Quote:
Originally Posted by Argus25
The original AD149 made by philips or mullard had a beautiful bright nickel plated (on copper) finish nobody makes TO-3 transistors as beautiful looking that that anymore do they ? and the TO-3 case is obsolete. Or you could use a boring T0-220 cased epoxy silicon device.....not much of a contest is it?
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Good point, yes, I have an AD149 somewhere, and yes it is beautiful
Quote:
Originally Posted by Argus25
Also, one other interesting thing, using the EF98, it normally has a 10Meg Ohm G1 resistor. So you end up with an amplifier with two active devices EF98/OC16 & two inductive devices transformer/choke. With an input impedance of 10M, and output impedance of what your speaker is say 4R. It takes about 1 to 2V peak at the EF98 grid to get full power. That has to be one of the most spectacular power and impedance ratio transformations off all time, for just the two devices.
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To be fair, you can get an equivalent power gain from just ONE device, a power MOSFET operating in Class A... which you can use a 22MΩ gate-tie resistor with.
Quote:
Originally Posted by terrybull
The John Lindsey-Hood original version 1969 class A uses 2n3055’s and sounds very good indeed. There is a version (for electrostatic speakers) with paralleled output transistors which produced 20 watts and a later version with + - power supply to remove the capacitor from the output.
I have built several of the original and the performance belies the component count.
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JLH did produce a few rather good-performing circuits. Other people have done better technically, but that's not decrying what he managed to achieve. Not many people designed simple Class A transistor power amps. Not many want to! He did, and it has become legendary (a bit like the Mullard 3-3).
Incidentally, agree with Argus about sticking a transient suppressor across the output transistor, if operating into a transformer. It's an easy way to kill a transistor if not. A reasonable Zener (BZT03 series) is better than nothing!