| a_p_deguzman |
hi everyone....
'm just asking if anybody have tried replacing the m250 output transistor. the original output transistor MJ15024/MJ15025. 'm planning to replace the MJ15024/MJ15025 with MJL4281A(NPN)/MJL4302A(PNP). anybody comments and analysis for these particular replacement is it working? or not? thanks just waiting.... see you soooooon.
a_p_deguzman |
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| anatech |
What brand is the M250??
Why not use the originals? They are available, or the TO-3 equiv's. The plastic case does not mount easily where TO-3's were.
-Chris |
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| boraomega |
MJ15024/MJ15025 are Darlingtons, and 4281/4302 are standard bipolars. You can not do that without some other changes in driver stage.
Sorry! My mistake, they are not Darlingtons. :confused: |
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| hienrich |
hi,
if you are referring the attachment,
you are not wrong
the amp will operate happily with those devices you want to replace
with, assuming that there are no PCB layout errors
and also you are close or equal to those assigned biasing voltages.....
:smash: enjoy building you amps.......
rgrds,
macweb |
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| joan2 |
| mj15024/15025 are hermetic to3's what you propose are plastic types, they will work! |
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| hienrich |
some advantages of the MJL4281 and MJL4302's:
higher ft (transistion frequency)
higher hfe, that it can handle more current to load
and a very desirable SOA curve.......
so need not hesitate ;)
rgrds,
macweb |
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| joan2 |
| supply this with +/-35 volts rails and you can use 5pairs of 2n3055/mj2955 trannies which are dirt cheap in our country! 4modules in a bridge will give you more power! |
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| hienrich |
I have tried even +-85vdc with MJL4281's and MJL4302's
at 4ohm loads and forced cooling.......
rgds,
macweb |
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| a_p_deguzman |
thanks hienrich and joan2 for your reply... thanks also hienrich for the schematic with voltage ref... anyway i already have the data sheet of mjl4281/mjl4302.... by the way have you tried mje15034/mje15035 as drivers for mjl4281/mjl4302? these two transistor mje15034/mje15035 rated as 350volts 50watts....
anyway soon ill be starting to build this m250 using these new set of transistors.... whatever problems incountered or outcome ill just post it here....
alan |
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| hienrich |
ap:
for the moment I am using the older MJE15032/33, MJE15030/31
but I love MJE15032/33 which im using right now....
by the way how did you acquire your devices?
happy amping.....
kumusta,
macweb |
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| a_p_deguzman |
hi! hienrich do you have a schematic diagram (m250) with voltage ref. using these two new transistors mjl4281a(npn)/mjl4302a(pnp)? thanks inadvance.... hope to hear you soon....
alan |
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| hienrich |
actually you can still do the same with that scheme I've attached
( by the way let us also thank somebody who originally posted the schemes with biasing voltages, I forgot were that thread that is...)
here, looking to the schemes with the given output devices, you will
have no problems if you directly replace those NPN's with your MJL4281's and those PNP's with your MJL4302's, still
the same voltages appears on those pins designated by the scheme
after it is properly biased.....
here some hint :smash: assuming PCB lay-outs are done correctly
and everything from input differentials to the voltage amp stage
and the driver stage are in place correctly ( never put the output stage yet:att'n: ).
when powering up the boards measure the voltage drop across R22
(75 ohm res) ,mean while turn the trimmer res until you can
measure a voltage drop of about 0.6volts ( positive probe @ point A and the negative probe @ point B)
after which, turn off , then connect now the out put devices....
assuming that all connections are correct ....
turn the power on and quickly, measure the voltage drop across R22 (75ohm res), turn the 1k trimpot until a voltage drop
of about 1 to 1.1 volt across R22 (pos. probe @ A, neg probe @B)
play some music for 15 min. , by this time the heat sinks might
be warmer,
finally measure it again, readjust if it goes high and get it back to 1.1 volts...
or for the most final test there should be a 0.55 Volt drop across each of the Base to Emitter of the output devices.... ( 0.6 volts is a bit high and operate the outputs hotter)
these are just simple biasing when we don't have oscilloscopes...
goodluck,
macweb |
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| anatech |
Hi macweb,
You are further ahead to measure the voltage across the emitter resistors. E-B voltages can vary between transistors types and polarity. The temperature has a great influence also making this measurement unreliable.
-Chris |
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| joan2 |
| quote: | | or for the most final test there should be a 0.55 Volt drop across each of the Base to Emitter of the output devices.... ( 0.6 volts is a bit high and operate the outputs hotter) |
not a good practice!
better measure the quiscient collector current of the output transistors, a range of 150 to 250 ma. assuming 4 pairs output devices will give good result in most cases, cross-over distortion is minimised this way!
base emitter diode measurement is a tricky business! |
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| a_p_deguzman |
hi hienrich kumusta? i don't have any parts yet of the m250 but i already have tried looking and ask for the parts availability here in manila.... i only have gone to one store yet in Alexan here particularly in fairview actually its just one of the braches of alexan.... i only have one problem coz they are out of stock of TIP121 which was used in the dc protection circuit.... mybe this week i have to go the RAON in Quiapo Manila... there have DEECO and ALEXAN main branch.... but i haven't tried yer asking if they have these new transistor MJL4281A & MJL4302A. I also wanted to check the availability of MJE15034 & MJE15035 which will be used as the driver transistors... by the way do have any idea about what transistor will be used as a replacement of TIP121? have you tried these M250 power amp? how does it sound? and have you tried powering higher voltage than the original +-70Vdc?
again thank you very much....
alan |
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| joan2 |
you can get free samples from www.onsemi.com by signing up, registration is free, but nowadays you will have to pay for freight charges! you can get everything you need from there!
buying stuff from raon is risky, lots of fakes going around. stores that carry genuine parts are alexan, oriental, newport, hirose, with deeco you have to be able to spot the originals from the fakes. at times they will ast you if you want originals because the pricing is much different for fakes and originals! |
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| a_p_deguzman |
thanks to joan2 for the info.... so id probably buy in alexan beside DEECO in raon right? how about replacement for the TIP121? do you have any idea what transistor instead of using TIP121?
thanks anyway.... maybe tomorrow ill be checking for the parts availability..... good to hear from you with the info...
alan |
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| hienrich |
:smash:
well, these are only some ways of doing things most specially when
we don't have scopes.....
I have always done this without encountering problems....
Tony: you've also a good point here...
but measuring voltages across devices are more convinient..
and since the ON state of bipolar transistors are approximately from
0.5 volt to 0.65 volt, 0.7 volt is for ideal BJT's....
if you have a working project right now try testing the Base to Emmiter voltages of the output devices (standby state). Assuming they are biased properly....
ap:
for me, I would rather run for (original) Sankens, since they are much
rugged and reliable: 2sc3264(npn), 2sa1295(pnp)
kumusta,
macweb
;) |
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| Tony |
the whole point of knowing your idle currents is to know your output transistor quiscient power dissipation! measuring Vbe alone will not let you find that out!
and it is not hard to do either! what i do is to solder a 10ohm 1watt resistor accross a busted fuse, this i plug into the fuse clips so that when i power up the amp i will know the current by measuring the voltage accross the resistor as i turn the bias pots! i do this on both the +/- rails.
a second benefit from this is in case there is a mistake in the wiring somewhere, the resistors will burn first rather that the output transistors getting fried!
so you see, there are reasons why we do things! |
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| a_p_deguzman |
hienrich kumusta? these sanken transistor you have mention ive been using these about ten years ago with my 150w amp which was taken acctually in the electronics digest... the output stage was using (2sa1216a & 2sc2922a) or (2sa1215a & 2sc2921a) they only differ in Vce. its input stage was using an op amp LM301AN... the low power supply requirement of the op amp was scaled down with the use of limiting resistors and further regulated by zener diodes.....
musta bay?
alan |
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| hienrich |
well, we still have differences in doing things but arrive on the same
place.
many service manuals of knowned manufacturers, places test points
on there service schematics and even voltage drops across these test points
meaning, you place your test probes on those points and measure
those assigned voltages when ever doing a servicing... :)
when doing it your way it is safe but you should also know the
current consumptions of the input and the voltage amplfier stages,
and add them up together with the output stages so you have your
total current consumption....
but what if there is this someone who knows not more on current
consumptions, without scopes and only done his projects by a given schematic and a PCB layout but without construction manuals.....??
so still VBE measurements are essential no matter which bipolar
are used....
rgds,
macweb |
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| anatech |
Hi macweb,
No. What you are doing is incorrect. Period. And another period!:smash:
What is important to know is the actual current through each device, so your idea is correct. Your method is totally wrong.
How do I know? I've serviced gear for over 25 yrs. Warranty for many brands and LARGE power amps. The only accepted method (where emitter resistors exist) is to measure and monitor the voltages (in mV) across the emitter resistors. You want to know the outputs are sharing current equally. You pick an average one and set your bias current from that. End of story.
Now, some manufacturers want you to replace a fuse with a resistor and measure the voltage across that. Others (like Fosgate car amps) want you to look for crossover distortion under load, normally something like 20KHz across 4R at low power. I guess you could use a current probe but that's a bit out there for normal techs.
-Chris |
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| Tony |
my first solidstate amp was a pioneer 707 clone! it was a quasi-complimentary design with bootstrap capacitor and a single 38volt rail,
then a complimentary amp with 2n3055/mj2955 in the late or early 80's with a supply voltage of +/-32volts.
i built my first leach super amp around 1984 using japanese transistors and scaled down psu rails of around +/-60volts dc!
with all the years of experience behind me, repairing power amps like soundcraftsmen, GAS, hafler, and many others of japanese make, i think i am qualified to comment about testing methods!
i can spot where something is amiss!
the m250 is typical design topology that is open for a lot of possible modifications. |
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| Evileagle |
| Does anybody think this amp would survive with +/-75v rails? This amp is going to be my next project and a 110vct toroid would be much more easy to get. |
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| Tony |
| not if you don't change the transistors from the schematics! |
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| Evileagle |
| Which do you recommend to replace them with? I would like to stick with TO-3's because of the heatsinks I have. Finding an 80vct toroid for the originals will be easier than sourcing different heatsinks for plastic devices. :scratch: |
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| Evileagle |
| ok, just realized your were reffering to the other transistors in the circuit rather than the output stage. Which in particular would I need to swap for higher voltage ones? |
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| Tony |
| everything except the protection transistors, and bias setting transistor need to be replaced with a higher Vceo rating, at least 250 volts DC. |
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| Tony |
| quote: | | how about replacement for the TIP121? do you have any idea what transistor instead of using TIP121? |
mje270 is a good replacement, comes in to-77. |
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| ldanto |
heinrich, whoever you are. are you the designer of the M250 at Makus M250
can you update the site or something? i really like the m250 and the mcd 1 and i really want the schematics for the mcd 1 |
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| Evileagle |
| marcus66 is the designer of the M250. |
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| bigpanda |
I happen to have a handful of MJ15003, MJ15004. Can they be use here? What other changes have to be made when using 03/04.
Thanks for tip |
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| Tony |
| quote: | Originally posted by bigpanda
I happen to have a handful of MJ15003, MJ15004. Can they be use here? What other changes have to be made when using 03/04.
Thanks for tip |
i can not see why not! you can use them up to rails of +/-55volts, 4pairs is good. |
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| bigpanda |
Do I need to make any other change to use them?
Just straight substitution ? |
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| jaycee |
| They should just drop straight in. They are slower in fT so there should be no stability problems. If you're running it heavy you might want to use 6 transistors per side instead of 4, but that's about it. You could always drop the rail voltages a little to say 50V or 42V if you want to stick with 4 pairs. |
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| clovi_kate |
hi to all..
with regards to M250.. can i replace the output transistors with 2SA1302(pnp) and 2SC3281(npn)..and also the driver for C2344(npn) and A1011(pnp)..
tnx a lot...
ryan jan:) |
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| Tony |
| quote: | Originally posted by clovi_kate
hi to all..
with regards to M250.. can i replace the output transistors with 2SA1302(pnp) and 2SC3281(npn)..and also the driver for C2344(npn) and A1011(pnp)..
tnx a lot...
ryan jan:) |
if you have them, use them, just beware of fakes!
:D |
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| djk |
" If you're running it heavy you might want to use 6 transistors per side instead of 4, but that's about it. You could always drop the rail voltages a little to say 50V or 42V if you want to stick with 4 pairs."
If they are real, four pair MJ15003/04 will have 2KW SOA at 50V. With ±55V, a 38-0-38 1KVA transformer, and good heatsinking, they will do 500W into 2 ohms. |
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