that's the correct output devices for an APT-1
the original ones after some time in 1979 also say APT on them, and they were all that way until sometime in 1983 or 84. between 79 and 83 or 84, APT had the transistors preselected for Hfe<35 by Motorola, and had APT printed on them. the Cce of a genuine MJ15022 should be about 500pf with 10V applied to the collector. Cce (also seen in data sheets as Cob (capacitance with the base open)) has a fairly close relationship to die size. any date code after 9932 should have the logo of (ON) instead of (M) (the date that MOT "spun-off" ON was 06AUG99).
if you're going to sort 15022/23 or 15024/25 transistors by beta, i recommend building a pair of current sources (one operating from a positive supply, one operating from a negative supply) set to 1mA. using a collector supply of 30V, and feeding the base with a current source, you should have a collector current of between 20-35mA you should do this with the device on a heat sink, and a 30 ohm 10W collector resistor to limit the current to 1A if the beta is much higher. if anybody wants a schematic of the current sources and how to connect the transistors for testing, let me know.
the original ones after some time in 1979 also say APT on them, and they were all that way until sometime in 1983 or 84. between 79 and 83 or 84, APT had the transistors preselected for Hfe<35 by Motorola, and had APT printed on them. the Cce of a genuine MJ15022 should be about 500pf with 10V applied to the collector. Cce (also seen in data sheets as Cob (capacitance with the base open)) has a fairly close relationship to die size. any date code after 9932 should have the logo of (ON) instead of (M) (the date that MOT "spun-off" ON was 06AUG99).
if you're going to sort 15022/23 or 15024/25 transistors by beta, i recommend building a pair of current sources (one operating from a positive supply, one operating from a negative supply) set to 1mA. using a collector supply of 30V, and feeding the base with a current source, you should have a collector current of between 20-35mA you should do this with the device on a heat sink, and a 30 ohm 10W collector resistor to limit the current to 1A if the beta is much higher. if anybody wants a schematic of the current sources and how to connect the transistors for testing, let me know.
BTW: Does any one know of a source for a parts list for this amp?
I'm looking at a schematic, in prep for repair and servicing and damm, they didn't bother to label many of the parts
This amp look like it's going to be a bear to t/s and repair, it would be handy to have a list of what the parts are before going in...
thanks
I'm looking at a schematic, in prep for repair and servicing and damm, they didn't bother to label many of the parts
This amp look like it's going to be a bear to t/s and repair, it would be handy to have a list of what the parts are before going in...
thanks
i'm doing some repair work on one this week, as well as a SPICE model, so i can help you with that. i'll have some time tomorrow to sit down and make a list. i thought i poated a list earlier in this thread which transistors were which in the amp module, but i can make a better list tomorrow if you like. i have a fairly comprehensive list started of modern substitutes as well, since some of the original devices are obsolete. i highly recommend you get any MOT/ON parts either directly from ON, or from one of their distributors like Newark or Mouser. AVOID "NOS" parts at all costs!!!! i just did a check of some output devices that came with an amp i'm working on, and the junction capacitances on some of them indicate that they're fakes with about half the die area of the originals (i.e. not 16A devices, but more likely 7A or so devices).
Not sure what I need at this stage, of the four original amps purchased years ago, 3 have the overload led lit on 1 or both channels and the audio is distorted on the indicated channel. Did APT ever release any service documentation for these amps. It would be quite handy when looking at wave forms, voltages etc.
For starters I'm planning to hook up to test bench and put amp under load and trace input signal to output and see how things pan out. I suppose if I wanted to do the job right I'd start out by replacing all the electrolytics caps, but with 4 amps that is a tall order. I sure the testing will provide a bit more info on what I'm up against.
For starters I'm planning to hook up to test bench and put amp under load and trace input signal to output and see how things pan out. I suppose if I wanted to do the job right I'd start out by replacing all the electrolytics caps, but with 4 amps that is a tall order. I sure the testing will provide a bit more info on what I'm up against.
there was a service manual. mine is currently in storage, so i don't have my copy, but i was the amp tech at APT for the last 5 years APT was open, and i remember most of what i knew then. the overload LEDs could be lit because of distortion or offset, since they sample the input and output and compare them. if the servo caps are dried out, it can cause distortion because the servo begins responding to audio and tries to "correct" for it. the electrolytics in the current sources and cascodes are other possible causes of distortion. if you hear any hum in the output, the filter caps for the +/-12V and the +/-75V could be dried out. the big 15000uf main filter caps could dry out, but that's rare.
for checking waveforms, etc..., you should run the amp without a load for most of your testing, and only run with a load when you are testing for forms of distortion that show up with a load and for doing tests like the final bias adjustment which requires running the amp into a distortion analyzer with a load.
there also are other things you might want to assemble, such as:
1) a twin banana plug with an 8 ohm 5 watt resistor across the pins for discharging the filter caps. the distance from the end of a fuse clip to the ground grommet on an amp board is the same as the distance between the pins of the banana plug. ALWAYS discharge the filter caps before working inside the amp. adding a couple of 4.7k/2W resistors across the main filter caps might not be such a bad idea if you have the amp apart. this would give 70 seconds for a 63% discharge, and basically about 3 minutes to get down to about 5V or less, and the power supply won't "notice" the extra 14ma loading.
2) a pair of "dummy" output transistors. remove the covers from a pair of dead TO-3 transistors. clip the bond wires from the B-E pins that go to the silicon chip. solder a 1500 ohm/2W carbon comp (or metal film, but NOT wirewound) between the B-E pins. with the output devices removed and the "dummy" transistors in place of an NPN and a PNP output, this completes the feedback loop and provides a load for the driver transistors. do NOT operate into a speaker load (real or dummy load) with these dummy transistors in place. these dummy transistors will allow you to do waveform and DC troubleshooting of the amp module without risk of torching output devices.
3) a 5.2 ohm dummy load using an 8 ohm 50W resistor that has an adjustable band terminal. this is for adjusting the load impedance indicator.
4) a dual banana plug with a 12ga copper wire across the pins. this is for testing the protection circuit operation by simply plugging it into the speaker jack with signal applied
5) a BIC pen body with two 1/8" notches cut into the large end. this is for manipulating the power supply wires to null out magnetically induced 2nd harmonic distortion.
6) if you plan on doing the noise and hum test, you will need a pair of RCA plugs terminated with 1k resistors to plug into the input terminals..
for checking waveforms, etc..., you should run the amp without a load for most of your testing, and only run with a load when you are testing for forms of distortion that show up with a load and for doing tests like the final bias adjustment which requires running the amp into a distortion analyzer with a load.
there also are other things you might want to assemble, such as:
1) a twin banana plug with an 8 ohm 5 watt resistor across the pins for discharging the filter caps. the distance from the end of a fuse clip to the ground grommet on an amp board is the same as the distance between the pins of the banana plug. ALWAYS discharge the filter caps before working inside the amp. adding a couple of 4.7k/2W resistors across the main filter caps might not be such a bad idea if you have the amp apart. this would give 70 seconds for a 63% discharge, and basically about 3 minutes to get down to about 5V or less, and the power supply won't "notice" the extra 14ma loading.
2) a pair of "dummy" output transistors. remove the covers from a pair of dead TO-3 transistors. clip the bond wires from the B-E pins that go to the silicon chip. solder a 1500 ohm/2W carbon comp (or metal film, but NOT wirewound) between the B-E pins. with the output devices removed and the "dummy" transistors in place of an NPN and a PNP output, this completes the feedback loop and provides a load for the driver transistors. do NOT operate into a speaker load (real or dummy load) with these dummy transistors in place. these dummy transistors will allow you to do waveform and DC troubleshooting of the amp module without risk of torching output devices.
3) a 5.2 ohm dummy load using an 8 ohm 50W resistor that has an adjustable band terminal. this is for adjusting the load impedance indicator.
4) a dual banana plug with a 12ga copper wire across the pins. this is for testing the protection circuit operation by simply plugging it into the speaker jack with signal applied
5) a BIC pen body with two 1/8" notches cut into the large end. this is for manipulating the power supply wires to null out magnetically induced 2nd harmonic distortion.
6) if you plan on doing the noise and hum test, you will need a pair of RCA plugs terminated with 1k resistors to plug into the input terminals..
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Well, I like repairs like this, One of the 10 amp fuses failed, didn't blow mind you just failed, replaced it with a close twin (9 amp) and that amp is back in the race.
Next amp not so lucky, the right channel has a fault condition and the red led remains lit.
I'm working through the schematic and my guess the fault signal comes from the op amp ic tl072 or one of the rc4558 op amp ic's
on the fault board. At least the psu is in good condition, I found out the hard way that the psu caps are alive and well.
This particular amp hasn't been powered up since last night!!!
Nothing like a 90 volt zap across the output trans cases via fingers to remind you to exercise safety precautions.
You'd think the designers would have included a pair of 500 ohm bleeder resistors to eliminate this issue...
I'll put in on my to do list...
My electrician friend says to keep one hand in the pocket at all times, I always thought he was talking about 110/220 vac circuits, but good advice regardless...
Next amp not so lucky, the right channel has a fault condition and the red led remains lit.
I'm working through the schematic and my guess the fault signal comes from the op amp ic tl072 or one of the rc4558 op amp ic's
on the fault board. At least the psu is in good condition, I found out the hard way that the psu caps are alive and well.
This particular amp hasn't been powered up since last night!!!
Nothing like a 90 volt zap across the output trans cases via fingers to remind you to exercise safety precautions.
You'd think the designers would have included a pair of 500 ohm bleeder resistors to eliminate this issue...
I'll put in on my to do list...
My electrician friend says to keep one hand in the pocket at all times, I always thought he was talking about 110/220 vac circuits, but good advice regardless...
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I just noticed you responded to an older post, after I posed a progress report.
I'll study and proceed with caution and more safety.
If you would be interested, I'd be willing to offer $ to have the service manual reproduced.
With 4 of these amps I'm sure to have more drama as time moves on.
Some of your service methods are beyond my skill and possibly service equipment.
Number 5 for example
I'm currently are performing my service using a multi channel tek scope, a tek bench test setup with dwm's and signal generator, a hp attentuator and rms voltmeter. So in many way my skills and abilities are limited
I'm using a pair of 7.5 ohm 10 watt devices to load the amp as I perform testing perhaps unnecessary but still...
Hopefully I won't need to perform all the tests you've indicated, but 1 amp at a time...
I'll study and proceed with caution and more safety.
If you would be interested, I'd be willing to offer $ to have the service manual reproduced.
With 4 of these amps I'm sure to have more drama as time moves on.
Some of your service methods are beyond my skill and possibly service equipment.
Number 5 for example
I'm currently are performing my service using a multi channel tek scope, a tek bench test setup with dwm's and signal generator, a hp attentuator and rms voltmeter. So in many way my skills and abilities are limited
I'm using a pair of 7.5 ohm 10 watt devices to load the amp as I perform testing perhaps unnecessary but still...
Hopefully I won't need to perform all the tests you've indicated, but 1 amp at a time...
APT Pream
Hi felleas! I just got an old APT preamp. Upon inspection, I discovered that it is full of old TL072 op amps. Does anyone have an opinion if substituting these chips with more modern ones will provide sonic improvement? I am thinking of using either OPA 2132 or LM 4552. I especially like the detailled sound of the LM, I already tried this substution on a Sony CD player and the improvement was significant! Do I need to substitute all of them? I am also planning to substitute all electrolitics with Nichicon. Are all or some of them deserving the higher grade caps? Also, should I substitute the rectifiers?
Thak you for any advice.
Hi felleas! I just got an old APT preamp. Upon inspection, I discovered that it is full of old TL072 op amps. Does anyone have an opinion if substituting these chips with more modern ones will provide sonic improvement? I am thinking of using either OPA 2132 or LM 4552. I especially like the detailled sound of the LM, I already tried this substution on a Sony CD player and the improvement was significant! Do I need to substitute all of them? I am also planning to substitute all electrolitics with Nichicon. Are all or some of them deserving the higher grade caps? Also, should I substitute the rectifiers?
Thak you for any advice.
What Electrolitics do you suggest? Nichicon FG, KZ or KW ? Elna? Any suggestion on what type of cap should go where? Where to add the film bypass caps? Which ones?
About the op amps, I just ordere a free sample of 5 units from TI. Any suggestion which one I should substitute (i.e. most critical to sound)? The preamp has 10 072, are they all in the signal path?
I appreciate your suggestions since I am a begginner not very expert in modification upgrades.....
About the op amps, I just ordere a free sample of 5 units from TI. Any suggestion which one I should substitute (i.e. most critical to sound)? The preamp has 10 072, are they all in the signal path?
I appreciate your suggestions since I am a begginner not very expert in modification upgrades.....
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I don't play the capacitor brand game.
Any modern brand name cap will generally out perform a generic 30 year old electrolytic. Once you tack a film bypass in parallel it further reduces differences.
IIRC, all the opamps are in the signal path. The headphone amplifier uses a different unit.
Any modern brand name cap will generally out perform a generic 30 year old electrolytic. Once you tack a film bypass in parallel it further reduces differences.
IIRC, all the opamps are in the signal path. The headphone amplifier uses a different unit.
the headphone amp is an RC4558 or LM4558. the key for that one is the current sourcing capability. the 4558 is ok as a headphone amp, but i'm sure there are more modern devices that can do better. with it's lower output resistance, it's possible that the TLE2072 will work here as well, especially considering that most modern headphones are 120 ohm impedance, vs the more common (in 1980) 8 ohm headphones.
APT-1 Startup
The preamp I got came with a matching amp. It had a broken fuse holder that I replaced. I then connected the amp to a Variac and slowly brought the voltage up. Relay clicked, left channel led became first red then green then red again. Left channel left did not light. At this point I disconnected the amp and discharged both power caps ( I learn the trick by now....). How should I test the amp to see if it really works? I want to avoid doing significant damage....
Input board says Rev 5 and it has 2 47uF caps back to back instead of a 22uF cap as imprinted on the board... Didn't find a rev # on the side board except a "prot" writing.
Thank you for any advice...
The preamp I got came with a matching amp. It had a broken fuse holder that I replaced. I then connected the amp to a Variac and slowly brought the voltage up. Relay clicked, left channel led became first red then green then red again. Left channel left did not light. At this point I disconnected the amp and discharged both power caps ( I learn the trick by now....). How should I test the amp to see if it really works? I want to avoid doing significant damage....
Input board says Rev 5 and it has 2 47uF caps back to back instead of a 22uF cap as imprinted on the board... Didn't find a rev # on the side board except a "prot" writing.
Thank you for any advice...
what's the serial number, i think i can remember the approximate breakpoint for a couple of the revisions
LEDs not lit, no signal, green, some signal, red clipping, distortion or DC but they usually cycle once red,green, dark when powering up.
you can apply a 0.1Vrms signal to the input and look for 3Vrms out with the LEDs green.... no load
LEDs not lit, no signal, green, some signal, red clipping, distortion or DC but they usually cycle once red,green, dark when powering up.
you can apply a 0.1Vrms signal to the input and look for 3Vrms out with the LEDs green.... no load
Test done. The right channel goes though the led changing sequence quickly while the left one is much slower, that is why I thought the right was not working, it changed very quickly... Feeding a sine wave, it goes to the output posts without changes except amplification in the right channel. The left channel led remains red and the sinewave does not go to the output. Rather, there is a weak waveform of much lower frequency that shows the up cycle of the waveform, then on top goes quickly to 0 then stays at 0 almost flat then quickly goes to the bottom tip of the next cycle... Puzzling...
sounds like the cap in the servo (C16) has dried out. i think that amp is a rev2, so it should match the schematic. also replace C1, C26, C27 since those are in the input stage C1 is the input coupling cap, C26 is the filter for the current source supply, and C27 is the bypass for the input buffer emitter loads.