much further in case someone could tell me if its power supply or something like c113-112 going bad.

The rest of the schematic is
http://www.wardsweb.org/audio/docs/M...schematic2.jpg

Many thanks to wardsweb.

About 6 months ago when I powered it up I had it work for a bit then a little smoke started and I shut it down.
Prior to that, it was sitting idle for years is my guess.

Thanks.
Srinath.
 
Ask to IIWHTT (Craig) here, as Glen (Echowars) Is having perso. problems and don't come here often.
 
If R12 and R19 are BOTH getting hot check CR3, 51V Zener diode, to see if it's shorted.

Craig
 
Not yet, too busy with other work. I did get the heatsink assy attached to the motherboard though. All of the boards are done. Need to get some black RTV for the meter lenses, reassemble the front panel assy and then final assy. Pretty much just mechanical assy now.

Craig
 
Not yet, too busy with other work. I did get the heatsink assy attached to the motherboard though. All of the boards are done. Need to get some black RTV for the meter lenses, reassemble the front panel assy and then final assy. Pretty much just mechanical assy now.

Craig
:beerchug:. I love these amps!.
 
More components are burnt.
Channel B has been rebuilt, has Toshiba's A has SAE transistors.
The .1uf 100V cap on the power amp board next to that connector is also looking sooty.
Further A Channel driver board all the iffy components are all to the left of the big connector.
The 16V 220uf electrolytic looks a bit bulged.
The 750 ohm right below it is burnt, the 62 ohm 1/2 watt dead center right above the big white connector is burnt, 3.9L 1/2 watt resistor looks very iffy, the 62 ohm 1/2 watt further up on the left side is burnt.

That 51V zener dead center of the board is nice and blue and looking good - could still be bad though, but I have not pulled it yet. This evening I will.

Sorry for my lack of observation skills, I had to get the board out to see these cos the transformer was hiding these.

I am thinking of firing it up as a mono to see if B channel is fine. I would likely repeat that repair job on this one.
Are the boards the same ??? Can the board be tested outside the amp with a standalone power source ?

Thanks.
Srinath.
 
I am unable to find location codes on the circuit board, they have put the component values, but not the location code - for example it says .1uf 100V instead of C12 or what not.
Odd, but I should be used to it, this isn't my first failed SAE amp.

Thanks.
Srinath.
 
OK I got the schematic I will electrically identify the components and post back. But how does the amp with B+ of 80v use 16,800 75v Caps ??? or is that a typo in the manual.
Thanks.
Srinath.
 
OK I'll try to swap them after I swap the power transistors out for new ones and replace those components on that board.
However how do I find location codes for this, the board has values of the components but not the component designation. Like it says 62 ohm 1/2 watt but not R112 for example.
I am unable to tell which ones are burnt.
So, C126 or C127 bulged out top, R139 or 140 (750 ohm 2 W), R143 (62 ohm 1/2 w ), and a resistor near the 11-0148 and 11-0149 which is also 62 ohm 1/2 watt and R112 (1.8k 1/2 watt).
Basically 4 resistors and a cap. All on the left side of the board as you're looking at it as it sits in the amp. So that angle section near the back of the amp that's where its all gone terribly wrong. I believe its all on the gain switches side of the thing. So R140, R143, unknown 62 ohm 1/2 watt and R112 plus C126. Either case I have the values, I can replace all of them plus everything on the power amp board. I'd like to test it though so I don't blow outputs again.

Another thing I noticed. The ground pin of the 3 pin plug has been broken off. I am not sure how or when. I could have well broke it, or it may have been broken from before.
All these components are either soldered one leg to ground or have just a cap to ground which will not stop AC.
Also could the gain switches be crudded up to being shorting to each other ?

Thanks.
Srinath.
 
Does this amp really make 80V B+ The schematic has hand written notes on it saying 40v and 39.5v which goes well with the fact that there are 75V 16,000 uf caps for the power supply.
Thanks.
Srinath.
 
The gain circuit seems to play a part in this, and the dead components are all either 1 leg to ground or have 1 cap going bad (C126) to ground. And given that my power cord has a broken off ground pin, is it likely that the burnt components are due to that and a messed up gain switch assy ?
Thanks.
Srinath.
 
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