SAE amp / preamp

[hamrules]

I ended up with a SAE 2200 amp that’s factory original and now I got a SAE 2100 preamp that looks original except an IC that was replaced on the Phono board. Anyway I hooked up an old Rotel tuner to them and frankly was amazed at the sound. It sounded like HD in analog form. This SAE stuff is crazy good sounding stuff. I’m thinking I should do the electro and tant caps in both and call it a day. Any opinions?

 

[Blue Shadow]

Nah, just use it and learn more. You can rip its clothes off and fondle its parts after you have become more familiar with the units.

 

[hamrules]

Yup, caps it is. I tore down the 2200 last night, besides the million screws, comes apart rather easy. Will check resistors today and found a solder connection that needs fixing. Re-do the thermal paste on everything too. The 2100 after this is back together.

 

[llwhtt]

I just received a 2200 last week from that auction place, wasn't physically as nice as I thought it was though. Found one channel had shorted outputs and the power supply had a couple of broken/shorted diodes. So I completely stripped it and started over. Completely stripped and rebuilt all of the boards. Cleaned all of the sheet metal and parts to be reused.. Replaced those crappy nylon standoffs for the input/driver board with 1/4" aluminum standoffs. Now I can just remove three screws to remove the board instead of wrestling with the nylon standoffs. All hardware is to be replaced also. Waiting for an order to come in to finish it. Another one for the collection.

Craig

 

[hamrules]

I hate those plastic snap in standoffs. I used the same, aluminum, I did try nylon a couple of times and that worked two. There was enough thermal paste on the transistors to do 2-3 units, crazy. Someone was having a bad day. I still have the driver transistors to do, that'll be another bottle of alcohol to get it all cleaned up! I figure I'll just do the caps and down the road when it blows up some day I'll do a strip down and replace it all. Actually I don't run the stuff hard like when I was young so I want to see how long it will go with just new caps, kind of a test. It is a pretty simple one to replace everything. Anyway I always have that UREI 6500 if I want to blow a speaker cone or two.

 

[llwhtt]

If you have noticed the thermal compound gets in the grain of the anodized aluminum and is a PITA to remove, I've tried denatured alcohol, acetone, and lacquer thinner nothing really worked well. A friend gave me a can of LPS NoFlash contact cleaner and it is amazing, removes ALL residue with no elbow grease at all. The only problem is that it is EXPENSIVE. Since I work on a lot of SAE and the heatsinks are very narrow it's hard to do a neat job with the compound so I've switched to various thermal pads. I've been a diehard mica fan for years but finally went to the dark side.

Craig

 

[hamrules]

The dark side, ha ha. Yes the alcohol doesn’t get it out like you stated. I ended up changing the TO220 drivers as they were mixed HFE codes. I’m thinking this was worked on by the factory as it has the 5 year warranty tag on it. There was so much paste I think it acted like a thermal block instead. No joke, there was at least an 1/8” thick around the transistors after they were squished into it. The screws had almost enough on them to do a whole transistor by themselves.

 

[hamrules]

Fired it up today, finally, on the DBT and that bulb flowed so bright I have burned retinas. Anyhow, checking it out I come to realize I switched the outputs, what the heck, how’d I do that! Switched back around and bulb went out and relay kicked in, yippie. Now to set bias, anyone happen to know a MV reading as I don’t have a distortion analyzer.

 

[drumbum]

Fired it up today, finally, on the DBT and that bulb flowed so bright I have burned retinas. Anyhow, checking it out I come to realize I switched the outputs, what the heck, how’d I do that! Switched back around and bulb went out and relay kicked in, yippie. Now to set bias, anyone happen to know a MV reading as I don’t have a distortion analyzer.

Set it to around 10mv.

 

[llwhtt]

I should have mine up and running in a few days, I'll set the bias according to the Service Manual and then try to get an emitter resistor voltage for you. As with most SAE amps they didn't make it easy to do that. James Bongiorno wasn't interested in a particular number to set the bias but to a point where the cross over spike is eliminated OR the 1W into 8 Ohms @ 20KHz for .03-,04% THD method as with most of the SAE amps.

Craig

 

[hamrules]

I should have mine up and running in a few days, I'll set the bias according to the Service Manual and then try to get an emitter resistor voltage for you. As with most SAE amps they didn't make it easy to do that. James Bongiorno wasn't interested in a particular number to set the bias but to a point where the cross over spike is eliminated OR the 1W into 8 Ohms @ 20KHz for .03-,04% THD method as with most of the SAE amps.

Craig

That would be really great. I had it running for like 15-20 minutes as it took that long to settle, unless this is one of those that you have to do within a minute or so of startup, and set it at 30mv for right now but I think that might be too high. The outputs are running around 100 deg F using the heat gun.

 

[hamrules]

Had a tuner playing through it for a couple hours. Sounds good. Shot the heat gun on the outputs and they were 108 deg F, the drivers mounted on the heatsink are just a tad cooler. I’m going to guess the voltage across the two resistors should be about half of the 30mv.

 

[llwhtt]

Are there two empty resistor locations labeled "SEL" on your driver board? Those are for setting the current for the voltage amplifier stage, VAS. Measure the current by reading the voltage across the 68 Ohm resistors. Most of the SAE Service Manuals/Schematics have a voltage but for some reason the 2200 does not. Extrapolating from other SAE schematics I have found that approx. 15ma for the driver stage is common. That would be approx. 1 VDC across one of the 68 Ohm resistors. This has to be set before adjusting the bias using the THD method as it affects the THD quite a bit. With no resistor installed the current will be max and then "SELECTING" the appropriate resistor to get it down to 15ma. Also the rest of the circuit uses some different resistor values compared to other SAE models, I don't know why.

Craig

 

[hamrules]

Are there two empty resistor locations labeled "SEL" on your driver board? Those are for setting the current for the voltage amplifier stage, VAS. Measure the current by reading the voltage across the 68 Ohm resistors. Most of the SAE Service Manuals/Schematics have a voltage but for some reason the 2200 does not. Extrapolating from other SAE schematics I have found that approx. 15ma for the driver stage is common. That would be approx. 1 VDC across one of the 68 Ohm resistors. This has to be set before adjusting the bias using the THD method as it affects the THD quite a bit. With no resistor installed the current will be max and then "SELECTING" the appropriate resistor to get to 15ma. Also the rest of the circuit uses some different resistor values compared to other SAE models, I don't know why.

Craig

 

[hamrules]

View attachment 1567299

I posted a pic of the board. The two resistor spots are open that you talked about. I turned it on and the higher side is under 1vdc. It started at .628vdc and kept slowing going up to .775vdc. I just stopped after that figuring something else must be wrong. The other side started out lower and kept going up also. I have no idea.

 

[hamrules]

This SAE stuff does sound nice but seems to be a pain to work on. It looks simple as heck but is harder than it should be.

 

[llwhtt]

You're fine, turn it on and let it get to equilibrium while monitoring the voltage. This is where the 2200 is an oddball as far as voltages go, this is due to some of the frontend resistor values being different from other models. This voltage is always lower than other models. With no "SEL" resistor in place and low voltage there nothing you can do for now, it will NOT hurt anything, just the THD will be a bit higher. When that voltage is within spec the output stage current will be lower to get to the magic .03-.04% THD. For now just make sure the heatsink is barely warm to the touch. I have yet to see any "SEL" resistors installed from the factory in a 2200. Most of the larger models, 2400, 2500, and 2600 have a trim pot for it. Damn beancounters!

After I get mine up and running with stock values I'll figure out how to make it adjust and act like the other models. This is the first 2200 I've actually got to do my thing. I don't like experimenting on customer units. I'm matching input transistors at the moment. I noticed yours has the dual transistors in the front end, how's your DC offset at the speaker terminals?

Mechanically SAE is a PITA to work on, lots of screws and the output stages are usually buried. Over the years I've just learned to deal with it, SUMOs aren't much better if not worse.

Craig

 

[hamrules]

You're fine, turn it on and let it get to equilibrium while monitoring the voltage. This is where the 2200 is an oddball as far as voltages go, this is due to some of the frontend resistor values being different from other models. This voltage is always lower than other models. With no "SEL" resistor in place and low voltage there nothing you can do for now, it will NOT hurt anything, just the THD will be a bit higher. When that voltage is within spec the output stage current will be lower to get to the magic .03-.04% THD. For now just make sure the heatsink is barely warm to the touch. I have yet to see any "SEL" resistors installed from the factory in a 2200. Most of the larger models, 2400, 2500, and 2600 have a trim pot for it. Damn beancounters!

After I get mine up and running with stock values I'll figure out how to make it adjust and act like the other models. This is the first 2200 I've actually got to do my thing. I don't like experimenting on customer units. I'm matching input transistors at the moment. I noticed yours has the dual transistors in the front end, how's your DC offset at the speaker terminals?

Mechanically SAE is a PITA to work on, lots of screws and the output stages are usually buried. Over the years I've just learned to deal with it, SUMOs aren't much better if not worse.

Craig

Ok, I feel better now. I’ll have to warm it up, it takes around 15-20 minutes or so and then see what that voltage is. The DC offset is like 8mv and 4mv on the channels. For sure, it’s like a sure bet for carpal tunnel taking it apart. I’ve got a 2922, 8000 & a 2400L coming, I’ll be bald. I’m hoping to keep the 2100 that’s here along with the 2400L & 8000 as a set for myself.

 

[llwhtt]

I'm 63 and have never used an electric screwdriver and still no problems with my hands. Did you buy that package deal, 2922 and 8000? I was very close to pulling the trigger on that one.

Craig

 

[llwhtt]

What transistors did you use in the VAS positions, 11-0080A and 11-0083A, the ones you had to twist to fit? I normally use 2SC4793 and 2SA1837 but now I have a stock pile of MPSW42 and MPSW92 that I'm trying is this one, the pin out is the same, EBC, and with a small heatsink attached I hope it will be OK.