i just looked up your speakeres and found them not to sensitive and the recommended power is 10w-100. the ouptut tubes(el84) are nice tubes that do well with the upper midrange and above.i wouldnt expect any earth shattering bass from them. the seperate monoblock amps ar highly regarded so the sa2 should sound just as good as them.i had a sa2 but i parted it out for parts but kept the output transformers to clone a couple of the ua1 or 2's someday.power output is about 15w /ch so dont be expecting to blast out the nieghbours unless you have some efficienct speakers. Now, multiply that by 2 for Stereo (well, only one bias supply).Well the sa2 is basically 2 ua1 or ua2's ( they use the same output transformers) with a built in preamp. Multiply the potentiometers by 2 for Stereo. Just like so many things, it is a tradeoff.įixed adjustable bias for a pair of push pull tubes: That means the (fixed adjustable) manual bias robs from the range of the self bias circuit (less auto adjustment effect).Ī self bias resistor that gives all of the bias has a good self adjustment range (no fixed bias circuit).Ī self bias resistor that gives only 1/2 of the bias voltage, only has 1/2 of the self bias auto range (1/2 of the bias in the fixed bias circuit). Global negative feedback can not fix some of the errors in the design and implementation of an amplifier, and this is one of them it can not fix.Ĭombination bias gives both some auto adjustment range, and some (adjustable fixed) manual bias adjustment range of the current.īut the amount of auto adjustment due to the self bias resistor is proportional to the ratio of the resistance of the self bias resistor, versus the impedance of the cathode. It shows the increased distortion at 20Hz and even at 100 Hz, when there is just a small un-balancing of the push and pull quiescent DC currents.Īnd, that graph was taken With the global negative feedback. If you have any doubts about the extra distortion caused by un-balanced DC currents, look up the very last 2 pages of the Heathkit W5 amplifier manual. In regards to power at 20Hz, nothing will ruin the distortion faster than unbalanced DC in the push and pull windings. 1dB less power of 13.69 Watts is so much quieter.ġ dB difference of continuous power will not make any difference, both will burn out 95% of all tweeters. If you need 17.22 Watts at 20kHz going to your Tweeter, then you need to use fixed bias for that pair of EL84 /6BQ5. Those large bias voltages do rob lots of B+ voltage when you use self bias, and that robs output power. It is not a large Beam Power tube, or a large Pentode, they require 30, 40, or 50V of bias. First of all, the bias voltage for EL84 / 6BQ5 is only a few volts.

Heathkit sa 2