Hi!
I have an old (1976) Japanese made amplifier from Eagle International. One of the power stages and driver stages are blown.
The following transisitors are broke.
2x C789.
1x C853. (driver)
1x A545. (driver)
The C853 and A545 are complementary!
If i'm correct, the most common replacement fot the C789 is the BD243C
I don't know the replacement's for the C853 and A545. I do have some specs:
2SC853. SI-N 70volts 0.2A 0.4W NPN
2SA545. SI-N 70volts 0.2A 0.4W PNP
Who has the replacments for me?
Besides this problem I have another question.
Why isn't there a NPN and PNP transistor used in the power stage? I found it strange beqause the drivers were NPN and PNP. Is this common for these amplifiers?
Thanx!
I have an old (1976) Japanese made amplifier from Eagle International. One of the power stages and driver stages are blown.
The following transisitors are broke.
2x C789.
1x C853. (driver)
1x A545. (driver)
The C853 and A545 are complementary!
If i'm correct, the most common replacement fot the C789 is the BD243C
I don't know the replacement's for the C853 and A545. I do have some specs:
2SC853. SI-N 70volts 0.2A 0.4W NPN
2SA545. SI-N 70volts 0.2A 0.4W PNP
Who has the replacments for me?
Besides this problem I have another question.
Why isn't there a NPN and PNP transistor used in the power stage? I found it strange beqause the drivers were NPN and PNP. Is this common for these amplifiers?
Thanx!
When this was designed there were no PNP power silicon transistors available for sensible money. So they used what is called a quasi complementary output, where the drivers are complementary and the powers were both NPN. I would probably use BC139 (PNP) and BC140 (NPN) to replace the drivers. Watch the pinouts as they are not the same.
Tony
Tony
In those days, power PNP transistors were rare, expensive, and not very good... so they used an output stage type called quasi-complimentary.
2SC789 seems to be a TO-220 package. The recommended BD243C would work well here.
As for the drivers, BD139/140 should work well. They are not as fast as the originals, but they should work well.
2SC789 seems to be a TO-220 package. The recommended BD243C would work well here.
As for the drivers, BD139/140 should work well. They are not as fast as the originals, but they should work well.
Hi Tony,
The Collector voltage is higher in this amplifier, 56 volts on the 2SC853. The ones you named only go to 40 volts. Also is the BC119 complementary to the BC139 and not the BC140.
As I was saying to Tony, the Collector voltage is not high enough. Following the sheets it say's that they are not complementary to each other, is that not a problem then?
I really don't know if this is possible.....Is it possible to change the output driver to an NPN and a PNP driverpair? 😕
EDIT: Sorry, you were saying BD and Tony BC types. So with the BD139/140 types it will work right?
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hello.
my quick reference list shows this:
bd 243c is the substitute for 2sc789
and bc639/bc640 are for 2sc853/2sa545
greets
my quick reference list shows this:
bd 243c is the substitute for 2sc789
and bc639/bc640 are for 2sc853/2sa545
greets
BD243C has VCEO of 100V versus the 2SC789's 70V and should be adequate.
The BD139/140 have VCEO of 80V which is adequate also. Also the BD139/140 package should fit well in the original pinout. BC639/640 would work for drivers too but you might need to fix some heatsinks to these small TO-92 packages.
Another thought - you might want to replace both channels even if the other is working. It would be better if they matched.
The BD139/140 have VCEO of 80V which is adequate also. Also the BD139/140 package should fit well in the original pinout. BC639/640 would work for drivers too but you might need to fix some heatsinks to these small TO-92 packages.
Another thought - you might want to replace both channels even if the other is working. It would be better if they matched.
And remember to power up with a light bulb in series with the mains (60 to 100 watt) first, to avoid any problems if there should be any other fault on the amp. It can save blowing the outputs again.
When it's all fixed, check and reset the output bias.
When it's all fixed, check and reset the output bias.
ALSO KEEP IM MIND ....that an other output setup might require or draw other idle ...it is quiet common for these amplifier not to feature an idle trimmer ...in this case you might loose the all set up if not careful
the best way is if a trimmer exist to tune it for as lower bias is possible ( verify that more than once in some amps trimers work CW or CCW depenting on the location )
then again if no trimmer exist and bias is coming to the vbe with a fixed resistor it will be nice to find how and where and apply a trimmer so bias is no longer fixed but adjustable ...
that will save you from a lot of trouble
the best way is if a trimmer exist to tune it for as lower bias is possible ( verify that more than once in some amps trimers work CW or CCW depenting on the location )
then again if no trimmer exist and bias is coming to the vbe with a fixed resistor it will be nice to find how and where and apply a trimmer so bias is no longer fixed but adjustable ...
that will save you from a lot of trouble
The amplifier works like a champ!
I don't have a light for the mains so i double checked everything. No problems were there. I will make something like that, seems handy 😉
Is it possible that with the new transistors in place the distortion is lower?
I can really hear a difference between the two channels. The old channel seems to put more mid frequenties in place when played at higher volumes. The channel with the new transitors in it sounds more quiet, less agressive.
I measured some hFe's on the old transistors on the other channel but the're al fine.
I'm going to replace the transistors on the other channel to but I'm waiting for Some BD243C's. They were out of stock at the electronics shop.
The amplifier uses output capacitors so I don't know how to change the idle bias.
There is only one trim for each channel. It's located between the main ground and the base of a 2sa545 transistor wich is even before the onces that drive the output transistors wich were broke.
What does this trim do?
On both sides i measured 996mV on the base of that transisitor so that looks fine to me beqause both channels were having the same value.
I'm a hobby electrician so I don't know anything so please correct me if I am wrong at some place!
Thanx
I don't have a light for the mains so i double checked everything. No problems were there. I will make something like that, seems handy 😉
Is it possible that with the new transistors in place the distortion is lower?
I can really hear a difference between the two channels. The old channel seems to put more mid frequenties in place when played at higher volumes. The channel with the new transitors in it sounds more quiet, less agressive.
I measured some hFe's on the old transistors on the other channel but the're al fine.
I'm going to replace the transistors on the other channel to but I'm waiting for Some BD243C's. They were out of stock at the electronics shop.
The amplifier uses output capacitors so I don't know how to change the idle bias.
There is only one trim for each channel. It's located between the main ground and the base of a 2sa545 transistor wich is even before the onces that drive the output transistors wich were broke.
What does this trim do?
On both sides i measured 996mV on the base of that transisitor so that looks fine to me beqause both channels were having the same value.
I'm a hobby electrician so I don't know anything so please correct me if I am wrong at some place!
Thanx
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The transistors can alter distortion... but we are talking theoretically and about pushing the boundaries of what can be achieved in a design (such as a sub 0.01% design)
In the Eagle, it's not going to make any difference.
On an AC coupled amp there are often two adjustments... and yours seems to have just one, which from your description will be to set the "mid point" voltage at the outputs.
You measure the supply voltage the output stage runs on (say 60 volts) and then measure the DC voltage at the "output" of the amp, which will be one end of the speaker coupling capacitor. You adjust that point to be half the supply (so that's 30 volts). Doing that enables the amp to give maximum output before clipping.
The missing adjustment is quiescent current. Thats a small constant current that flows in the outputs to minimise crossover distortion and would be around 50 milliamps at a guess. If there is no other pot then it's a fixed bias scheme.
If you genuinely believe there is a difference in sound between the two channels... then the only surefire way is to measure and use a 'scope. If you haven't got that, then the best you can do is to make sure you use the same spaeaker and the same input on both channels. It's so easy to imagine differences sometimes 🙂
Replacing ANY or all of the transistors has zero effect on the apparent "loudness" or gain of the amp. That is determined by such things as negative feedback, which removes the transistor "hfe" and other parameters from the equation.
In the Eagle, it's not going to make any difference.
On an AC coupled amp there are often two adjustments... and yours seems to have just one, which from your description will be to set the "mid point" voltage at the outputs.
You measure the supply voltage the output stage runs on (say 60 volts) and then measure the DC voltage at the "output" of the amp, which will be one end of the speaker coupling capacitor. You adjust that point to be half the supply (so that's 30 volts). Doing that enables the amp to give maximum output before clipping.
The missing adjustment is quiescent current. Thats a small constant current that flows in the outputs to minimise crossover distortion and would be around 50 milliamps at a guess. If there is no other pot then it's a fixed bias scheme.
If you genuinely believe there is a difference in sound between the two channels... then the only surefire way is to measure and use a 'scope. If you haven't got that, then the best you can do is to make sure you use the same spaeaker and the same input on both channels. It's so easy to imagine differences sometimes 🙂
Replacing ANY or all of the transistors has zero effect on the apparent "loudness" or gain of the amp. That is determined by such things as negative feedback, which removes the transistor "hfe" and other parameters from the equation.
The technical specs of this eagle A2004 are not that bad for such a cheap amplifier.
In fact were these the luxury line of Eagle international.
I also have the T2008 tuner and I have read a test that these components were very good value for the money!
It even delivered more power then the specificationson paper. 26w @ 8 ohms and 36watt @ 4ohms
20watt per channel @ 8 ohms.
30watt per channel @ 4 ohms.
Frequency responce: 15Hz-36Khz +/-2dB
Power bandwith: 13Hz-50Khz +/- 3dB
Maximum Harmonical distortion: 0.2%
Damping Factor: 35 @ 8 ohm
S/N Phono: Better than 68dB
S/N Aux, tuner, tape:better than 80dB
I compared the trimms with another old manuel from a Teleton amplifier and they are indeed for the center voltage. The main power supply was 56.2 volts so devided with two it makes 28.1 volts. I changed both channels to 28.00/28.01 volts.
I don't have a scope but i have good ears! I will compare the channels again when the other channel is also changed.
The only thing that's left is that the unmodified channel sometimes makes a ssss sound for one second. So it's quiet and then ssss and it's quiet again. Whats that?
In fact were these the luxury line of Eagle international.
I also have the T2008 tuner and I have read a test that these components were very good value for the money!
It even delivered more power then the specificationson paper. 26w @ 8 ohms and 36watt @ 4ohms
20watt per channel @ 8 ohms.
30watt per channel @ 4 ohms.
Frequency responce: 15Hz-36Khz +/-2dB
Power bandwith: 13Hz-50Khz +/- 3dB
Maximum Harmonical distortion: 0.2%
Damping Factor: 35 @ 8 ohm
S/N Phono: Better than 68dB
S/N Aux, tuner, tape:better than 80dB
I compared the trimms with another old manuel from a Teleton amplifier and they are indeed for the center voltage. The main power supply was 56.2 volts so devided with two it makes 28.1 volts. I changed both channels to 28.00/28.01 volts.
I don't have a scope but i have good ears! I will compare the channels again when the other channel is also changed.
The only thing that's left is that the unmodified channel sometimes makes a ssss sound for one second. So it's quiet and then ssss and it's quiet again. Whats that?
I dunno 😉 What's what ?
More info required... Does the noise depend on the setting of the volume control ? Does it do it on any input ? Does it do from cold and continue doing it ?
Does it respond to physically tapping the PCB (poor joint somewhere). That trimmer that sets the mid point might be noisey... try (with it off) turning it a dozen time or so then reset it.
It might be a faulty component like a capacitor... tantalums and ceramics and suflex types are the suspects.
And talking of caps, all the electroylitics would benefit from being replaced, or should I say the amp would benefit from having them all replaced 🙂
Loud and clear!
I will look at the capacitors. I was planning to replace all the electroylitics anyway beqause of the age of this amp. I know it is used very often, I'm the second owner. But I will look at the ceramic capacitors to. Maybe I'm going to replace the trimms aswell, it could not harm the amp.
I just found out that the amp even has an RIAA correction in the phono stage, all in a cheap amp! I found 2capacitors for each channel, 47pF and 470pF. I'm going to replace those with something better. Ceramics in a riaa correction......
Even all the pots for volume, bass treble are from Alps. Thats a good thing to.
And for the people who want to know wich amp it is...
http://www.mijnalbum.nl/GroteFoto-U68YPU4O.jpg
I will look at the capacitors. I was planning to replace all the electroylitics anyway beqause of the age of this amp. I know it is used very often, I'm the second owner. But I will look at the ceramic capacitors to. Maybe I'm going to replace the trimms aswell, it could not harm the amp.
I just found out that the amp even has an RIAA correction in the phono stage, all in a cheap amp! I found 2capacitors for each channel, 47pF and 470pF. I'm going to replace those with something better. Ceramics in a riaa correction......
Even all the pots for volume, bass treble are from Alps. Thats a good thing to.
And for the people who want to know wich amp it is...
http://www.mijnalbum.nl/GroteFoto-U68YPU4O.jpg
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