UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

Neil Purling · 6th Sep 2010, 10:10 am

f.cooper:
How do your Mullard reference books rate the hfe of the OC71 & OC75?

I bought a kit of bits. The kit is to build a radio from a circuit in a book.
The audio stage has the emitter of the first OC71 wired to the +ve rail, no emitter resistor.
I wondered why there wasn't something with its associated bypass capacitor.
The supplier of the kit has tweaked the circuit to add a 1K emitter resistor & 22uf bypass and employ OC81's in place of the two OC71 transistors.
I am trying a emitter resistor & bypass with the OC71's in case this makes an improvement without fitting OC81s.
If the audio stage is weak as originally planned with OC71's I will make note and move on based on what help I get here.

6th Sep 2010, 10:10 am	#7
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,087	Re: Transistor Choice in radio project f.cooper: How do your Mullard reference books rate the hfe of the OC71 & OC75? I bought a kit of bits. The kit is to build a radio from a circuit in a book. The audio stage has the emitter of the first OC71 wired to the +ve rail, no emitter resistor. I wondered why there wasn't something with its associated bypass capacitor. The supplier of the kit has tweaked the circuit to add a 1K emitter resistor & 22uf bypass and employ OC81's in place of the two OC71 transistors. I am trying a emitter resistor & bypass with the OC71's in case this makes an improvement without fitting OC81s. If the audio stage is weak as originally planned with OC71's I will make note and move on based on what help I get here.