I'll try to express what your saying to me considering the relative speed of devices. I would take that to mean it is more than likely to osscilate. Ca n I just add grid stoppers to take cars of that?
I meant things like avoiding long wires between the power supply and the output stage, as well as between the driver board (which BTW includes grid base stoppers) and the output transistors. There is nothing to it, really.
It is a simple Darlington amplifier
The front end does not provide enough low distortion within its design
to add much benefit with high Ft devices.
It is asking for oscillation issues.
Original Tip 142/47 are poor devices and not a well matched pair
the Ft usually not mentioned in datasheets.
Very close to older 2955/3055 in discrete form as far as Ft
not much more than 0.5 MHz closer to 0.1 MHz
2N6284/87 is a significant upgrade as far as matching pair
and offer a 4 MHz transition frequency.
Which is about the only audible improvement the simple frontend
will benefit from, and be rather stable as well.
As noted base resistors have been lowered and do fine, which
also actually improves turn on time / slew rate at high frequency.
They are available in plastic package from OnSemi
as MJH6284G and MJH6287G
Keep in mind the sankens are only TO3-P package
and offer less thermal pad rated at 130 watts 25 C temp
OnSemi Darlington is a larger thermal pad as standard T0-247
and rated at 160 watts 25 C temp
If you de rate to 75 C temp
Sanken is around 80 watts
And the OnSemi MJH holds to 100 watts
The front end does not provide enough low distortion within its design
to add much benefit with high Ft devices.
It is asking for oscillation issues.
Original Tip 142/47 are poor devices and not a well matched pair
the Ft usually not mentioned in datasheets.
Very close to older 2955/3055 in discrete form as far as Ft
not much more than 0.5 MHz closer to 0.1 MHz
2N6284/87 is a significant upgrade as far as matching pair
and offer a 4 MHz transition frequency.
Which is about the only audible improvement the simple frontend
will benefit from, and be rather stable as well.
As noted base resistors have been lowered and do fine, which
also actually improves turn on time / slew rate at high frequency.
They are available in plastic package from OnSemi
as MJH6284G and MJH6287G
Keep in mind the sankens are only TO3-P package
and offer less thermal pad rated at 130 watts 25 C temp
OnSemi Darlington is a larger thermal pad as standard T0-247
and rated at 160 watts 25 C temp
If you de rate to 75 C temp
Sanken is around 80 watts
And the OnSemi MJH holds to 100 watts
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I personally don’t care for Sanken transistors, seen to many failures. The outputs don’t require the same attention as true Push Pull design and the second stage does not provide enough drive with without a super beta transistor. The front end cascode section to help the linearity. It’s just an old simple design. I built 4 of these one in the closet since 1984, however it has 2N5922 match pair, I believe that correct part number.