i'm still here, but for some reason i don't seem to get an email notification all the time, only once in a while... very strange. i've checked my profile settings and everything seems to be kosher with them, but i often get an email notification every 10 posts or so...
i've been working on an RF project also, so i might have missed a notification between sunday and today...
i think i posted a list a few pages of posts back. i'll check and at least try to link to it. if the list wasn't complete, i'll try to make a complete list. you won't find all of the original devices as some of the motorola parts were discontinued a long time ago, but there are ON Semi replacements for them. the Sanyo and/or Panasonic driver transistors are pretty robust, and other than being direct shorted, rarely have problems. the predrivers have been known to go open occasionally, and need to be "updated" as well, because the originals were discontinued shortly before the amp went out of production (but that has nothing to do with the amp going out of production... APT closed for financial reasons like many other small manufacturing companies during the mid 80's).
i've been working on an RF project also, so i might have missed a notification between sunday and today...
i think i posted a list a few pages of posts back. i'll check and at least try to link to it. if the list wasn't complete, i'll try to make a complete list. you won't find all of the original devices as some of the motorola parts were discontinued a long time ago, but there are ON Semi replacements for them. the Sanyo and/or Panasonic driver transistors are pretty robust, and other than being direct shorted, rarely have problems. the predrivers have been known to go open occasionally, and need to be "updated" as well, because the originals were discontinued shortly before the amp went out of production (but that has nothing to do with the amp going out of production... APT closed for financial reasons like many other small manufacturing companies during the mid 80's).
ok, if i have this right....
these are the original transistors:
Q1, Q4, Q10 = 2SC1345
Q2, Q3, Q7, Q11= MPSD01
Q5, Q6, Q9 = MPSD51
Q8 = 2N3906
Q12= 2N3904
Q13 = MPSU10
Q14=MPSU60
Q15= 2SC2344
Q16= 2SC1112
the list i made back earlier in the thread were for replacements for the discontinued parts.... maybe it's time to compile a more comprehensive list as a text file....
in the meantime, i made a working LTSpice model of the amp which is also useful for testing theories as to "what's causing this wierd problem" as well as seeing how the amp works and testing ideas for enhancements... you will need the transistor models, so that's next on my list of things to find and upload...
these are the original transistors:
Q1, Q4, Q10 = 2SC1345
Q2, Q3, Q7, Q11= MPSD01
Q5, Q6, Q9 = MPSD51
Q8 = 2N3906
Q12= 2N3904
Q13 = MPSU10
Q14=MPSU60
Q15= 2SC2344
Q16= 2SC1112
the list i made back earlier in the thread were for replacements for the discontinued parts.... maybe it's time to compile a more comprehensive list as a text file....
in the meantime, i made a working LTSpice model of the amp which is also useful for testing theories as to "what's causing this wierd problem" as well as seeing how the amp works and testing ideas for enhancements... you will need the transistor models, so that's next on my list of things to find and upload...
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ok, the BJT models, and the readme file for the LTSpice model. notice that the servo and the protection circuits and overload indicators aren't included, just the amp itself. next on my list to add is the servo, then the overload indicators and protection circuit, but those will be added as subcircuits so the amp schematic doesn't get cluttered. the power supply model is a bit of a challenge involving a lot of guesswork, since i have no clue of the inductance, K factor etc... of the power transformer. modeling a "sagging" power transformer is a bit of a challenge in itself...
also, when you have it apart, look for any frayed wires at board connections, especially on the protection board. if the amp's been serviced in the past, it could have frayed the wires and you will spend lots of time chasing broken wires down... i had a wire broken at the prot board drive me nuts. it caused a +25V offset in the affected channel (and with nothing really wrong with that amp board). if you test the amp with the screw next to the input jacks removed, use a clip lead between the input jack ground and the rear panel. some revs of the amp didn't have a ground wire going from the input jack to the ground bar between the PS caps, and lifting the input ground allows the input stages to float, causing offset.
check to see if the display board has a fish paper shield behind it (fish paper being the cardboard the cover on the power transformer is made of, i have no clue where the name comes from). if not, put a piece of plastic or fish paper there to keep the fuse clip on the amp module from hitting the display board and causing the chip to go up in flames (quite literally). i've seen it happen at the factory, it's quite the fireworks show.
check to see if the display board has a fish paper shield behind it (fish paper being the cardboard the cover on the power transformer is made of, i have no clue where the name comes from). if not, put a piece of plastic or fish paper there to keep the fuse clip on the amp module from hitting the display board and causing the chip to go up in flames (quite literally). i've seen it happen at the factory, it's quite the fireworks show.
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Thanks Jed
I suspected a grounding issue with my first amp, the more I compare the two amplifiers, it's obvious #1 has been worked on. Whom ever was pretty sloppy, caps replaced tacked on to leads. and extra caps rigged onto the protect board. Im going to do a thorough clean up on the boards. #2 looks as if it has never been touched. Just a blown output transistor. Im thinking new outputs, possibly drivers. And fresh small caps.
bob
Jed
I have a question for you, the drivers for the APT Q15= 2SC2344
Q16= 2SC1112, Should Q16 be 2SA1011 ??? I have pairs of 2SC2344 and 2SA1011
bob
Thanks Jed, ill go with what i goto
Been feeling like crap last few days, but ill get goin soon. Surruunded by flu...
Guys
My second APT, arrived a week ago, finally got time to look it over.
Missing main fuse and both fuses blown on the right side.
I went on and pulled the outputs, 3 test fine 1 shorted.
So replaced the transistors, with used but known good. and fuses, passed dim bulb test, so fired the amp up for real.
Left offset 1.2mv or so right around 7mv. Ok there, ran it most of the night last night, all day today no problems so far !!!!
Fires up, protect lights go out same time. as far as i can tell working normally.
Gotta start working on #1, alotta work to do on that one, it has been messed with.
But the good thing is I have a good reference amp.
bob
My second APT, arrived a week ago, finally got time to look it over.
Missing main fuse and both fuses blown on the right side.
I went on and pulled the outputs, 3 test fine 1 shorted.
So replaced the transistors, with used but known good. and fuses, passed dim bulb test, so fired the amp up for real.
Left offset 1.2mv or so right around 7mv. Ok there, ran it most of the night last night, all day today no problems so far !!!!
Fires up, protect lights go out same time. as far as i can tell working normally.
Gotta start working on #1, alotta work to do on that one, it has been messed with.
But the good thing is I have a good reference amp.
bob
i've seen that happen... i've seen both fuses blow where a shorted speaker was driven, must have kicked the protection relay a lot, but still didn't take out an output device.... these are pretty "bulletproof" amps...
that's ok, i've been rebuilding my system from a toasted hard drive, so i haven't had a chance to look at the protection board on the APT i'm working on. the relay clicks on immediately, so it seems somethings up with the time delay circuit.
that's ok, i've been rebuilding my system from a toasted hard drive, so i haven't had a chance to look at the protection board on the APT i'm working on. the relay clicks on immediately, so it seems somethings up with the time delay circuit.
Jed
Sounds like it, relay delay, maybe a shorted transistor.
Im gonna change the outputs for new onsemi's on my #1 amp just to be safe.
I have been using the hell out of it since I fired it up, she's never missed a beat.
The #2 bud is pretty much a mess, in good shape but has crap tacked or hot glued all over the boards. Im just gonna rebuild the boards. That way ill know it's going to be reliable.
It looks to me like there is a goofy connection somewhere. someone's sloppy hack.
bob
Sounds like it, relay delay, maybe a shorted transistor.
Im gonna change the outputs for new onsemi's on my #1 amp just to be safe.
I have been using the hell out of it since I fired it up, she's never missed a beat.
The #2 bud is pretty much a mess, in good shape but has crap tacked or hot glued all over the boards. Im just gonna rebuild the boards. That way ill know it's going to be reliable.
It looks to me like there is a goofy connection somewhere. someone's sloppy hack.
bob
not a shorted transistor, because when the left channel had offset, the relay wouldn't turn on...
some of the hot glue may be from the factory. the driver heat sinks got a dot of hot glue on the tabs through the board to keep them from working loose, and the V+/- wires to the fuse clips were hot glued in place after they were maneuvered to null out magnetically induced distortion.
some of the hot glue may be from the factory. the driver heat sinks got a dot of hot glue on the tabs through the board to keep them from working loose, and the V+/- wires to the fuse clips were hot glued in place after they were maneuvered to null out magnetically induced distortion.
Jed
I was thinking, a shorted relay driver, but what you say makes sense.
Thanks, on my amp they made a stab at replacing caps. hot glued in the replacements after they tacked the leads in. I noticed a mix match of caps on the protect board.
I saw the glue on the sinks, figured that was factory the work is neat.
Im getting my cap list together for amp#1 listening to amp #2 I love this thing.
One hell of an amplifier.
bob
I was thinking, a shorted relay driver, but what you say makes sense.
Thanks, on my amp they made a stab at replacing caps. hot glued in the replacements after they tacked the leads in. I noticed a mix match of caps on the protect board.
I saw the glue on the sinks, figured that was factory the work is neat.
Im getting my cap list together for amp#1 listening to amp #2 I love this thing.
One hell of an amplifier.
bob
Basic setup from APT manual.
Guys
Thanks to a bud, I have a little information from the APT service manual.
Apt1 power amp final test of specs.
http://www.mediafire.com/?fh81tnlvkf31d9s
bob
Guys
Thanks to a bud, I have a little information from the APT service manual.
Apt1 power amp final test of specs.
http://www.mediafire.com/?fh81tnlvkf31d9s
bob
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wow, that's really excellent.... i wish i still had the huge box of parts i lost in a move....
one of these days i want to start on an "updated" APT-1, using modern components.... i.e. use the same topology. it's a great design, and so is not "tied down" to using only the original components. Tom Holman said the real challenge was taming the triple darlington's phase shift (lots of miller capacitance there to deal with), but there are some drivers and outputs out there these days that might cure that...
one of these days i want to start on an "updated" APT-1, using modern components.... i.e. use the same topology. it's a great design, and so is not "tied down" to using only the original components. Tom Holman said the real challenge was taming the triple darlington's phase shift (lots of miller capacitance there to deal with), but there are some drivers and outputs out there these days that might cure that...
Thanks J
A modern version of the APT, wow. The original is one hell of an amplifier.
Id like to get my first amp running like it should, I couldn't believe the luck of finding Motorola transistors, I doubt that Ill have to replace many. The amp works, just one channel drooping off. could be a bad connection. Im thinking something simple.
Like you were saying in a previous post, a bias prob. Im leaning that way too.
The real work is cleaning up after whom ever worked on it before, cleaning up crappy soldering replacing caps.
I want to get it back to original condition. Good for another 30 years.....
bob