howdy all, i have fixed my amp with transistors that are somewhat identical, a little bit higher specs but the new transistors are heating up. the amp works and doesnt get into thermal protection.
its a 4channel amp im bridging the fixed channels on a sub as test.
original faulty transistors are b1588 and d2439
replaced with a1941 and c5198
works well, just heats up.. keeps getting hot.. i had it run for over 1.5hrs no thermal protection and no audio issues....
the only thing that i found out that i think could be the issue is the transistor's transition frequency differs.. the old ones work at 55mhz the new ones 30mhz.. can this be the issue of heating up?? does it matter? or can it be somthing else?? what should i check?
thanks!!
its a 4channel amp im bridging the fixed channels on a sub as test.
original faulty transistors are b1588 and d2439
replaced with a1941 and c5198
works well, just heats up.. keeps getting hot.. i had it run for over 1.5hrs no thermal protection and no audio issues....
the only thing that i found out that i think could be the issue is the transistor's transition frequency differs.. the old ones work at 55mhz the new ones 30mhz.. can this be the issue of heating up?? does it matter? or can it be somthing else?? what should i check?
thanks!!
i know ideally they should be from similar manufacture and of same batch, beggers cant be choosey, thats what was available, if its the issue ill change the original ones to the same as what available.. or will i then have 4 heating transistors?
The replacement transistor you used is not a good match/sub.
The original one is a darlington type.
The original one is a darlington type.
The darlington is essentially two transistors in series. They make it easier for the drive circuit to drive the output transistors but require twice the bias voltage. The bias circuit is causing too much idle current. Simply reducing the biasing isn't generally an option because the drive circuit is too weak to drive the non-darlington transistor into a load.
But the drivers arent heating up at all, so your saying my replaced non darlington transistors are drawing max amp all the time? Their always working at max all the time?
How can i tell a darlington trans from a non darlington one?
I guess i must find a better suited darlington pair or ill have 4 trans building heat since its the driver circuit designed for a higher biasing threshhold of the darlingtons, am i understanding this correctly?
Meanwhile will these transies cook themselves? Or just run max heat all the time?
How can i tell a darlington trans from a non darlington one?
I guess i must find a better suited darlington pair or ill have 4 trans building heat since its the driver circuit designed for a higher biasing threshhold of the darlingtons, am i understanding this correctly?
Meanwhile will these transies cook themselves? Or just run max heat all the time?
The non-d transistors aren't working hard but they are dissipating more heat due to incorrect biasing.
The drivers aren't working hard. They work harder at higher output levels and with lower impedance loads.
The non-d outputs may work to some degree but when asked to drive speakers at full power, they could stress the drivers to failure and may not be able to drive to full power without significant distortion.
The added heating from excessive biasing will make the transistors more likely to fail due to higher operating temperatures.
The drivers aren't working hard. They work harder at higher output levels and with lower impedance loads.
The non-d outputs may work to some degree but when asked to drive speakers at full power, they could stress the drivers to failure and may not be able to drive to full power without significant distortion.
The added heating from excessive biasing will make the transistors more likely to fail due to higher operating temperatures.
Ok i have found d2439 localy, but somhow they have b1587 not b1588... is it okay? The difference is handling 8amps instead of 10amps... is it ok or should i search further?
Less reliable is okay only IF i cant find any 1588s
Yes I checked the link, thanks, i wish i can find locally. Wish there was anything as a substitute but seems not need to find 1588.
If worst comes to worst can i replace this channel only with 1587 along with a 2438 those complement each other at 8amps vs 10amps of the others...
If they blow themselves out id be happy as long as they dont cause any other faults like taking out the drivers or the chip with them...
If i find 1255s complementary to 1895 would these put any strain on the drivers or anything? These would be slightly more powerful at 12amps and 100watts...
Can i not change anything on the second channel?
This is what i need:
2SB1588 datasheet(1/1 Pages) SANKEN | Silicon PNP Epitaxial Planar Transistor(Audio, Series Regulator and General Purpose)
this is whats available:
2SB1587 datasheet(1/1 Pages) SANKEN | Silicon PNP Epitaxial Planar Transistor(Audio, Series Regulator and General Purpose)
This is what i hope to find if what i need isnt available:
2SB1255 datasheet(1/3 Pages) PANASONIC | Silicon PNP epitaxial planar type Darlington(For power amplification)
2SB1588 datasheet(1/1 Pages) SANKEN | Silicon PNP Epitaxial Planar Transistor(Audio, Series Regulator and General Purpose)
this is whats available:
2SB1587 datasheet(1/1 Pages) SANKEN | Silicon PNP Epitaxial Planar Transistor(Audio, Series Regulator and General Purpose)
This is what i hope to find if what i need isnt available:
2SB1255 datasheet(1/3 Pages) PANASONIC | Silicon PNP epitaxial planar type Darlington(For power amplification)
Lets just say for educational and informational purposes, when one doesnt find what he needs what are the pros and cons of substituting with a closely lesser spec or closely higher spec component what are my consequences? All the above handle 160V the lesser two are 80w designed for 60-70watt/channel amps, the 1255 handles 100w and designed for 90watt/channel amps.. my main difference is amperage handling, 8a vs 10a (originally used) and 12a
Would the 1255 require more voltage to open and close its circuit? Needing higher gain setting? And the lesser component's channel will reach distortion before the other 3 channels?
Would the 1255 require more voltage to open and close its circuit? Needing higher gain setting? And the lesser component's channel will reach distortion before the other 3 channels?
You can't use only a few specs/parameters to determine if a substitute will work.
Examples...
When an amp is designed by an engineer, they have ti use capacitors and other components to make sure that the amp behaves (no undesired oscillation under varying loads, etc). Different transistors may require different values of damping components to stabilize the circuit.
When the bias circuit is set up (by the design engineer), it's meant to compensate for temperature based on the various temperature vs threshold characteristics of the transistors in the circuit. Any substitute could make the bias unstable resulting in distortion at some temperatures and bias avalanche at other temperatures.
Examples...
When an amp is designed by an engineer, they have ti use capacitors and other components to make sure that the amp behaves (no undesired oscillation under varying loads, etc). Different transistors may require different values of damping components to stabilize the circuit.
When the bias circuit is set up (by the design engineer), it's meant to compensate for temperature based on the various temperature vs threshold characteristics of the transistors in the circuit. Any substitute could make the bias unstable resulting in distortion at some temperatures and bias avalanche at other temperatures.
Thank you Perry very much for such thorough clear complete and educational answers, indeed its more complicated than black and white, i will wait to find the proper required transistor. I just was hoping the 1587 would have been a better temporary fix than the non-darligton pair that i used. No point in refixing twice, im holding off to find/get the required parts.
Found proper replacements, removed previously installed non-darlington transistors, installed the proper darlington ones and bump tested the amp.... 2ohm bridged.... was expecting overcurrent draw protection or overheat protection when the amp went silent... turned down volume nothing came back turned remote off and on, nothing came back...
Long story short, burned out the replaced darlingtons, got another pair and installed and its working now.
I dont get it.. i do understand this amp is not 1ohm stable stereo, 2ohm bridged, but i dont understand how the protection circuit did not kick in! Hell it did kick in with the non-darlington transistors!! I am testing it by pushing it to the limit without clipping! With the non-darlingtons sure it ran hot as hell but overcurrent protection did kick in and when i turned down the volume the amp turned back on...
So am i supposed to replace the paired channel? That way they are equally lesser capability than the original factory ones? That way the load is equally split? Tomorrow i plan on running it full tilt with 4ohm load and see if its gonna handle 1-1.5 hr drive.
The load is two dual 4ohm 12s wired to 4ohm.. im guessing its a bit less than 4ohm so it would be a good test. Im just puzzled why the amp originally burned out and now again burned out without protecting itself...
If i replaced both left and right transistors of channel B would i end up with 4 burnt transistors? Or overcurrent protection?
Long story short, burned out the replaced darlingtons, got another pair and installed and its working now.
I dont get it.. i do understand this amp is not 1ohm stable stereo, 2ohm bridged, but i dont understand how the protection circuit did not kick in! Hell it did kick in with the non-darlington transistors!! I am testing it by pushing it to the limit without clipping! With the non-darlingtons sure it ran hot as hell but overcurrent protection did kick in and when i turned down the volume the amp turned back on...
So am i supposed to replace the paired channel? That way they are equally lesser capability than the original factory ones? That way the load is equally split? Tomorrow i plan on running it full tilt with 4ohm load and see if its gonna handle 1-1.5 hr drive.
The load is two dual 4ohm 12s wired to 4ohm.. im guessing its a bit less than 4ohm so it would be a good test. Im just puzzled why the amp originally burned out and now again burned out without protecting itself...
If i replaced both left and right transistors of channel B would i end up with 4 burnt transistors? Or overcurrent protection?
For the record i bought the amp used and burnt and planned on fixing it. I figured somthing crazy had happened to it to get burnt in the first place... the previous owner said he had 4 oval speakers on one channel (2ohm stereo) and a single 4ohm sub on other channel.. so its 100% within its designed working order.. i assumed some tweeters were burned/shorted or somthing to cause the amp to fail...
I know its a 4 channel amp, just so happens that pioneer has mentioned on the side channel A and channel B referring to front channels as one and rear channels as one.. weird..
I know its a 4 channel amp, just so happens that pioneer has mentioned on the side channel A and channel B referring to front channels as one and rear channels as one.. weird..
The non-darlington transistors are likely rated for higher current which would explai why they survived.
The amp is designed to drive 2 ohm stereo, 4 ohm mono, minimum.
The amp is designed to drive 2 ohm stereo, 4 ohm mono, minimum.
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