• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

SAE amp / preamp

llwhtt said:
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
Click to expand...
Yes, that was the one. I asked about them working or at least powering on. Took a couple days for reply then they sent me an offer.
 
llwhtt said:
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.
Click to expand...
I had some MJ15034/35’s so I stuck them in. It had the originals replaced with the A913/C1913’s and the HFE they were made me think the MJ’s would be OK. Seems to be working just have to get it adjusted. Too busy today to do anything.
 
hamrules said:
I had some MJ15034/35’s so I stuck them in. It had the originals replaced with the A913/C1913’s and the HFE they were made me think the MJ’s would be OK. Seems to be working just have to get it adjusted. Too busy today to do anything.
Click to expand...
Actually only had to slightly bend the collector, the holes in the board are angled so they almost fit right in.
 
I've never tried something that large, electrically, in that position. Definitely overkill!

Craig
 
llwhtt said:
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
Click to expand...
One side is .825mv the other is .790mv after warm up. I adjusted the bias down to 12.5mv across the two .2 ohm resistors. Letting it run now for a few hours to see how hot it gets.
 
Finally got this 2200 up and running, so with about 10ma thru the VAS transistors, MPSW42/92 with no "SEL" resistor and bias set to .04% THD @ 20KHz, 1W into 8 Ohms the voltage across BOTH emitter resistors is only 4mv for 10ma in the output stage, not much at all. The THD level depends very much on the current in the VAS stage, the lower the current here would require more current in the output stage to get to the .04% THD level and vice versa.

Craig
 
I have to replace the trim pots as one of them is messed up. Just touch it and it goes crazy, it settles back, but it’s a disaster waiting to happen. I’ve got too many SAE oars in the water right now, I’m getting mixed up with parts. I have that 8000 tuner, no idea on that one except I want it working. Can’t say I’ve seen o-rings used before to connect the tuning knob shaft to the “tuner”.
 
All of three of the old school SAE tuners used belts for that purpose. The MKVI/B used o-rings but usually the VIII/8000 had a flat belt for that job at least the ones I've seen. Both my newly acquired VIII and 8000 have been retrofitted with o-rings.

Craig
 
The markings on the unit show 8000, it has a long shaft and at the back end two half roundish grooves and one O-Ring was on and the other had broken from being old and brittle.
 
OK, with the two grooves that one needs O-rings. I have a bunch of VIB O-rings but they are too large for the VIII/8000. Mine need new ones too, I'll take one of mine apart now to see what we need.
 
The cross section of the O-ring is approx. .100" and the inside diameter is approx. 1.8". McMaster-Carr should have something that will work. They also have all of the black oxide hardware if you need any for your SAEs. Many times the Nickel-plated hardware is rusty so I use stainless steel as replacements.
 
Thanks, I’ll take a look. That place is crazy for having all sorts of stuff and in stock. I was looking at a manual I found online and it showed some updates for that tuner too.
 
llwhtt said:
The cross section of the O-ring is approx. .100" and the inside diameter is approx. 1.8". McMaster-Carr should have something that will work. They also have all of the black oxide hardware if you need any for your SAEs. Many times the Nickel-plated hardware is rusty so I use stainless steel as replacements.
Click to expand...
I got some that are 1-3/4” ID with a 3/32” wall. I have to try them yet but they do stretch some so I think they’ll work out.
 
I put the O-rings on, they work great. I plugged it in and it lights up. Looks like the tuning is off by .1, barely. The stereo light doesn’t come on either but the signal strength doesn’t go up a whole lot so I’m sure it needs a bunch of adjustments besides caps and resistors and other stuff most likely. I do like the look of it though.
 
Adjusting the display for correct readout is in the SM. Do you have an antenna connected?
 
Yes I connected up an antenna, one of those cheapies that’s a twin wire. It needs some updating of parts I’m sure and some adjusting.
 
Yesterday I received a 2200 drive board from an ex-SAE employee that couldn't figure out why the left channel wouldn't align correctly. Turns out there was a 1.6KOhm resistor, 1.8KOhm is correct, installed on the + diff collector from the factory. This threw off the current in VAS and made the bias adjustment wonky. Also the electrolytic capacitor across the 51V Zener is silk screened as 25V on the board!!! I'll be using a 63V capacitor. How all of this went unnoticed for all of these years is beyond me.

Craig
 
You must log in or register to reply here.
Back
Top Bottom