Hey guys I have an older no name brand PA amplifier and was wondering if anyone could tell me approximately how many watts its capable of? It has a 1,000va toridial transformer with +/- 51v for the 2 amps, I measured 71.9vdc at the amp modules. The amps have 3 pairs of transistors in the output section and are 2sd2837s and 2sd1186s. Let me know if there's any other info needed and I'll try my best to figure that out. Thanks
I forgot to mention that by the power cord input it says 120v 8a and the rectifier diode inside is rated for 600v 8a
I forgot to mention that by the power cord input it says 120v 8a and the rectifier diode inside is rated for 600v 8a
Goven the supply voltage.
P = (Usupply/1.5)^2 V/ 8 ohms.
For 70 volts that would be ((70/1.5)^2)/8 = 275 Watts @ 8 ohms.
That also matches with the power transformer rating.
However it does not match with the transistor types.
I can't find the datasheet foor 2SD2837.
And 2SA1186 is a 50W switching transistor which does way too high Vceo rating and way too low a power rating.
P = (Usupply/1.5)^2 V/ 8 ohms.
For 70 volts that would be ((70/1.5)^2)/8 = 275 Watts @ 8 ohms.
That also matches with the power transformer rating.
However it does not match with the transistor types.
I can't find the datasheet foor 2SD2837.
And 2SA1186 is a 50W switching transistor which does way too high Vceo rating and way too low a power rating.
Type Designator: 2SA1186
Material of Transistor: Si
Polarity: PNP
Maximum Collector Power Dissipation (Pc): 100 W
Maximum Collector-Base Voltage |Vcb|: 150 V
Maximum Collector-Emitter Voltage |Vce|: 150 V
Maximum Emitter-Base Voltage |Veb|: 5 V
Maximum Collector Current |Ic max|: 10 A
Max. Operating Junction Temperature (Tj): 150 °C
Transition Frequency (ft): 60 MHz
Collector Capacitance (Cc): 110 pF
Forward Current Transfer Ratio (hFE), MIN: 50
100W, three parallel, could work.
Jan
Material of Transistor: Si
Polarity: PNP
Maximum Collector Power Dissipation (Pc): 100 W
Maximum Collector-Base Voltage |Vcb|: 150 V
Maximum Collector-Emitter Voltage |Vce|: 150 V
Maximum Emitter-Base Voltage |Veb|: 5 V
Maximum Collector Current |Ic max|: 10 A
Max. Operating Junction Temperature (Tj): 150 °C
Transition Frequency (ft): 60 MHz
Collector Capacitance (Cc): 110 pF
Forward Current Transfer Ratio (hFE), MIN: 50
100W, three parallel, could work.
Jan
https://alltransistors.com/transistor.php?transistor=7015
Can't find anything on the 2837 but found this thread on here from 2009 where a guy was working on an amp with the same transistors.
https://www.diyaudio.com/community/threads/replacement-for-sanken-a1186-c2837.148355/
Can't find anything on the 2837 but found this thread on here from 2009 where a guy was working on an amp with the same transistors.
https://www.diyaudio.com/community/threads/replacement-for-sanken-a1186-c2837.148355/
Scary part is it says on the back that it's 2ohm stereo minimum and 4ohm bridged. 😬 I've tried it with some 8ohm and 4ohm speakers so far and it sounds pretty good. Better than I expected! Also tried it with a 4ohm passive 8" subwoofer I built and it worked well but too much power for it. I have a pair of electrovoice eliminators with 15" woofers that I haven't tried yet. They're 8ohms each I might try bridging the amp and trying them out see what happens.
2 ohm will be risky, on edge of failure. It will likely work for a while, but not last. Keep it a 4 ohm.
If looking for transistor replacement use whatever Sanken “LAPT” pair is in production. Or OnSemi 3281/1302 (go straight to the bigger ones for PA use).
If looking for transistor replacement use whatever Sanken “LAPT” pair is in production. Or OnSemi 3281/1302 (go straight to the bigger ones for PA use).
Thanks for all the quick replies everyone. I will definitely stick to 4ohm or 8ohm. When I saw it said 2ohm min I thought that sounded strange and didn't plan on trying that.
In my answer I quoted incorrectly the type 2SA1186 instead of 2SD1186.
The OP specified 2SD1186
My spec for 2SD1186 was correct. And thus questionable for this application
Yes you are right, that 2SD1186 wouldn't cut it.
Perhaps the OP really meant 2SA1186.
He said: '2sd2837s and 2sd1186' and it is clear that one or the other is incorrect as they should be complementary.
Maybe he can verify?
Jan
Perhaps the OP really meant 2SA1186.
He said: '2sd2837s and 2sd1186' and it is clear that one or the other is incorrect as they should be complementary.
Maybe he can verify?
Jan
Nice find.. That indeed is a complementary pair. Accuracy is a first demand when assessing transistors.
I don't think I would connect 2 ohms to a class AB stage supplied with 70V and 3 transistors rated for 10A. And 150V Vceo is darn close for 72V unloaded supply voltage. One spike which drives one transistor into saturation and you have 144V from the capacitors on the other half of the output stage.
Not to mention the amplifier might have been connected to 110V mains during measuring. Tolerance on mains voltage is +/- 10%.
Sorry I took the cover back off which is a lot of screws and the transistors are Sankens marked c2837 and a1186. So you guys were right I wrote the wrong prefix down when typing my original post. I was looking online last night and saw a LJM L12-2 amplifier board that uses the same transistors.
Yes that's what I did but I dont trust myself to not turn it up too much and blow my subwoofer. I need a larger subwoofer to keep up with my speakers so I'm tempted to turn it up a little too much.
Unless you have a 500W+ amp, it's extremely unlikely that you blow up a sub with too much sound.
Jan
Jan
Kind of NOT derated (150V-10A part).
Those old Sanken A1186/C2837's are obsolete (80's) , $hit for SOA @ 70V. Even 3 pairs is ridiculous for that voltage.
Sanken replaced them with A1386/C3519 - these are 88' to present. 20% better SOA/160V/15A.
Even these in my Sonance 260 (true SOA bridgeable) , they only run at +/- 47V rails - where SOA is far greater.
71V is where the Wolverine builders use 4 pair TO-264 250V parts (ON semi). Those amps are only rated 200W/8R - 350/ 4R.
Yikes !!
For comparison , I run 2 pair A1386/C3519's in my Sonance = 70W/150W +/- 47V rails.
I run 3 pair in my "little" Wolverine , 150W/250W +/- 60V rails.
I've only seen a "true" long term tested 400W on a 4 pair MT-200 - 2SA1216/2SC2922 output stage @ 70V rails.
If you are seeing A1186/C2837 for sale or included in kits - FAKE.
OS
Well transformer wise it is basically 1000va or 1000 watts
So that is the current limit. Once it wants more current for 4 ohm and 2 ohm loads
It doesn't have it, so rail voltage will sag.
rather typical for many pa amps of this size with 800 to 1000 va transformers.
The power is limited to the transformer size. So max current for output transistors is limited as well.
Class AB amplifier and AC output wont fully swing to the rails of course.
So overall efficiency wont utilize much more than 500 watts of that 1000 watt transformer.
Pretty basic stuff. You cant get more than about 250 watts maybe 275 watts per channel.
Depending on how much the rail voltage starts to sag under load.
So assuming a typical average to good pa amp would just likely toss in forced air cooling or fans above
200 watts.
Agree it is marginal, but like any power amp if its hot and you short it. Dont expect magic regardless
DC protection relay is your friend on the output. Which should be mandatory or otherwise standard
for any amp with transformers over 300va
So that is the current limit. Once it wants more current for 4 ohm and 2 ohm loads
It doesn't have it, so rail voltage will sag.
rather typical for many pa amps of this size with 800 to 1000 va transformers.
The power is limited to the transformer size. So max current for output transistors is limited as well.
Class AB amplifier and AC output wont fully swing to the rails of course.
So overall efficiency wont utilize much more than 500 watts of that 1000 watt transformer.
Pretty basic stuff. You cant get more than about 250 watts maybe 275 watts per channel.
Depending on how much the rail voltage starts to sag under load.
So assuming a typical average to good pa amp would just likely toss in forced air cooling or fans above
200 watts.
Agree it is marginal, but like any power amp if its hot and you short it. Dont expect magic regardless
DC protection relay is your friend on the output. Which should be mandatory or otherwise standard
for any amp with transformers over 300va