Ok, no bridge, then no way even on 4ohms to get 150W with 35V rails that WILL sag.
Then this 300W number is a total lie. Vaporware!
Not really, if you didn't push it too hard to kill it, then it's fine, but there is no way you ever got, or will, get 300W from it on 4ohms.
Lucky you didn't load it hard.
Well, if you know it to be 4ohms, that's fine, but you may not know how much power you are truly sending it with that amp.
It's simple, 300W (rms) on 4ohms, is almost 35V RMS, which is almost 49V peak. Obviously that amp hasn't got nearly enough rail voltage to produce that level of swing.
It's just the reality. The numbers you were sold on were just fake.
And, with a Vce Rating of 60V for those MJ2955/3055s, they have a tough job at ±35Vdc, even with no load.
I have some experience with the EQUA amplifier, an Elektor design of 1970. I built lots of them, because they sounded fine for a DIY amp of those days. But, despite VI protection, the outputs used to fail even at shortest overloads, and also with no load when supplied from a 50Vac secondary with bridge and 10mF smoothing cap.
Best regards!
I have some experience with the EQUA amplifier, an Elektor design of 1970. I built lots of them, because they sounded fine for a DIY amp of those days. But, despite VI protection, the outputs used to fail even at shortest overloads, and also with no load when supplied from a 50Vac secondary with bridge and 10mF smoothing cap.
Best regards!
This is what i want from all of you guys...
I will make this one reaching pure 300 watt stereo not bridge...
I will change the AC voltage from 24V AC to 30V AC
I will change trafo from 10Amps to 20Amps
So, is that dangerous or not?(2N3055 MJ2955 datasheet said that is still safe area)
But, what about other transistor, D400 and A733?
TIP31C and TIP32C(final transistor driver) datasheet said it is ok...
Please tell me, so i can follow you...
I will make this one reaching pure 300 watt stereo not bridge...
I will change the AC voltage from 24V AC to 30V AC
I will change trafo from 10Amps to 20Amps
So, is that dangerous or not?(2N3055 MJ2955 datasheet said that is still safe area)
But, what about other transistor, D400 and A733?
TIP31C and TIP32C(final transistor driver) datasheet said it is ok...
Please tell me, so i can follow you...
It's not for my HiFi...
This amplifier ONLY and ONLY driving 1subwoofer 8ohm 300watt double coils and 2 woofers 8ohm @300watt from my active crossover(basd channel)
That may have been true with the original 3055s from the 60s.
They rate them at 60V but they may all handle a little more. They wouldn't break down at exactly 60V. But the originals were probably not able to handle much more than the rated 60.
This seems not to hold true nowadays, with the newer better parts, they not only handle more, they are also much faster.
Of course it remains a possible issue and before subjecting them to higher than rated 60V, they should be tested for it.
Besides, as long as the amp isn't pushed too close to the max, the outputs aren't subjected to the full swing anyway, so they're not exposed to more than they can handle.
And a PSU with 35V rails, unloaded, will sag, so if you count for some losses in the resistors, perhaps in wiring, plus the rail sagging, they may only see a maximum Vce of around 60V from those 35V unloaded rails, which allows them to survive.
I wouldn't chance it, for any rails higher than 30V once fully loaded, the devices should be properly tested to handle more than 60V, before soldering them in place...
Which amp was that? Do you have a magazine number or date so I can find it?
Have you tried it with the newer parts? They may handle it now.
One thing is for sure, if an amp is to be designed for the 3055s and taking the manufacturer's original specs in mind, then rails should be no higher than 30V at full load, roughly, not counting for the various other losses.
This translates to basically a 50W rms on 8ohms, or 100W on 4ohms, and a 4 ohms load would require 2 pairs, and perhaps 3 if one wants to be absolutely safe on any difficult load.
Now a bridge can allow much more power, but then a 4ohms able amp, once bridged, can only be loaded by 8ohms, so we're at some 200W rms max.
To go beyond this, the rails need to be higher, and as long as the devices are first tested to handle that, then all is possible.
I can't wait to see our grounded bridge working. That one when bridged again will be a real beast, and we'll go above the 60V rating for sure.
And with enough pairs, we can drop the load some more, which is needed for the bridged bridge, as it would be loaded by 8ohms, which is 2ohms on each amp. But theoretically in the order of 800W are feasible, or a little more if we push the envelope with tested devices well beyond 60V.
Well, obviously.
And the thing is, using it that one for a sub isn't the best use either, as it doesn't even go low enough in frequency.
It probably can be improved some, so as to lower its low end roll off, possibly to 20hz or lower, which would be much better for subs.
Alright man...
After some debate, i will asking you...
Is it safe changing voltage from 24VAC to 30VAC
Then changing Amps from 10Amps to 20Anps
That will take some doing. Not just raising the rail voltages. You likely will also have to add more pairs, or you will see some smoke, and possibly flames!
That still won't do it.
Even if you take the very necessary step to make sure the devices can handle the extra rail voltage, 30Vac is far from sufficient to raise the rails high enough for that kind of power.
The datasheets don't say it's safe at all. You must not be looking at the right info.
The maximum rated Vce is 60V, that's what you're up against as a hard limit.
Now we all know the newer parts are often able to handle higher voltage than they say on the datasheets, so we count on that, but you should verify it to make sure, or you WILL get smoke.
There as well you may need parts handling some more voltage.
The ltp and its current source can easily be replaced by BC556 for example, BC556C for best beta (hfe). I don't know that D400 (2SD400), but you could use the BD139 instead. However, don't lose sight of what those devices also can handle for maximum Vce, which for the BD139/40 is 80V, so that would theoretically mean rails at not much more than 40V or so, maybe a little more.
Which means 300W is also out of the question for those devices.
Something beefier is required and with higher Vce max.
You may look at the 2SA1381/2SC3503 if they're available near you, as those handle some 300V and have the same case as the BD139/40.
But it would be prudent to add one more pair, if not more, when trying to raise the rails much more.
And then there is the issue of the beta droop from the 3055s, demanding more from the drivers, so perhaps even beefier ones would be needed, however those would not be TO126 case but likely TO220, and would require some changes on mounting on heatsinks.
Barely, as the C are 100V devices. But those don't have that much gain, although they're more rugged than the BD139/40.
Testing the devices for their breakdown voltages is a tricky proposition, so that requires some doing.
That will take some doing. Not just raising the rail voltages. You likely will also have to add more pairs, or you will see some smoke, and possibly flames!
That still won't do it.
Even if you take the very necessary step to make sure the devices can handle the extra rail voltage, 30Vac is far from sufficient to raise the rails high enough for that kind of power.
The datasheets don't say it's safe at all. You must not be looking at the right info.
The maximum rated Vce is 60V, that's what you're up against as a hard limit.
Now we all know the newer parts are often able to handle higher voltage than they say on the datasheets, so we count on that, but you should verify it to make sure, or you WILL get smoke.
There as well you may need parts handling some more voltage.
The ltp and its current source can easily be replaced by BC556 for example, BC556C for best beta (hfe). I don't know that D400 (2SD400), but you could use the BD139 instead. However, don't lose sight of what those devices also can handle for maximum Vce, which for the BD139/40 is 80V, so that would theoretically mean rails at not much more than 40V or so, maybe a little more.
Which means 300W is also out of the question for those devices.
Something beefier is required and with higher Vce max.
You may look at the 2SA1381/2SC3503 if they're available near you, as those handle some 300V and have the same case as the BD139/40.
But it would be prudent to add one more pair, if not more, when trying to raise the rails much more.
And then there is the issue of the beta droop from the 3055s, demanding more from the drivers, so perhaps even beefier ones would be needed, however those would not be TO126 case but likely TO220, and would require some changes on mounting on heatsinks.
Barely, as the C are 100V devices. But those don't have that much gain, although they're more rugged than the BD139/40.
Testing the devices for their breakdown voltages is a tricky proposition, so that requires some doing.
Looks like this time for new hunting...
Thank you man...
I will make little experiment and take the risk...
If the transformer gives 30Vac at full load, then the rails might be close to 42V, but you have to account for the drops in the rectifiers and a little bit of losses.
When idling, the voltages would be a few volts higher, but they'll sag with load, even if you have a beefy transformer such as giving 20A. Losses can't be entirely avoided.
You might lose about 1V, perhaps a little less, per diode in the rectifiers, times 2, for a full bridge, that's already a couple of volts lost, so let's say you do still have 30Vac at the transfo winding, then with the drop in the rectifiers and a little bit here and there, your rails would be about 42V, if you're lucky and with good wiring (thick wires, bars...)
But still, you're far away from your goal of 300W.
Before taking a risk, try a simulation, with the parts you think you can find.
I think you can try, if you can get them, the 2N5401/5551, which can handle all of the voltage you would need, for the front end that is, the ltp and its current source. Maybe even in place of the D400, if the simulation confirms the SOA isn't violated. Those devices handle 150-160V, plenty or head room.
For the drivers, if they can be found where you are, maybe the MJ15030/31, but they're TO220 cases. Those handle all the voltage needed, and more, and are far beefier than the BD139/40.
But for the 3055s, if you can't do the testing for their breakdown over 60V, then you are taking a big chance. It may work, it may not.
The thing is, it would only take one of the output devices to fail from breakdown, to make the amp go up in smoke, and likely take more devices down along with it.
If you really want to use those amps, as they are, but are ready to change parts, safely, there is one more thing that's possible, if available where you are of course, which is to use the "glorified" 3055s from Onsemi, with a breakdown voltage twice as high and more available power and SOA. Those are the MJ15015/16. They have basically the same characteristics as the 3055, but 120V instead of 60V breakdown voltage, 180W instead of 115W, with a better thermal resistance, and they're faster.
If you used any of those, then you have no need to test for their breakdown voltages, as they all handle far more than the 60V from the 3055s.
And with the MJ15015/16, their extra power (180W) and better SOA, can really go a long way to help handle the 4ohms load on 2 pairs.
Attachments
and also if you mean OnSemi 3055/2955 ORIGINAL, this is it...
my 2N3055/MJ2955 is original transistor from OnSemi
o=i mean OnSemi from Malaysia manufacturer
i remember my friends, he have been told me if you can buy real 2N3055/MJ2955 original from OnSemi Malaysia...
your amplifier will be longer lasting and more powerful handling speaker
Very similar, few changes, but all different devices, and one extra stage was added. But then it's definitely no longer like a 3055 amp.
Even if you used the MJ15015/16 instead of the 3055s, it would still be very much like a 3055 amp, as those are almost the same.
This one is so similar to what you got, maybe it could be possible to alter the one you have to bring it up to be like this one, but all devices are to be changed anyway.
I wonder how you could add the extra stage though,with the pcb being already made for everything on the board. Not easy to do. Could get messy.
I just wonder how available the parts are where you are. The 3055s are obviously abundant. But what about the MJ15015/16 for example? Cheap enough, if available?
I would simulate everything first. Before trying out something.
Well, original in this case would mean "newer", not the originals from the 1960s.
The originals were made by RCA, then a few others started making them, and they got popular.
I myself made an amp similar to yours, in the late 60s, with 3055, and it was a quasi, as the 2955 didn't exist yet and no PNPs existed to match the 3055 at the time. So all 3055 amps of those days were quasi.
Your "original" 3055/2955 from onsemi are thus the much newer ones, and original only means they're actually from onsemi (if they really are) and not fakes.
I haven't heard of fake 3055s anyway, they're cheap enough not to be worth faking.
Since you can have parts from onsemi right there, and they're likely much cheaper for you than any of us not from asia, you are likely to be able to get those better 3055s, the MJ15015/16. (datasheet previously attached)
I didn't look closely enough earlier, but this one has the same kind of issue as the one you have.
Although it's not 3055 based, they state a 63V rail, which would push the BD139/40, as well as the TIP41C/42C beyond they breakdown limits.
And I don't know those japanese outputs, but the same may hold true for them as well.
A better choice of parts would be preferable to be free of worries.
I think I'll simulate this one though, I wonder what it can do. And for 400W, it's obviously for 4ohms load, and 2 pairs may be a stretch for their SOA.
well, for final transistor i will screwing up mounted on the top of heat sink then soldering them together with their resistor
fo MJ15015/6 is so expensive here
simulate first then real life
that's what i will take before burning money
that's from my friend
he have been saw my amplifier
fake 3055s, in INDONESIA there are many cheap fake of them especially from manufacturer in CHINA
you know, most seller here thinking money than quality
well, i don't know if RCA making first original 3055/2955
since you said first time from RCA, i will thinking twice for the people who selling "real transistor" on their shop
then i will playing in "safe area"
back to my amplifier circuit before....
i think i have miss communication with you and other else
i tell to you and other else, my amplifier 300watt stereo
i am forget to tell you one channel is 150watt so 2 channel stereo is 300watt
i am sorry before