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Old 6th Sep 2010, 12:05 am   #6
Join Date: Oct 2006
Location: Stoke-on-Trent, Staffordshire, UK.
Posts: 128
Default Re: Transistor Choice in radio project

Looking back through the Mullard data books (1965-1967) they kept moving the goal posts with regard to how hfe was expressed.

For the OC81 in 1966/67 it was hfe (Vce = -6v; Ic =1mA Typical 80

For the OC81 in 1965/66 it was hfe min ( Ic = 300mA ) 45

The OC81 were probably at least the third generation of low power audio O/P transistors.

The OC81D was specifically for use as a driver and consequently had lower current capability, lower hfe and also lower power.

The OC72s were amongst the first generation.

Later on the OC81s were phased out and replaced by the AC128 ( AC127 an NPN could be used to complement) , this enabled the driver and O/P transformers to be eliminated thus a cost saving.

As it has been pointed in another thread various audio packages ( LFK4 etc )were distributed where supposedly the output pair were matched.
Best Regards Fred


Last edited by f.cooper; 6th Sep 2010 at 12:21 am.
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