I have here the schematic for the Maplin 225 Watt amplifier.
For what it's worth the amp uses a pair of 2N3055 and a pair of the complementary MJ2955. It doesn't specify "H" type or anything like that.
The power rails are + & - 50>55 Volt off load according to the info here and power is quoted as 225W into 4R with one channel driven dropping to 160W with both channels driven and 146W/112W into 8R. Not the stiffest of PSU's.....
Drivers are BD711, BD712 and the output stage is a Darlington emitter follower.
In every other respect the amp is absolutely conventional and simple.
If you look at Rod Elliott's P3A and arrange the output stage for emitter follower rather than CFP then you've kinda got it....
Hope this helps
For what it's worth the amp uses a pair of 2N3055 and a pair of the complementary MJ2955. It doesn't specify "H" type or anything like that.
The power rails are + & - 50>55 Volt off load according to the info here and power is quoted as 225W into 4R with one channel driven dropping to 160W with both channels driven and 146W/112W into 8R. Not the stiffest of PSU's.....
Drivers are BD711, BD712 and the output stage is a Darlington emitter follower.
In every other respect the amp is absolutely conventional and simple.
If you look at Rod Elliott's P3A and arrange the output stage for emitter follower rather than CFP then you've kinda got it....
Hope this helps
You could of course use a quasi complementary output stage if you really must use just 2N3055's..... and you add some more output pairs if have loads available...
Of course we don't know what percentage of these Maplin amps went bang due to excessive voltage on the output devices!
The poor regulation of the PSU could have helped it survive due to the fact that if the amp was being thrashed, and assuming a stereo pair being run from one supply, the rail voltages would probably have dropped a fair bit by the time it hits the rails
Of course we don't know what percentage of these Maplin amps went bang due to excessive voltage on the output devices!
The poor regulation of the PSU could have helped it survive due to the fact that if the amp was being thrashed, and assuming a stereo pair being run from one supply, the rail voltages would probably have dropped a fair bit by the time it hits the rails
The topology about
Popular Electronics February 1967
could be a good solution. If power isn't enough, bridge mode (instead higher voltage) is the right way. But please note: 4 times more power means only + 6db by SPL.
the associated thread is here:
http://www.diyaudio.com/forums/solid-state/140988-vintage-brute-70-40411-clone.html
Of course we don't know what percentage of these Maplin amps went bang due to excessive voltage on the output devices!
The poor regulation of the PSU could have helped it survive due to the fact that if the amp was being thrashed, and assuming a stereo pair being run from one supply, the rail voltages would probably have dropped a fair bit by the time it hits the rails
I ran a mono version on a mobile disco for years and it never had any problems. It really was very loud in social club size venues.
If there were problems then i am sure Maplin would have discontinued it pretty quickly or come up with an updated version.
I am pretty sure it was 225WRMS and not 225W peak, as I say it was very loud.
Maplin 225WRMS amplifier.
An externally hosted image should be here but it was not working when we last tested it.
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cheers nigelwright i reckon that maplin one will do the trick just nicely. Allthough a quasi design using mostly npn would use more of them up. But iam very thankful you put that design up could be very useful. So if you used them for disco's i reckon fold back or even front of house if it was just vocals this amp would do ok also.ON Semiconductor MJ15015: 15 A, 120 V, NPN Bipolar Power Transistor
This is a better solution than using the cheaper 2n3055/2n2955 variety.
Its amazing how cheap we can get when it comes to saving a few dollars on
semiconductors yet we will spend mega bucks on those magical mystical
devices promising the return of our youth. Use something with a proven track
record. It makes more sense to me to do something once and have it correct.
Seen too much of the 2n2955/2n3055 crap on the repair bench and always
upgraded to MJ15015/MJ15016's and didn't see the stuff come back. If my
memory is correct NAD had some products that used the 2n2955/2n3055 stuff
and it ran at the maximum rail and it always came back in for repair. My
suggestion is this ...do a group buy. Someone takes orders for semiconductors
and purchases a lot of 500 or so transistors to get a favorable price and then
dispense them for this project or a project similar to this. I've read the
ratings on the 2n2955/2n3055's but unfortunately never ran across anything
that survived the higher voltage rails. Just my .02
This is a better solution than using the cheaper 2n3055/2n2955 variety.
Its amazing how cheap we can get when it comes to saving a few dollars on
semiconductors yet we will spend mega bucks on those magical mystical
devices promising the return of our youth. Use something with a proven track
record. It makes more sense to me to do something once and have it correct.
Seen too much of the 2n2955/2n3055 crap on the repair bench and always
upgraded to MJ15015/MJ15016's and didn't see the stuff come back. If my
memory is correct NAD had some products that used the 2n2955/2n3055 stuff
and it ran at the maximum rail and it always came back in for repair. My
suggestion is this ...do a group buy. Someone takes orders for semiconductors
and purchases a lot of 500 or so transistors to get a favorable price and then
dispense them for this project or a project similar to this. I've read the
ratings on the 2n2955/2n3055's but unfortunately never ran across anything
that survived the higher voltage rails. Just my .02
For those of you wanting to pinch Penny's I checked the price of a single lot MJ2955 verses a MJ15015 on Mouser. The MJ2955 was $2.57 a single and the MJ15015 is $2.34 and the price drops further when dealing in large quantities.
Imagine that a transistor more suited to the task at a lower price. This one won't go up in a puff of smoke when dealing with 55volt rails.
Imagine that a transistor more suited to the task at a lower price. This one won't go up in a puff of smoke when dealing with 55volt rails.
by post #5 about
RCA transistor app notes / amplifier design - UK Vintage Radio Repair and Restoration Discussion Forum
I read:
Actually the 40636 might have been dropped from production as the Hometaxial process was phased out (anybody know when that was?) because it was a 2N3055 selected for high Vceo. The Hometaxials had 100% SOA and the early epitaxials probably couldn't meet the spec of the 40636 at high voltages.
Means this, that there are also high Vceo "2N3055" versions on the marked, i. e. without labeling of other type number?
Who knows more about the function (detailled procedure) of such a selection process to find out the maximum Vceo ??
RCA transistor app notes / amplifier design - UK Vintage Radio Repair and Restoration Discussion Forum
I read:
Actually the 40636 might have been dropped from production as the Hometaxial process was phased out (anybody know when that was?) because it was a 2N3055 selected for high Vceo. The Hometaxials had 100% SOA and the early epitaxials probably couldn't meet the spec of the 40636 at high voltages.
Means this, that there are also high Vceo "2N3055" versions on the marked, i. e. without labeling of other type number?
Who knows more about the function (detailled procedure) of such a selection process to find out the maximum Vceo ??
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There is no logic here like that. These hobbyist's just want to salvage some old devices out of junk and slap together another abomination. Same as the typical walmart shopper or Ebay amp kit buyer , MTBF and durability mean nothing. I guess it is a challenge (or fun), to not derate anything or use antiquated devices and designs. It might be a good lesson for some to fry some equipment and learn the hard way.The "Next time" might be taken a little more seriously.
OS
OS
That brings up the interesting question of decision making, experience and knowledge. Turns out good decision making is about the last faculty to develop in the late 20's or early 30's according to some.
The last amp shown with 44 volt rails will work. The issue is still matching the junk box transistors to what their performance really is. That will be educational. Which will lead to an increase in knowledge. So building one and getting it to work should be a useful experience.
In a Class AB amp, the output transistors conduct in only half cycle. Zero to +rails for the top half and Zero to -rails for the bottom transistors.
Only in Class A are the output transistors subjected to rail to rail voltages.
They are still subject to the rail to rail voltage. Just because they are shut off does not obviate the requirement.
Take the top transistor conducting hard and near saturation. It's emitter voltage is near the upper rail. So the lower transistor is subject to the bottom rail + the top rail - the VCE sat of the upper transistor.
Even though the device is shut off, there is no current limiting component to prevent punch through of the collecto to base junction when the reverse breakdown is exceeded.
Take the top transistor conducting hard and near saturation. It's emitter voltage is near the upper rail. So the lower transistor is subject to the bottom rail + the top rail - the VCE sat of the upper transistor.
Even though the device is shut off, there is no current limiting component to prevent punch through of the collecto to base junction when the reverse breakdown is exceeded.
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I think it's a good idea, I don't ascribe to all the party-pooping responses on this thread telling you to go get a better transistor. The spirit of DIY is alive in just what you are proposing to do with your junk box parts.
It turns out I have a bunch of 2N3055H's on heatsinks and I'm doing exactly that - building something with them. In my case I'm building a JLH69 Class A amplifier. It's only good to 10W - 15W but I think it will be plenty for me.
A simple topology would be my suggested starting point:
2N3055 Power Amplifier
p.s. I suggest there is some benefit to be gained by paralleling these output devices so that the first several W of power output result in a current through the output devices that is roughly 700mA or less, which keeps the devices operating where their Beta is healthy.
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Not hard if you switch inputs, get noise pickup from storms, etc.
It only takes a very short peak to cause breakdown and zot the entire output section.
I recently tested some 70 P-FETs for breakdown. Four out of the 70 did NOT meet manufacaturers specificaitons with the worst at only 47V for a 60V rated part. The highest breakdown I saw was 115V. The parts were screened from a process that produced 90V, 60V and 40V parts so it is not surprising that some were over 100V breakdown.
These were qual samples from over 15 years ago.
Has anyone tested older 2N3055s for breakdown? I've got some from the 70s some where. I may test them to see how good/bad they really are.
The original 2N3055s were not screened parts, so I suspect breakdown will be pretty close to the advertised breakdown.
When I first started out in designing, all I could afford were the 2N3055. The Mj15003/4 were hard to come by and if available, were very costly. I simply couldn't afford to blow up 2 pairs of Mj15003/4.
The 2N3055 do have their shortcomings when compared to newer devices but they were great for my education. It forces one to even work harder to overcome the limitations. As "Gimp" rightly pointed out, the 2N3055 are vulnerable to overvoltage for today's "high-powered" amps (+/- 55V rails). But for learning purposes, it's actually bad to start with today's excellent devices.
The 2N3055 do have their shortcomings when compared to newer devices but they were great for my education. It forces one to even work harder to overcome the limitations. As "Gimp" rightly pointed out, the 2N3055 are vulnerable to overvoltage for today's "high-powered" amps (+/- 55V rails). But for learning purposes, it's actually bad to start with today's excellent devices.
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