Equa amplifier ELEKTOR Dec 74 https://ia800804.us.archive.org/20/items/ElektorMagazine/Elektor[nonlinear.ir] 1974-12.pdf
At least it wasn't in the German ELEKTOR edition of December 1974. Must have been much earlier.
Edit: Found it. In Germany it was published in December 1972. Note there are differences between th English and the German version of table 2, the so called compensation networks in the drivers' emitters. While in the German version the BA148/22Ω/12n combo, as shown in the complete schematics, is called the best one, two years later in England it was swapped with 1N4002/0Ω/27n.
Best regards!
Edit: Found it. In Germany it was published in December 1972. Note there are differences between th English and the German version of table 2, the so called compensation networks in the drivers' emitters. While in the German version the BA148/22Ω/12n combo, as shown in the complete schematics, is called the best one, two years later in England it was swapped with 1N4002/0Ω/27n.
Best regards!
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Actually I don't know - it is some military surplus. There were two boards, indeed - the first one with the original transistors KT903 and the second one shown on the picture. The original didn't draw my attention and was thrown in the bin immediately. I keep the second one because of the unusual transistors mounted. If you look closer you can see how they managed to fit the TO-3 parts like 2N3055 onto the heatsinks not designed for them.
I don't think it was initially manufactured this way - probably the 2N3055 were replacement of faulty KT903 or something.
What about the Czech's KD607/617 - yes they were great transistors for their time and I successfully implemented them in several amplifiers during the 90-ties.
I'm too lazy for searching the datasheets but I think their max. voltages and power were lower than the 2N3055 ones. The biggest problem at that time actually was that the 2N2955 was unobtainable and hence the impossibility for building complimentary output power stages.
Wrt KD607/617: I had some closer look. They're superior over 2N3055's just in terms of Vce and fT, but inferior in their dissipation ratings. In some other place they were recommended as a replacement for RCA's 40636.
And 2N2955 is astonishing: I'm quite sure that 2N2955 originally described a small signal transistor in TO18 package, and related dataseheets are still to be found. In those days, i.e. 50 years ago, the magazines warned not to look for 2N2955's as PNP power devices due to this fact, but Motorola's MJ(E)2955's or TI's TIP2955's instead. Obviously the designator has changed somewhen, as indeed TO3 2N2955 can be found today.
Another hint for a 2N3055 complementary was the BDX18.
Best regards!
And 2N2955 is astonishing: I'm quite sure that 2N2955 originally described a small signal transistor in TO18 package, and related dataseheets are still to be found. In those days, i.e. 50 years ago, the magazines warned not to look for 2N2955's as PNP power devices due to this fact, but Motorola's MJ(E)2955's or TI's TIP2955's instead. Obviously the designator has changed somewhen, as indeed TO3 2N2955 can be found today.
Another hint for a 2N3055 complementary was the BDX18.
Best regards!
I have a lot of Tesla TO3s, I never paid attention to them, I had them a long time ago in a lot from a company that worked for the military and I have many others with references " exotics" on which I have never found any information.
I had the same case with the father of a friend who worked in the military division (CIFTE for CFTH which will later become thomson CSF then, Thales ) in charge of passing tubes to the torture test before being validated for the army, all the references of the tubes were coded and he told me gave a lot of tubes with a sheet that allowed me to convert the references in the civilian world.
@Kay P - The original 2N2955 was listed as a TO-18 small signal germanium transistor in my ageing Towers International Transistor Selector book, pretty much the same spec as a PNP version of a BC108. I was not aware that the JEDEC spec. had changed, but the only reference I saw to a TO-3 2N2955 was a UTC device. Most people recognise that Motorola introduced the MJ2955 as a 3055 complement - but there seemed not to be much confusion in the early days.
BDX18 was not a complement to the original 2N3055 though it was touted to be. No true complement to the old hometaxial 2N3055 was ever manufactured in production. The old datasheet I have for BDX18 suggests it could handle 60V at 1.9A - but I never tested them as nearly all other PNP devices had a worse SOA.
BDX18 was not a complement to the original 2N3055 though it was touted to be. No true complement to the old hometaxial 2N3055 was ever manufactured in production. The old datasheet I have for BDX18 suggests it could handle 60V at 1.9A - but I never tested them as nearly all other PNP devices had a worse SOA.
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Back in those days I wouldn’t even TRY to obtain a PNP bigger than a TIP42. Surplus 2N3055’s for about a buck - higher power pulls for about the same money. Biggest challenge was finding a suitable PNP driver - everything else bigger than a TO-92 can be forced to be NPN. Even before knowing what I as doing I realized that TIP drivers was a no-no - it made amps harder to stabilize and sounded like $#1+ after killing enough of the open loop frequency response to get it to quit oscillating. Pulls from expensive receivers that had blown and been junked was the primary source of decent PNPs.
Now, PNP Ge’s we’re all over the place. Couldn’t afford new ones either, but I could get pulls any day of the week. Usually could find data, too. I had a Jap transistor manual. Tried pairing one with a RCA 2N3055 and running up at 70 volts, but quickly found out what second breakdown is. Took out the 3055, too.
Now, PNP Ge’s we’re all over the place. Couldn’t afford new ones either, but I could get pulls any day of the week. Usually could find data, too. I had a Jap transistor manual. Tried pairing one with a RCA 2N3055 and running up at 70 volts, but quickly found out what second breakdown is. Took out the 3055, too.
Well, MJ2955/2N3055 were what Elektor suggested back in 1972, especially when they said that compensation networks in the driver emitters were designed to work just with them. So I did anything to get my hands on 'em.
Later I also had TI TO-3P BD245C/246C's and even BD249C/250C's in my EQUA's. My first integrated amplifier with EQUA's is still in use. I've given it to my younger son. They're running MJ15003/15004's now. But even these blew from time to time, until I recognized the VAS/CCS transistors with their insufficient Vce rating as the most probable failure cause.
Once we had a specific ELECTOR branch here at DIYAudio, where I described a rather tricky tracedown of an uncommon failure in one of the the drivers.
Best regards!
Later I also had TI TO-3P BD245C/246C's and even BD249C/250C's in my EQUA's. My first integrated amplifier with EQUA's is still in use. I've given it to my younger son. They're running MJ15003/15004's now. But even these blew from time to time, until I recognized the VAS/CCS transistors with their insufficient Vce rating as the most probable failure cause.
Once we had a specific ELECTOR branch here at DIYAudio, where I described a rather tricky tracedown of an uncommon failure in one of the the drivers.
Best regards!
My first amps were QC for that reason, using RCA2N3055. Drivers cost almost as much or more in some cases, I recall. Mostly 40361/40362. Blew a few of those but the original pair of 3055's I still have - now souveniers of the time. Survived a couple of shorts even with simple SOA protection.
My hifi changed to Bailey design with MJ481/MJ491 which I suspected later were probably gain drop-outs from 2N4915/4905 which would have been better (higher minimum gain) - but cost more. After blowing several pairs of 481/491 (they sounded great BTW -when they worked) I moved to 2N3055/MJ2955 epi and still have a 50W stereo working with these.
Also used 2N2102 and 2N4036 drivers though for some reason these were never as common in UK shops, probably because 40361/40362 had become popularised -think these were used in the Quad 303 as main drivers as well as Bailey.
My hifi changed to Bailey design with MJ481/MJ491 which I suspected later were probably gain drop-outs from 2N4915/4905 which would have been better (higher minimum gain) - but cost more. After blowing several pairs of 481/491 (they sounded great BTW -when they worked) I moved to 2N3055/MJ2955 epi and still have a 50W stereo working with these.
Also used 2N2102 and 2N4036 drivers though for some reason these were never as common in UK shops, probably because 40361/40362 had become popularised -think these were used in the Quad 303 as main drivers as well as Bailey.
Two bucks apiece (and $2.19 for MJ2955 when they started carrying them) was a stretch for a 15-year-old. Especially when what you really wanted/needed were 120V transistors to make 100 watts at 8 ohms. I did stretch the 3055’s to 80, 85V but no more. That gets you about 60W, real world after voltage sag. Even the usual mail order outfits refused to support much more than this. It wasnt till Consolidated Electronics (an offshoot of Newark, who would actually deal with small timers) came along when I could get real transistors. By then I could afford $4 2SD424’s, and a wide array of Jap sustsained-beta drivers for under a buck. Sure, the TV shops in town would have always sold you an ECG284 - for $33 apiece. CEI had them too - for $10.95. Retail markup was typically 3X and everybody stuck to that like glue. You COULD NOT use 2N3055’s to rebuild an ailing CS800 no matter how much liberties you took with ratings, but D424’s hell yeah.
Well, I chose them because I thought they're more rugged than the older MJ2955/2N3055's, as they could stand higher voltages and higher dissipation ratings, and I hadn't recognized the Vce issue with the VAS/CCS BC107/177's yet. The EQUA's that are still in use by my son are fed from a 200 VA 50 Vac power transformer.
Best regards!
Best regards!
Well, yesterday I dug out an old folder containing schematics, build advices etc. that I began collecting in the 1970ies. I decided to show some of them to you, even though they're in German.
The 1st one is ELEKTOR's EQUA amplifier that we discussed just recently. I've built about one dozen of these units, mostly for friends.
2nd one is the most powerful of a series of amplifiers that ELEKTOR pubished in their two years of existence prior to the EQUA which followed in December 1972. They called them EDWIN. Note the unusual quasi complementary output stage with a quiescent current of 0 (zero!) mA through the 2N3055's that take over output current when the voltage drop over the driver's resistors of 12 Ω exceeds their Vbe threshold. I built an integrated stereo amplifier for a friend, using a pair of these plus the control preamplifier called B17 by Oppermann, the vendor.
3rd one is a power amplifier developed by SIEMENS and originally published by the German Funkschau magazine in January 1971. Of course they're just a rip-off of RCA's quasi complementary power amps from the 1970 Transistor Manual, using European/German transistors, especially the BD130, a 2N3055 equivalent. I built two or three pairs of the 60 watts version which proved to be stable and reliable even in guitar amp service. Note the 120 W version that stretches the Vce ratings of the two pairs of power devices.
The 4th one was an ambituous project, a 200 W amplifier using two MJ2955/2N3055 pairs in series! Never build one of these, mostly out of monetary reasons (I was a schoolboy then). All in all, this design may be regarded as a crutch from out present view, but hey, there weren't any higher voltage PNP power devices back in those days, or they were hard to obtain for us hobbyists and very expensive.
Best regards!
The 1st one is ELEKTOR's EQUA amplifier that we discussed just recently. I've built about one dozen of these units, mostly for friends.
2nd one is the most powerful of a series of amplifiers that ELEKTOR pubished in their two years of existence prior to the EQUA which followed in December 1972. They called them EDWIN. Note the unusual quasi complementary output stage with a quiescent current of 0 (zero!) mA through the 2N3055's that take over output current when the voltage drop over the driver's resistors of 12 Ω exceeds their Vbe threshold. I built an integrated stereo amplifier for a friend, using a pair of these plus the control preamplifier called B17 by Oppermann, the vendor.
3rd one is a power amplifier developed by SIEMENS and originally published by the German Funkschau magazine in January 1971. Of course they're just a rip-off of RCA's quasi complementary power amps from the 1970 Transistor Manual, using European/German transistors, especially the BD130, a 2N3055 equivalent. I built two or three pairs of the 60 watts version which proved to be stable and reliable even in guitar amp service. Note the 120 W version that stretches the Vce ratings of the two pairs of power devices.
The 4th one was an ambituous project, a 200 W amplifier using two MJ2955/2N3055 pairs in series! Never build one of these, mostly out of monetary reasons (I was a schoolboy then). All in all, this design may be regarded as a crutch from out present view, but hey, there weren't any higher voltage PNP power devices back in those days, or they were hard to obtain for us hobbyists and very expensive.
Best regards!