Caps replaced. Plus also C 11-14. None tested bad on a cap tester. C 26 looks different from the other (blue rather than grey) Is is a special type? Looking at the powes supply, looks different from another amp I had. It has 2 large 1 uF 50V caps that are bipolar (?) plus it has 2 47uF caps back to back while it says 22 uF on the board. Plus, it has two 1uF caps on the board opposite side attached to the IC leads. Will try to power up the amp tonite. If I wrll remember there is a way to test while avoiding replacing and risking to burn out the power transistors?
a 100Wbulb is perfect for powering up an APT-1. to use a variac requires monitoring of the current as you bring it up, especially around 60V when the output transistors normally begin conducting. the light bulb is just so much simpler to use... as well as providing a measure of protection that the variac cannot. we used metered variacs at APT, but after using a light bulb for many years now with a lot of success, it's really the best way to go. an amp operating normally can usually operate at about 90V without any problem, and a normally operating amp should keep the bulb glowing with a dim red or orange glow, about the brightness of a tube filament. with a properly selected bulb (rule of thumb seems to be a bulb wattage approximately equal to the full power rating of one channel of the amp or take the current rating of the line fuse and multiply by 20 [which will work for multichannel amps too]).
the caps might test at the proper capacitance and still be dried out, an ESR meter is the proper tool here.
the only requirement for C26 is that it has low leakage and has low dielectric absorption. not really a "special" type as the electrolytics used in the APT-1 were pretty generic, except for the large power supply caps, which as you can tell by the construction of the amp, they need to have the same form factor, or they won't physically fit in the amp, and have the same connection geometry to accommodate the ground busbar. because of the "sagging" power supply, they also should have the same continuous and surge voltage ratings. that particular type of cap, however isn't prone to drying out like the smaller ones, but it can happen. an ESR meter won't help here. two ways of telling if they're dried out, 1) in extreme cases, the electrolyte may be crystallized and you can hear bits of it bouncing around inside the cap when you shake it. 2) in all cases charge-discharge current measurement. using a 50V power supply, a 100 ohm/2W resistor for charging and a 1 ohm 100W resistor (ceramic wirewound) in series with a 0.01 ohm 5 watt resistor for discharging, charge the cap up to 50V, then discharge it through the discharge test circuit. an oscope across the 0.01 ohm resistor will read the current as 0.01V per Amp. you should be pretty close to 50A peak. any less than 35-40A is likely dried out. the discharger should be connected to the cap through a high current relay (a Ford starter relay works well for this, and is relatively inexpensive).
the caps might test at the proper capacitance and still be dried out, an ESR meter is the proper tool here.
the only requirement for C26 is that it has low leakage and has low dielectric absorption. not really a "special" type as the electrolytics used in the APT-1 were pretty generic, except for the large power supply caps, which as you can tell by the construction of the amp, they need to have the same form factor, or they won't physically fit in the amp, and have the same connection geometry to accommodate the ground busbar. because of the "sagging" power supply, they also should have the same continuous and surge voltage ratings. that particular type of cap, however isn't prone to drying out like the smaller ones, but it can happen. an ESR meter won't help here. two ways of telling if they're dried out, 1) in extreme cases, the electrolyte may be crystallized and you can hear bits of it bouncing around inside the cap when you shake it. 2) in all cases charge-discharge current measurement. using a 50V power supply, a 100 ohm/2W resistor for charging and a 1 ohm 100W resistor (ceramic wirewound) in series with a 0.01 ohm 5 watt resistor for discharging, charge the cap up to 50V, then discharge it through the discharge test circuit. an oscope across the 0.01 ohm resistor will read the current as 0.01V per Amp. you should be pretty close to 50A peak. any less than 35-40A is likely dried out. the discharger should be connected to the cap through a high current relay (a Ford starter relay works well for this, and is relatively inexpensive).
UncleJed,
I just stumbled across this thread. It's been over 10 years since I last saw my Apt gear, my ex got them in the settlement.
I acquired them from Kevin Slowe back in the early 80s. I traded him a Suzuki GS 550 for them. I never asked him where they came from...
I think I'll ask my ex if she's willing to take a nice shiny new receiver in trade for them. I miss the awesome headroom of the Apt power amp.
Thanks so much for the incredibly detailed posts you have made. Your passion is only eclipsed by your incredible memory.
I just stumbled across this thread. It's been over 10 years since I last saw my Apt gear, my ex got them in the settlement.
I acquired them from Kevin Slowe back in the early 80s. I traded him a Suzuki GS 550 for them. I never asked him where they came from...
I think I'll ask my ex if she's willing to take a nice shiny new receiver in trade for them. I miss the awesome headroom of the Apt power amp.
Thanks so much for the incredibly detailed posts you have made. Your passion is only eclipsed by your incredible memory.
Updtes on the APT-1 repair
Well, as advised, I replaced all the caps on the defective board. At testing, bringing up the power slowly with a Variac, the lights became red, then green ( but at diffeent times..)then the good channel one went off while the bad channel one remained reen.
After this I turned off the amp to apply a sinewave to the inputs and test again. This time, when I turned the amp on, both led remained red. Turned off the amp, discharged main caps and tested around. The button rectifier diode bridge on the +- 12 V supply blew up. This happened already on another amp I tried to fix... Any suggestion of what new and improved components I could use? Like low switching noise diodes? While I am at it, I will also replace the Power supply caps. I noticed that there are two 47uF caps in series. Should I replace them with the same or a 22 cap can be used in their place?
Well, as advised, I replaced all the caps on the defective board. At testing, bringing up the power slowly with a Variac, the lights became red, then green ( but at diffeent times..)then the good channel one went off while the bad channel one remained reen.
After this I turned off the amp to apply a sinewave to the inputs and test again. This time, when I turned the amp on, both led remained red. Turned off the amp, discharged main caps and tested around. The button rectifier diode bridge on the +- 12 V supply blew up. This happened already on another amp I tried to fix... Any suggestion of what new and improved components I could use? Like low switching noise diodes? While I am at it, I will also replace the Power supply caps. I noticed that there are two 47uF caps in series. Should I replace them with the same or a 22 cap can be used in their place?
notice that the caps are in opposed polarity. a bipolar cap here would work, but might not fit as space under the protection board is at a premium. this is the time constant for the relay turn-on delay. when a protection fault occurs, the
DC level on the cap goes negative, hence the "bipolar" configuration of the caps. be careful here, the 12V bridge rectifier doesn't usually see much current, it's possible you have a pinched wire somewhere, most likely where something has been disassembled and reassembled (under an amp module, around the display board, etc...)
DC level on the cap goes negative, hence the "bipolar" configuration of the caps. be careful here, the 12V bridge rectifier doesn't usually see much current, it's possible you have a pinched wire somewhere, most likely where something has been disassembled and reassembled (under an amp module, around the display board, etc...)
Amazing that I found this thread because I decided just last night to tear into my defective Apt 1. Perhaps someone can shed some light on what the problem might be. I am not very technically astute, but I know how to read a schematic, solder, measure voltages, etc. My only diagnostic tools are VOM and LCR meter.
The amp powers up and the relay clicks, but there is no output. No fuses are blown. The status indicators turn red then green, but only if the impedance switch is set for 8-16 ohms. When switched to 2-4 ohms, the status indicators turn off completely. If a load is attached to the outputs, the status indicators turn off regardless of switch position. I lifted the power supply board, but I see no discolored or corroded parts.
I would really appreciate any suggestions on how to proceed.
Peace,
Tom E
The amp powers up and the relay clicks, but there is no output. No fuses are blown. The status indicators turn red then green, but only if the impedance switch is set for 8-16 ohms. When switched to 2-4 ohms, the status indicators turn off completely. If a load is attached to the outputs, the status indicators turn off regardless of switch position. I lifted the power supply board, but I see no discolored or corroded parts.
I would really appreciate any suggestions on how to proceed.
Peace,
Tom E
what do the LEDs do when you apply signal to the amp? what you're describing is normal for no input. i only mention it because you didn't mention what your input was. if you have audio going in, the LEDs should light up green. the overload indicator gets it'd signals from 1/2 of the op amp on each amp board. the op amps get their signal directly from the bases of the input transistors. all that separates the bases of the input transistors on the amp boards are a 1k resistor and a 10uf electrolytic cap, and a few inches of RG-174 coax cable. the coax cable is prone to getting pinched under the edge of the amp module if somebody repairing the amp wasn't carefull reassembling it. the 10uf caps could be dried out or open due to age (25-30yrs old....). if you have signal going to the amp boards and the LEDs are lighting green, and can be turned red if you turn the volune up, chances are that the relay contacts are open or oxidized. you can test this by powering up the amp with no input (we used to use rca plugs with 1k shunts in them to do the noise test). disconnecting the load, and measuring from output to ground with a multimeter in DIODE CHECK mode.you should read a very low (near zero, usually around +/- 0.100) conduction voltage at the output terminals. note that this is not an offset voltage measurement. you are measuring the output resistance of the amp, which should be very low if the relay contacts are in good shape. this will not harm the amp, the action you're seeing is a function of the amp's damping factor (actually the meter is inserting a DC current into the amp's output, so it's actually the DC servo that corrects for the meter's current source). if the meter reads open circuit, the relay contacts might be open, or the speaker output wires might have become brittle and broken off the amp boards.
i mention the brittle wires, because i'm in the process of repairing one that's having brittle wires (both 18ga as well as the hookup wire jumpers on the amp boarda) breaking with disturbing regularity and causing all kinds of "stumper" problems ("why is this amp doing this, it wasn't a few minutes ago...)
i mention the brittle wires, because i'm in the process of repairing one that's having brittle wires (both 18ga as well as the hookup wire jumpers on the amp boarda) breaking with disturbing regularity and causing all kinds of "stumper" problems ("why is this amp doing this, it wasn't a few minutes ago...)
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Thanks, uncle jed. I am using audio signal for input, a small speaker for load. There is no output at all. At turn on with no load connected, LED's turn red, then green, but only if impedance switch is set for 8-16 ohm position. If imp switch is set to 2-4 ohm, LED's do not light at all. If amp is already on and LED's are green with switch in 8-16 ohm position, the LED's turn off when switch is thrown to 2-4 ohm position. LED's also turn off when load is connected to output. They never turn red except momentarily at power on; they simply turn off.
In other words, LED's do not light at all with imp switch at 2-4 ohm. They function normally with switch at 8-16 ohm position. They do not function at all in either position if a load is connected. There is no output. This is with an audio signal input.
I know it's nearly impossible to diagnose an amp over the internet, but you sure know this amp well and I thought perhaps you would recognize this problem. Thanks for sharing your knowledge and time.
Peace,
Tom E
In other words, LED's do not light at all with imp switch at 2-4 ohm. They function normally with switch at 8-16 ohm position. They do not function at all in either position if a load is connected. There is no output. This is with an audio signal input.
I know it's nearly impossible to diagnose an amp over the internet, but you sure know this amp well and I thought perhaps you would recognize this problem. Thanks for sharing your knowledge and time.
Peace,
Tom E
it really sounds like you're not getting the input to the amp boards at all.... there aren't very many problems that would cause no audio AND the LED's going out, and no signal getting to the amp boards is the most likely cause. if you read up on the operation of the signal/overload indicators, you will find them a valuable and deceptively simple troubleshooting tool. they are basically miniature distortion analyzers. it doesn't take very much signal to change them from dark to green, so anything they pick up, even a little bit of hum or noise will turn them green. if i were you, i would use something other than a "small speaker" as a load, maybe that small speaker with a 100 ohm 5 Watt resistor in series with it would give you some "elbow room" as far as signal levels go (just in case the amp were to begin working suddenly when you get a signal cable unpinched or whatever)
before you start poking around in the amp, i recommend you go through this thread and re-read the information about discharging the caps..... it can be a painful or startling surprise if you don't discharge them. if you're not careful you can get bit pretty good, or vaporize the tip of your favorite screwdriver (which is one reason you must discharge them with a resistor, because they can very easily make the tip of a screwdriver disappear)...if i ever get an APT 1 of my own, i'm going to add bleeder resistors to the main power supply.... about 4.7k or 10k/2Watt across each of the big caps would be enough to discharge the caps in a few minutes and not impact the operation of the power supply.
before you start poking around in the amp, i recommend you go through this thread and re-read the information about discharging the caps..... it can be a painful or startling surprise if you don't discharge them. if you're not careful you can get bit pretty good, or vaporize the tip of your favorite screwdriver (which is one reason you must discharge them with a resistor, because they can very easily make the tip of a screwdriver disappear)...if i ever get an APT 1 of my own, i'm going to add bleeder resistors to the main power supply.... about 4.7k or 10k/2Watt across each of the big caps would be enough to discharge the caps in a few minutes and not impact the operation of the power supply.
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If I can add a question here, My apt-1 works fine, has a clean output on both channels but on the right channel the led stays red, with or with out a signal. Today I replaced all the electrolytics on the r amp board and on the display board, tomorrow I plan to replace the small value electrol. caps on what I think is called the protector board, it has the 2 rca input connectors on it.
I have a multi channel scope, signal gen and several dvm's with a good understanding (not great) of basic electronic operations and repairs, is there something I should look for?
I have a multi channel scope, signal gen and several dvm's with a good understanding (not great) of basic electronic operations and repairs, is there something I should look for?
On a second apt-1 amp, I think I may have one or more failed output transistors, is a mj15024 & 25 a direct replacement for the mj15022 & 23?
will I need to rebias if I switch
Finally, while the schematic gives you a picture of the circuit layout, it doesn't give you any service or alignment procedures, has any one found service documentation or can provide a link to where I can download it from? thanks
will I need to rebias if I switch
Finally, while the schematic gives you a picture of the circuit layout, it doesn't give you any service or alignment procedures, has any one found service documentation or can provide a link to where I can download it from? thanks
i have a service manual, but it's in storage. there are 3 adjustments, bias, offset and the load impedance sensing circuit. bias is done at 1 watt out, 20khz, adjust with a distortion analyzer until the crossover notch in the analyzer just disappears (too much bias will result in the distortion rising again, as well as too high an idle current). offset is done with the servo disabled (a jumper across the servo's integrating cap), no signal, adjust for +/- 10mv. the impedance adjustment is done at 200hz, into 5 ohm loads, and i think 10Wrms and the impedance switch at 8 ohms. adjust until the impedance light barely lights.
as for the indicator problem, you could have a bad op amp or one of the caps on the display board dried out.
as for the indicator problem, you could have a bad op amp or one of the caps on the display board dried out.
we can rule out caps, I replaced 99% of the elect. caps on the amp board in question, all of the cap on the display board, and most of the caps in the psu/protector board- that appear to have significance. It's possible an op amp has gone bad, but how does one tell? I forced a few to output low using a 33 ohm resistor to gnd and I see changes on the display board. To make the repair ever more difficult is the fact that the circuit boards do not have much in the way of part identification, on the schematic, none of the ic pins are numbered, so I really can tell which op amp I'm looking at. with out a service doc I can measure voltages but I don't know if they are in spec or not. I don't have a distortion analyser, so I can't adjust the bias, even if I knew which pot needed adjustment. The 2 on the amp board are unlabeled, so are the transistors, caps and resistors. Makes tracing the circuit more difficult. Do you know of a source where I can download a service manual?
thanks
thanks
the service manual is not available on the web. the pinout of the op amps is:
1 out A 8 +VCC
2 -in A 7 out B
3+in A 6 -in B
4 -VCC 5 +in B
with no signal, the input and output pins of the op amps on the display board should be at or very near 0V. the same goes for the overload detector side of the op amps on the amp boards (i think it's the B side). the power amp outputs should be within +/- 0.1Vdc. much more than this and the LED for that channel will turn red. the bias pot on the amp board is up near the driver transisistors, the offset pot is down near the input stage or near the op amp.
1 out A 8 +VCC
2 -in A 7 out B
3+in A 6 -in B
4 -VCC 5 +in B
with no signal, the input and output pins of the op amps on the display board should be at or very near 0V. the same goes for the overload detector side of the op amps on the amp boards (i think it's the B side). the power amp outputs should be within +/- 0.1Vdc. much more than this and the LED for that channel will turn red. the bias pot on the amp board is up near the driver transisistors, the offset pot is down near the input stage or near the op amp.
OK, between You and my R2R service manual, I convinced I need a Distortion Analyzer.
I have 2 models in mind the HP 334a or equiv, or a Tektronix AA501 plug in for my tm500 rack.
Any advice on either? I've never used a da so a but of studying ins in order.
I've created a voltage log of the 4 op amps in question, with and with out a signal. I compared the good channel with the one that shows a overload condition. At least now I have a reference to analyse and figure out what to do next. I noticed on the channel in question one side of the op amp that controls the red led has mostly 0 volts in (+ and -) but has something like -4 out. You indicated the op amp could be bad or something else in the circuit could be pulling it negative.
I'll have to see if I can find a replacement set of op amps , I'd like to get original part numbers but maybe NTE has something available
I have 2 models in mind the HP 334a or equiv, or a Tektronix AA501 plug in for my tm500 rack.
Any advice on either? I've never used a da so a but of studying ins in order.
I've created a voltage log of the 4 op amps in question, with and with out a signal. I compared the good channel with the one that shows a overload condition. At least now I have a reference to analyse and figure out what to do next. I noticed on the channel in question one side of the op amp that controls the red led has mostly 0 volts in (+ and -) but has something like -4 out. You indicated the op amp could be bad or something else in the circuit could be pulling it negative.
I'll have to see if I can find a replacement set of op amps , I'd like to get original part numbers but maybe NTE has something available
i think the display op amps are 4558's. the op amps on the amp boards are TL072
NTE replacements for the TL072 are probably TL082's relabeled. the replacements for the 4558's are probably NJM4558. NTE replacements will cost twice what the actual chips cost
looking at the display schematic, if you have 0V on the input and -4V out, you have a bad chip...
NTE replacements for the TL072 are probably TL082's relabeled. the replacements for the 4558's are probably NJM4558. NTE replacements will cost twice what the actual chips cost
looking at the display schematic, if you have 0V on the input and -4V out, you have a bad chip...
Yes, it was a bad chip, the op amp on the amp board.
I had to hit my fav parts store for a few remaining cap and thought I might as well pick up a pair of nte substitutions and now both led are green. Now I get to finish the cap replacement project and wait for a dist. analyz. to arrive. I went with a Tektronix AA501a plugin.
Speaking of electrolytic caps, what is the general consensus on a must replace time frame?
This amp is apx 30 years old, but I think it's pushing your luck, considering the unit cost,
Is 10 years to soon or 25 years too long?
Thanks for your advice in getting this amp back to life, 1 down, 1 to go and 3 to recap ouch
I had to hit my fav parts store for a few remaining cap and thought I might as well pick up a pair of nte substitutions and now both led are green. Now I get to finish the cap replacement project and wait for a dist. analyz. to arrive. I went with a Tektronix AA501a plugin.
Speaking of electrolytic caps, what is the general consensus on a must replace time frame?
This amp is apx 30 years old, but I think it's pushing your luck, considering the unit cost,
Is 10 years to soon or 25 years too long?
Thanks for your advice in getting this amp back to life, 1 down, 1 to go and 3 to recap ouch