Tonal Characteristics of Cathode Biased Amps...

[Aint Life Hell?]

Hello,
All three of my amps happen to be cathode biased.
A lot of the vintage amps I like are not cathode bias, but nearly all the newer models are. Some amps even allow you to choose between cathode bias & non cathode bias.
Okay, my question: is there a detectable tonal difference in amps that are & those that are not cathode bias?
Thanks!
-m

[VacuumVoodoo]

Hi,

here is a link to an old article (http://ken-gilbert.com/images/pdf/fixbias.pdf) on the subject

[Aint Life Hell?]

Thanks, Man.

[jetlag]

I added a switchable cathode bias scheme for the power tubes in my BF pro reverb. At first I was dissapointed in how little difference there was in sound and response. Then I omited the bypass cap and really heard (and felt) a difference. I got much more drop in power, compression and less speaker dampening (speakers felt looser) when I omitted the cathode bypass cap. So that's how I left it. Doing that and then observing other things later made me realilze that there are other things going on in some cathode biased amps that contributed as much or more to the sound/response as the actual cathode biasing. For example, some amps don't have a choke and use a power/limiting resistor. Those amps are really compressed despite the use of a cathode bypass cap. They also really round off the attack of notes, giving everything an open vowel singing quality. Other amps place the choke in a different spot than what most amps today do. That also influences compression and attack/response. So there are alot of things going on! What I realized was that switching to cathode bias alone wasn't that big of a difference. To really notice a difference (and to sorta emulate some of the choke placement or lack-of-choke stuff) my ears told me to skip the bypass cap. BTW - in that Pro Reverb, I still run the amp stock in fixed bias about 75% of the time. It's just those low volume gigs where I really dig the cathode bias.