I have 2 Altec 9440A amps that have the same problem. The control board fried in both, problem appears to be a stabistor , STB-567. I have researched the heck out of it and came up with 2 solutions. 1 was substituting a MMBD7000 for it and the other was using 2 diodes and a capacitor.
I have searched high and low and can not find that thread where it talked about using 2 diodes and a capacitor.
I'm taking for granted the capacitor is to stop the reverse voltage otherwise I'd think you could just use a Zener or Schottky diode.
Imagine you are talking to a total idiot, tho u don't have to really imagine.
The forward voltage minimum is 1.31v, the max is 1.61v
Could someone please tell me how I get there using the 2 diodes and capacitor ?
I'm not bright enuff to just look at the specs and figure it out but I'm hoping between all of the diodes I have lying around here I can come up with something otherwise I'll order the MMBD7000.
I imagine it gets tiresome helping us not so bright diy'ers, just knoiw it is sincerely appreciated.
I have searched high and low and can not find that thread where it talked about using 2 diodes and a capacitor.
I'm taking for granted the capacitor is to stop the reverse voltage otherwise I'd think you could just use a Zener or Schottky diode.
Imagine you are talking to a total idiot, tho u don't have to really imagine.
The forward voltage minimum is 1.31v, the max is 1.61v
Could someone please tell me how I get there using the 2 diodes and capacitor ?
I'm not bright enuff to just look at the specs and figure it out but I'm hoping between all of the diodes I have lying around here I can come up with something otherwise I'll order the MMBD7000.
I imagine it gets tiresome helping us not so bright diy'ers, just knoiw it is sincerely appreciated.
The stabistor (also called a forward reference diode) is the technical term used to designate a special type of semiconductor silicon diode featuring extremely stable forward voltage characteristics.
Two 1n4148 or your choice of double diode (MMBD7000) diodes should suffice. It is a non critical part from the service manual description and circuit placing, however, why did it fail ... that is important as it may be the 1n4004 (CR2) has failed causing the issue.
Two 1n4148 or your choice of double diode (MMBD7000) diodes should suffice. It is a non critical part from the service manual description and circuit placing, however, why did it fail ... that is important as it may be the 1n4004 (CR2) has failed causing the issue.
I replaced pretty much every component on the board, went with the Dale mil spec metal film resistors. I had read in one thread someone talking about replacing the stabistor with the 1n4148 but said it didn't work - tho he never said whether he tried 2 in series tho
Thanks for taking the time to answer and apparently look up the schematic, is sincerely appreciated
Thanks for taking the time to answer and apparently look up the schematic, is sincerely appreciated
Agree, 2 silicon diodes in series should work perfectly.
Altec used a stabistor only because they were building "the best amplifier in the World" so used the best components available at each points ... but it is not strictly needed.
My doubt is: why do you think they are bad?
Please post a readable schematic or at least the related snippet, I am not downloading 36 MB worth of service manual just to look at that.
Altec used a stabistor only because they were building "the best amplifier in the World" so used the best components available at each points ... but it is not strictly needed.
My doubt is: why do you think they are bad?
Please post a readable schematic or at least the related snippet, I am not downloading 36 MB worth of service manual just to look at that.
The series double diode is used in a lot of amps as a temperature sense component in the driver stack. When the drivers get blown by the output transistors putting rail voltage out the base line, this part can blow. Peavey used a MZ236 for example, no longer available except from them. Two 1n4148 or 1n400x in series is electrically equivalent, but the package is longer.
In my case two 1n4148 in series wouldn't work because the hole in the heat sink for the stabistor was too short to put it in there. I think manufacturers have stopped making stabistors, or distributors stopped stocking them, because a green LED drops the same voltage forwards. Long lead is plus I believe. If you use a green LED, paint it first as they can pick up light and be variable.
In my case some kind diy expert scrapped a Peavey amp and mailed me one.
I looked at the MMBD7000 and that SOT package would be even worse for me than two 1n4148. No way to solder to it without probably overheating it. Unless I buy a $220 iron and a $50 magnifier lamp. The third leg could short out on the heat sink, too.
In my case two 1n4148 in series wouldn't work because the hole in the heat sink for the stabistor was too short to put it in there. I think manufacturers have stopped making stabistors, or distributors stopped stocking them, because a green LED drops the same voltage forwards. Long lead is plus I believe. If you use a green LED, paint it first as they can pick up light and be variable.
In my case some kind diy expert scrapped a Peavey amp and mailed me one.
I looked at the MMBD7000 and that SOT package would be even worse for me than two 1n4148. No way to solder to it without probably overheating it. Unless I buy a $220 iron and a $50 magnifier lamp. The third leg could short out on the heat sink, too.
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if it wasn't the problem it definitely needs replaced now anyway. I bought 2 of these, both have the same problem. The stabistor was the 2nd burnt component below the silver cap. This is on the control board which is mainly the meters, lights etc
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do know that I sincerely appreciate everyone taking the time to mess with this
The stabistor is CR13
The stabistor is CR13
Yes, you have plenty of room for a green led on that board. Nail polish over it is fine to block any external light and prevent noise. 1.5 v or thereabout voltage drop. yellow led is a little lower in voltage. Newark my main supplier doesn't stock them usually, but I have found them at parts-express and Jameco. Or salvaged them from old blown motor drives (VFD).
The current on the first generation LED's is assumed to be 10 ma, but the newer ones (I got a 110 pack from P-E last month) are designed for 20 ma. If the top of the + feed to the stabistor is 12 v (which the zener diode says, right?) then a 10 k resistor should keep the current totally within limits. If the SCR CR15 and Q8 blow, all bets are off. If that has happend before I'd put a 5 watt zener in for CR1 to try to keep the voltage clamped in failure mode. Make sure R38 is a tenth watt resistor or something to blow up if that happens, instead of your zener + LED/stabistor.
The current on the first generation LED's is assumed to be 10 ma, but the newer ones (I got a 110 pack from P-E last month) are designed for 20 ma. If the top of the + feed to the stabistor is 12 v (which the zener diode says, right?) then a 10 k resistor should keep the current totally within limits. If the SCR CR15 and Q8 blow, all bets are off. If that has happend before I'd put a 5 watt zener in for CR1 to try to keep the voltage clamped in failure mode. Make sure R38 is a tenth watt resistor or something to blow up if that happens, instead of your zener + LED/stabistor.
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so you feel the green led would be better than 2 1n4148's in series - along with your other suggestions ?
I'm sure I can round up a green led out of something lying around here
I'm sure I can round up a green led out of something lying around here
The green LED is neater anyway, without a second solder joint out in the open unsupported. Those little short leads between the two glass bulbs are an invitation to overheat the diodes, also. My solder joints are nothing to brag about - I pulled one loose today modifying a power wire to install a series relay contact. I was going to cut the wire but no need, it pulled right off the switch terminal.
I sincerely appreciate you taking the time with this. I'm putting together a shopping list to recap a HK Citation 17 preamp I just got and once I finish up with that, I'll see if I can't find a green led and take care of that and the other things u mentioned. Once that's taken care of, I'll still need to recap the amp but I'll bring it up on a variac and light bulb current limiter and see if it's working.
I'm sure I'm not the only one you've taken the time to help, just know it is sincerely appreciated. It allows even idiots like me to get our gear going and makes it an affordable "hobby"
I'm sure I'm not the only one you've taken the time to help, just know it is sincerely appreciated. It allows even idiots like me to get our gear going and makes it an affordable "hobby"
The STB-567 stabistor has a forward voltage = 1.46V +-5%.
Another possible choice albeit even more complex, is to use 1x 1N4148 silicon diode + 2x 1N5711 Schottky diodes -all 3 in series to have a total forward voltage of ~1.42V at 1mA at 25oC.
Another possible choice albeit even more complex, is to use 1x 1N4148 silicon diode + 2x 1N5711 Schottky diodes -all 3 in series to have a total forward voltage of ~1.42V at 1mA at 25oC.
I have a precedent 600xl amp that is a parts amp, was actually scooting it out of the way when I noticed it didn't just have red led's in the faceplate, it also had some green ones with nice long legs on it, seems perfect to me.
Curious, instead of clear fingernail polish, could I use clear enamel spray paint ? Same stuff I use to spray the pcb boards when I'm finished.
I'm also working on my car but sometime this morning I plan on installing the board and firing her up using a variac and light bulb dimmer - my fingers crossed of course.
Might be my lucky week so I have high hopes. I just bought a black HK Citation 17 preamp on ebay to use for these amps when done. Seller said it wasn't working, sold it to me for $99 plus shipping. Got it yesterday, after bringing it up on the variac, everything looked ok on the meter so I hooked it up - listening to it now. Is just the red power light isn't working, rest of it's working fine. Ordering all the new caps today.
Curious, instead of clear fingernail polish, could I use clear enamel spray paint ? Same stuff I use to spray the pcb boards when I'm finished.
I'm also working on my car but sometime this morning I plan on installing the board and firing her up using a variac and light bulb dimmer - my fingers crossed of course.
Might be my lucky week so I have high hopes. I just bought a black HK Citation 17 preamp on ebay to use for these amps when done. Seller said it wasn't working, sold it to me for $99 plus shipping. Got it yesterday, after bringing it up on the variac, everything looked ok on the meter so I hooked it up - listening to it now. Is just the red power light isn't working, rest of it's working fine. Ordering all the new caps today.
The idea of the fingernail polish on the LED is to block light from shining on it, so it doesn't cause noise. LED's are photodiodes, also. So clear is the wrong color. Any kind of colored paint would work, even whiteout. I suppose art type oil paint is too transparent, except white.
If you're passionate about the 1.46 v, yellow LED are a little lower in voltage than green. About 1.4 I think, use your diode function to measure if your meter will test LED's. I don't think a tenth off should hurt this circuit.
Great luck on the preamp. They are getting pricey with an RIAA input, $$$$ so I reworked an old $15 Herald disco mixer to sound good. Not enough line level inputs though, I'm still swapping cables some. I'm trying my first ebay electronics buy, $22 for a blown 400 W amp that is 14 lb lighter than my PV-1.3k. Closes tomorrow. So when repaired I can play my keyboard out in public without struggling. I don't need 650 w/ch anyway, I'll never play for more than 80 people. Vendor was 300 miles from me so feight is not prohibitive, as it usually is on anything that big.
If you're passionate about the 1.46 v, yellow LED are a little lower in voltage than green. About 1.4 I think, use your diode function to measure if your meter will test LED's. I don't think a tenth off should hurt this circuit.
Great luck on the preamp. They are getting pricey with an RIAA input, $$$$ so I reworked an old $15 Herald disco mixer to sound good. Not enough line level inputs though, I'm still swapping cables some. I'm trying my first ebay electronics buy, $22 for a blown 400 W amp that is 14 lb lighter than my PV-1.3k. Closes tomorrow. So when repaired I can play my keyboard out in public without struggling. I don't need 650 w/ch anyway, I'll never play for more than 80 people. Vendor was 300 miles from me so feight is not prohibitive, as it usually is on anything that big.
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I did mention I'm an idiot in my 1st post didn't I 🙂 Black enamel paint it is.
As the green is already mounted and yellow would be harder to scrounge up - I'll just stick with the green for now.
Citation 17 - I can't say I'm really that familiar with them, never paid much attention to them, sort of stumbled into this one. Cosmetically it's in really nice shape and while I've always been a fan on vintage silver face gear, I really like the black.
Not sure if I'll get to it soon as I'm planning on moving to Mexico no later than April but the project I look forward to the most is I have a HK Citation II amp that I traded to someone so effectively cost me very little money. Guy I got it from took it to someone to restore for him and like a year later all the guy did was paint it and get new sockets installed, so it's in pieces but it's all there. I'm trying to get the simpler projects done before I go and things are pretty hectic trying to get things ready and it's not a project I want to rush. I'll also have more money to sink into it when I get to Mexico. I either plan on doing a lot of traveling or putting together what would be for me the ultimate stereo ........🙂
As the green is already mounted and yellow would be harder to scrounge up - I'll just stick with the green for now.
Citation 17 - I can't say I'm really that familiar with them, never paid much attention to them, sort of stumbled into this one. Cosmetically it's in really nice shape and while I've always been a fan on vintage silver face gear, I really like the black.
Not sure if I'll get to it soon as I'm planning on moving to Mexico no later than April but the project I look forward to the most is I have a HK Citation II amp that I traded to someone so effectively cost me very little money. Guy I got it from took it to someone to restore for him and like a year later all the guy did was paint it and get new sockets installed, so it's in pieces but it's all there. I'm trying to get the simpler projects done before I go and things are pretty hectic trying to get things ready and it's not a project I want to rush. I'll also have more money to sink into it when I get to Mexico. I either plan on doing a lot of traveling or putting together what would be for me the ultimate stereo ........🙂
Thanks to those who took the time to not just point me in the right direction but pretty much drove me there, it's going to take a while as I have no idea the last time this was turned on so I'm bringing it up SLOWLY but it's all back together and on the variac.
If nothing blows up, I'll recap the driver boards and repeat the process for the 2nd one
Thank you
If nothing blows up, I'll recap the driver boards and repeat the process for the 2nd one
Thank you
Can't thank u enuff. On the variac and l.b. current limiter all day inching up to full power.
Have to leave so shut it down, plugged it into the wall, meter on an output - seemed to be working great. Order is in for the rest of the components, already have the ones to get the other one up and running.
Can't thank everyone enough.
Have to leave so shut it down, plugged it into the wall, meter on an output - seemed to be working great. Order is in for the rest of the components, already have the ones to get the other one up and running.
Can't thank everyone enough.
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