SOVTEK EL-84 (standard grade ) - These tubes are affectionately called STOVE-TOPS, due to their low plate and screen voltage requirements. They arenít as rugged as some 84ís, but have a warm, thick, clean sound and a very focused distortion. Top to bottom they are well balanced with a very transparent mid-range response. As I stated earlier, if installed into a properly designed circuit, (ie. plates and screen voltages under 320 volts ) they will last many hours. Great Blues tone, nice sustain with moderate attack.
SOVTEK EL-84M ( Military Grade ) - Not designed for audio applications, will handle higher voltages in a poorly designed amp, but sound flabby on the low-end, with splattered distortion. Wattage is increased by use of these tubes, but at the cost of tone.
TESLA EL-84 - Strong, long lasting, and powerful tube, a drop in replacement for HI-FI amps using the rare and discontinued 7189. Increased output power will be noticed when using this tube. Its strengths are its lower mid and bass response, very punchy, but be careful of its top-end -very transient and edgy. Again when used in properly designed circuit, this tube excels in head room and balls. Great rock tone, punchy , with strong attack..
EI EL-84ís - Unfortunately these tubes are very inconsistent and prone to premature failures. I say
unfortunately because a good matched quad sounds fantastic. Copied after the Amperex 84, they
stay together when overdriven with a great dimensional sound. Their poor QA makes me shy away
from using them in my amps. Full bodied and versatile, sound much like a good 6V6.