|
Post by ruger9 on Feb 29, 2008 14:23:34 GMT -7
I'm confused. I was reading Myles' info on the Mazerati today, and in one section he talks about a "fixed bias phase inverter", but also says the Maz is "split load biased", then talkes about how cathode-biased amps heat up when the tubes aren't matched... making me assum the Maz is cathode biased.
What IS the Mazerati's power section, bias-wise?
|
|
|
Post by billyguitar on Feb 29, 2008 16:06:46 GMT -7
Cathode bias.
|
|
|
Post by Curt on Feb 29, 2008 18:37:40 GMT -7
Read the bias section on the Z web site. All Doc's EL84 amps are cathode biased.
|
|
|
Post by Phil (aka Phil) on Mar 1, 2008 6:35:31 GMT -7
Don't let the "split load bias" thing throw you off. Split load biasing is a design technique which uses a separate bias resistor for each "half" of the quad of EL84's. What this means is that you don't need a matched quad of EL84's like you do in most 4 X EL84 amps; but what you *do* need is matched duets on each side. SO, you could theoretically run a matched pair of #6's on one side and #5's on the other, or even a set of #6's on one side and a matched set of NOS Mullards on the other, etc. Whatever you do, DON'T just run two tubes on one side and none in the other side looking for lower volume and breakup. That doesn't work. As far as I know, the later Mazerati's, Stangray, RxES, and Maz Sr. NR (at least) are split load biased. I think the GT probably is as well, but I haven't taken her out of the head cab yet- trying to keep the Mojo inside ;D Split load biasing definitely adds to the bass, sustain, and "balls" of an amp.
The fixed bias phase inverter is a design that I've never seen on an amp outside of the Carmen Ghia and Mazerati. This "biasing" refers to the phase inverter tube, NOT the EL84's in the power section. 99% of the time preamp tubes are cathode biased in a fashion similar to cathode biased power tubes. When people say "cathode biased amp" they are referring to how the output tubes are biased, not the preamp tubes. Otherwise almost every amp ever made could be called "cathode biased"!
Cathode biased amps do heat up considerably more when matched power tubes are not used...it's one of the things (along with inadequate ventilation) that caused AC/30's to have the reputation of being fire hazards.
|
|
|
Post by ruger9 on Mar 1, 2008 7:15:41 GMT -7
Thanks guys!
|
|
|
Post by myles on Mar 19, 2008 8:58:30 GMT -7
I may be wrong here but I believe only the carmen ghia has a fixed bias on the phase inverter and the mazerati has a conventional cathode biased phase inverter. The Mazerati also has a feedback loop which is different than most of the other Z EL84 amps.
|
|
|
Post by Jim @94 Amps on Apr 2, 2008 16:01:56 GMT -7
The only split load power sections are in the RXES and SR NR. I can't remember if the Mazerati is or not, but the Stangray and GT are not.
As far as I remember the Mazerati has the same fixed bias PI as the Ghia, and they both have an interesting global feedback unique to those amps.
|
|