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Post by pickupcentral on Dec 12, 2006 21:03:31 GMT -7
Forgive me if I missed something. If this was addressed on another thread, perhaps someone could point me to it and I'll slink away.
Some amps are cathode bias, some are fixed. It seems that EL84 tend to be cathode bias, but not exclusively (Mesa has 6L6 and EL34 amps that are, and I'm sure there are fixed-bias EL84 amps).
What are the sonic differences? If negligible, why not make them all that way for ease of use? It isn't keeping me from buying a fixed-bias amp (money is!), but all amps in my current rotation are cathode bias (Rx, Maz 18, Ghia). Can fixed-bias amps be modded for cathode bias?
Just curious! -Phil
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Post by nathan38 on Dec 12, 2006 21:12:37 GMT -7
you can mod a fixed bias amp for cathode bias.
as a rule cathode bias compresses more.....usually lower plate voltage too.
I'm no tech...but it has something to do with plate voltage, one being referenced to ground, the other to a negative voltage.......hopefully, someone will corect me and fill in the blanks.
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Post by billyguitar on Dec 13, 2006 9:06:06 GMT -7
I've converted several amps myself to cathode bias, BF Super Reverb, BF Vibroluxe Reverb, and both of my 1957 Bassmans. I followed the instructions in one of Gerald Weber's books. The title of the chapter is something like, "Can You Make Your Amp Meow?". You get that meow kind of sound when you've got the amp cranked and you hit and hold a note. The funny thing is the amp that did that the most for me was a fixed bias Marshall 1987X but as a rule the cathode bias helps that in amps that don't do it naturally. When I first started reading up on my old vintage Fenders, 1950 Pro, 1950 Super, 1956 & 1959 Tweed Deluxes etc., I noticed that most of those were cathode bias. I concluded that was one of the things I liked most about them. Then Gerald Weber wrote about it so I tried it. Here are the benefits, less overall volume, much better sustain and less stress on the old speakers. You can also play around with different rectifier tubes and see how that affects the sag. 5Y3s sag the most, then 5V4, then 5U4 and finally a good 5AR4 almost sounds the same as stock. For the most part these are reversible mods and other than the time to put them back to stock, won't really hurt the value.
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Post by skydog958 on Dec 17, 2006 9:50:30 GMT -7
I wonder what the KT45 would sound like with cathode bias
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Post by osostrings on Dec 19, 2006 15:56:15 GMT -7
I wonder what the KT45 would sound like with cathode bias I'd love to hear that - probably jaw-droppingly rad.
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