Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Big Dan, Aug 23, 2005.
Who has Alessandro and who has Weber? Thoughts, comments, opinions welcome.
I have an allessandro. It's been rock solid for 5 years+ now. I bought it before Ted started selling his. If you select the options, Ted's will measure both plate voltage and cathode current, which is handy. You just flick a switch. The allessandro offers no such feature. In allessandro's favor, I can say that it is rock solid. I haven't owned a weber meter so I can't attest to their reliability/accuracy first hand. I have a buddy who does own one, and he was getting some strange readings on one socket. I don't mean to sway you from the weber though. If you were to have problems, they are a first class outfit. Ted and TA would fix it or send you a replacement quickly and w/o hassle.
BTW - the allessando measures true plate current, not cathode current like the weber (cathode current being plate current + screen current). Neither is better - but if you are using the info on the weber page for biasing, and have the allessandro, it's good to know. I just adjusted my VU meters (trim screws, real easy) on my allessandro to agree with the cathode current in an amp I have that has precision 1 ohm cathode resistors. Then when I use Weber's bias calculator, it's all good. That was probably more than you wanted to know ...................... Either way you'll be glad you got a bias meter. Oh, one other thing. If you don't have a multimeter ............ it's a no brainer. Buy the weber with the voltage option.
Hey Jetlag, thanks for the response. Let me say that I am probably going to get an Alessandro meter. I bought a Weber a while ago and had, let's just say, issues. I really need a meter still so I was looking at the Alessandro now. I just don't see much info on the Alessandro meters so I thought I would ask here.
I did not know about the cathode current vs. plate current thing. So you are saying that when I measure the plate current, I cannot use the simple "65%-70% of maximun disp. at idle" rule that see everywhere? How would I go about calculating the numbers with the Alessandro?
Say for example: using an EL-34 amp with 450 plate voltage, how would I determine the optimum plate current?
Using the method above, it would be 25/450x.70=.038
That means I would bias at 38 mA of cathode current. Now what about the Alessandro?
Actually the 65 - 70% figures you mention are for plate current, not cathode current. However, you can use them with the cathode current method and be assured of additional margin of safety as the tubes will actually be a bit colder than what you think.
Plate current x plate voltage = plate dissipation.
Cathode current x plate voltage = ? (something less than plate dissipation).
Keep in mind that not all of the current flowing thru the cathode also flows thru the plate, part of it also flows thru the screen. To determine true plate current you would need to subtract the screen current from the cathode current. This is not a large amount, so most people tend to ignore it and just make their calculations based as if it didn't exist. Jetlag was just pointing out that there is a difference.
Hope that helps,
Thanks for clearing that up for me!
I've had both.
Had the Alessandro for a few yrs. and then got a Weber w/ the voltage reading option. Sold the Alessandro, it's a fine piece of eqpt., but the Weber is more useful for me.