Thread: Quad FM3 tuner.
View Single Post
Old 22nd Apr 2013, 8:41 am   #5
Mike Phelan
Dekatron
 
Mike Phelan's Avatar
 
Join Date: Nov 2003
Location: Near Leeds, West Yorkshire, UK
Posts: 4,609
Default Re: Quad FM3 tuner.

Quote:
Originally Posted by Radio Wrangler View Post
TR4 TR5 D1 look a bit odd. It seems that without a signal they reduce the long tail bias current, so the collector loads go high and the emitter followers make both bulbs bright.

Less light for more signal does seem counter intuitive.

David
Interesting point, David. It certainly gives no light for no signal, and I think that in those circumstances, TR8 is turned on fully, thus the long-tailed pair are also on, and their collectors are nearly grounded.
I might open the unit up and measure all these voltages and check the polarity of D1 isn't an error in the maker's diagram, just for interest!
__________________
Mike.
Mike Phelan is offline