actually vtls do have a margin down to 25ma so it realy won't hurt.
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you wrote: I suspect I will loose some maximum wattage, but will the amp still be able to produce that wonderful sound I like so much?
That's exactly what I think and experienced in my
McIntosh MC 2000. I have my bias set at the lower end of the bias scale with the result that the tubes are running much cooler. I might lose a bit of high power but other than that it's ok.
In general I wouldn't say that this is an imagination but closer to truth but not to all tubes and tube components. In general I can state that higher bias current almost identically to transistors bring tubes to more stable and distortionless responce with proper tonal balance as well.
After all in our case we're discussing a device with output transformer that introduces one more variable of load complexity of primary circuit matching of which to the output tubes defines the largest effect compared to the setup of the bias current in tubes.
Okay, the lower bias level doesn't seem to be a problem as long as I run it within an acceptable range. How the other way, does it make any sense to overbias the tubes? I have other tubes which support a much higher level of biasing.
What about the other issue of biasing the tube to its max current? Will this limit or affect the sound later on when the inputs are cranked up? I suspect not. I believe other parts of the tube will handle that job, but any quick description would help.
Higher biasing implies to lower gain. Lower gain implies to less distortions follow?
On the other hand higher biasing implies to higher stress and higher temperatures and lower tube life.
In tube circuitry biasing is limited with load of the primary circuit transformer and input stage that also have bias and plate voltage limits. A simple turn of a screwdriver to increase the bias can bring you very unwanted results of experimentation. Don't play with fire lad!
Most likely the tubes you have obtained do not quite fall into the required bias to plate curve, the total ma for the circuit is 120 ma with the 4 EL-34's which as I remember from reading Manleys Book the plate voltage is around 500V on that amp and 25 ma per tube is a more reasonable idle current draw for that amp, my Quick Silver M-80's are between 120-160 ma for the quad how ever I have never pushed the amp that far into class A since to me there is no sonic benifit and rapid ageing to the out put tubes will take place, you will find the next batch of tubes you use will bias up differant again, may be less current or more depending on the batch, and match quads do not hold matching evenly anyway it just gives the tube a starting set point and we hope that each will fall some where in the guide lines and does not become a current hog down the road.