Post by howie on Oct 4, 2015 8:10:00 GMT
Obviously it's a no brainer for the self biasing Ember but for the other G1217 amps you set the bias manually.
The advice is 12V for the Starlight and 22V for the Horizon. My question is how critical are these figures-would 2-3V either side matter to the sound or the longevity of the tube, as long as it sounds alright, (as it does to me)?
Some amp manufacturers even say the tube will self bias in their amps-how does a tube do that?
When biasing my Horizon manually the bias voltage, with both biasing leds unlit, are at 20.5V for 6SN7's and 24.5V for 9 pins-it's a bit bewildering. Can anybody help or maybe guide me to a website/link that will answer such questions?
The Bias voltage for the amps is not very critical.
A reasonable exact set bias voltage will give symmetrical clipping when clipping levels are reached.
In most cases nobody will ever come near clipping levels unless playing very loud with high impedance headphones or very inefficient headphones.
So +/- 2V is no problem for Horizon but would like the Starlight and SR closer to +/-1V (when warmed up)
Self biassing in tube amps works VERY differently than in G1217 amps.
In these amps the power supply voltages are well over 200V and it really doesn't matter if the anode voltage is off by 50V or so as the voltage swing needed for audio will be relatively small in amplitude.
The self biassing in tube amps is very easy and consists of a cathode resistor.
When the tube starts working a current flows and the voltage that is created pinches off the tube itself and so it settles at a certain anode voltage (that isn't that critical)
Here the anode 'current' is selfbiassing (and thus also the voltage across the anode resistor, not the anode voltage)
For G1217 amps the anode voltage is critical because the voltage swing needs to be as high as possible and symmetric.
The 'biassing' of G1217 amps thus is NOT the same biassing as what occurs in all tube amps.
It just uses the same names.
In all tube amps the voltages AND currents are MUCH higher and thus also the consumed power.
In all tube amps the tubes operate near their maximum 'abilities'.
In G1217 amps there are very low currents and voltages and thus the tubes are in no way stressed nor will they even when the bias voltage is completely off.
In all tube amps this might cause tube failure.
In G1217 amps it is impossible to destroy a tube.
The different voltages for proper bias in Horizon are unexpected.
They should be the same voltage.
Both LED's need to go off and then turn the post slightly so the 'high' LED just barely lights up.
That should give almost the same values for both tubes.
Perhaps measure the power supply voltage with both tubes and see if in both cases the power supply voltage is stable at 48V.
Could you just explain to me how to measure the power supply voltage with both tubes to check it's a stable 48V.
I mean, where do I position the probes of my multimeter?
