Dx Blame ST together Dx Super A

[lanchile]

Wow, you have a good team there! and you have created a very nice amp "again". Congratulations!

[destroyer X]

Yes...good guys around ... this helps me a lot, i cannot make layout... i do not know how to do, also i dislike to learn...and i have strong suspections i am too much stupid to learn.

regards,

Carlos

[homemodder]

I havent asked from which manufacturer you get them yet. It s interesting as I got my hands on a large amount of old philips stock, these transistors are better performance wise in some aspects than even toshibas 2sa1930/2sc5171. Looking at datasheet one sees that for the usual 20 30 ma at which the drivers are biased the ft of the BDs are at 150 Mhz while the toshibas only manage max 50Mhz, also the toshibas have much higher paracistic capacitances. The only hiccup is the Vce and SOA. SOA can be bettered by parraleling 2.
Ive compaired the philips ones to onsemi but the onsemi ones arent as good as the old philips, reason I ask.

[destroyer X]

post a few minutes ago.... and i have perceived, clearly, the curiosity in your vibrations.

THen, as an answer to your call i was trying to remember, as yesterday i got out to see doctors and have not inspected the transistor brand name for you.... it seems it is a fairchild, but not sure.

I promisse, more 8 hours i will make a picture to show you the transistor.

I am having concerns because i found one strange current in my circuit, and i do not know from where this current comes...i am deeply concern that i may have a failure...if i have a failure, then i have discovered the way to make wonderfull amplifiers, i have to discover to repeat the stuff the day i want.

Man, i am so confused, i found strange current in the VAS...so confused, exactly in that BD139, and it is hot, too much hot to 1 or 2 watts, and it is not burned, also have not a leakage... VBE is fine and voltages too... also not oscilating.

I just cannot way to leave the job to see what is going there.

Be aware Home, i can feel your vibrations, i can feel from some guys...this means i can understand, remotely, the mood of your thinking, not the ideas, but the mood, the emotion behind the words.... we call this "vibration"... this means also, please, do not call me...because some kind of ring will play in my brain and youir name will appear in my mind...telepathy maybe if you want.

regards,

Carlos

[AndrewT]

I have seen the Philips fT quoted as far apart as 50MHz to 190MHz.
Is this down to the difference between NPN & PNP, or is it that fT spreads are enormous?

[homemodder]

Andrew, I dont know what the other brands but the philips parts were BC6 series parts put into TO126 package, this from the mouth from an insider at philips. Also if you look at the spice models youll notice that the same model is used for the bc and bd parts. Now if you have a look at the bc6 series youll notice that their ft can reach 160 Mhz at 50 mA and this at Vce of 5V were as most usually quote this figure at 10 V (at 10V the Ft will be even higher so no surprise at the figure of 190Mhz which is possible). More important is that a very high speed is reached at the currents drivers usually are biased at, onsemi drivers mje15034,s barely reach 20mhz at these currents and have 4 or 5 times as much parracitic capacitances. BDs used at their max Vce perform excellently.

[AndrewT]

I accept that ONsemi's MJE1503x series are a quite different type from the Philips 139/140.
No argument there. I would never swap these parts. They are for different parts of the circuit.

But it's the 139/140 that concerns me. Many say the Philips are best. There are many clones out there and few if any seem to quote parameters for Cob, fT etc.
How do we identify the good from the average?

[homemodder]

Thats what Ive been experimenting on, with philips parts (2 in paralell) I get better THD figures than highly acclaimed 2sa1930/2sc5171 transistors in the same amp. Using Onsemi devices results werent so spectacular although they still showed slight improved figures over the toshibas. I would now like to try fairchild parts as their bc639 is rated at 100 V.
The mje drivers are actually ill suited for class AB, who biases their drivers at 100 or 200 mA which is where these show some kind of respectful speed ??. I got a clear picture now as to the reason Krell in some amps parralel upto 5 devices to act as drivers instead of using high current ones like the mje,s.

The best way if you have the equipment is to use a curve tracer and investigate.

[destroyer X]

I just cannot wait to leave my job to do what i love to do.

regards,

Carlos

[destroyer X]

I do think i have reached 9 to 1 ratio if you compare second to third harmonic.

Simulator data at 80 Watts RMS into 8 ohms.... 750 milivolts peak entering the amplifier.

I have tried second VAS with one more BD139 in parallel, this have reduced THD in a very small number (1/1000) ... but the 9 to 1 ratio (second to third harmonic) was changed to 4.5 to 1.

I will listen anyway.... i want to listen real life.

regards,

Carlos