SS rectifiers, biasing, headroom, BF Fender...

cerebralpaul

Member
Messages
276
OK, so I put a SS rectifier in my BFSR- to get the bias within proper parameters I had to turn the bias pot all the way down and it's still on the high side- so my question is: since my tubes are now running "hot" do I now have LESS headroom than if I just left the tube recto in there and ran the bias on the "cool" side?
 

GearHeadFred

Member
Messages
1,639
I have experimented with SS and tube rectos in my BFSR.. my guess would be no - that the SS recto will give you more headroom.. BUT how hot are the tubes running?

Why not add a resistor to the bias pot to give a larger range?
 

Blue Strat

Member
Messages
30,687
What GearHeadFred said:) How hot is hot?

Bottom line is, how does it sound? That's the only thing that counts.
 

cerebralpaul

Member
Messages
276
Well soundwise its fine- a tad tighter bass/more headroom but not a huge difference. Numberwise I forgot exactly, I printed out a reference from somewhere(maybe it was your site Mike?) and I think it might have been around 375v and 55ma which was just within "safe" parameters but definitely "hot". When I only heard a slight difference in headroom I got to thinking about my original question- if I put the tube rectifier back in and ran the tubes "cool" might that make a bigger difference?
 

Blue Strat

Member
Messages
30,687
Are you sure you have 375 or the plates? If you do, you've got a problem. You should have closer to 475 with a SS rectifier.

If it is 475, you're running at 26 watts which is well out of the safe zone.
60% of max dissipation is good, anything higher is a waste of energy (heat) and tube life.
 




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