2A3, 6BQ5, 6AQ5, 6V6, 6L6, EL34, KT88 are all exceptionally fine sounding output tubes and are worth your consideration. For what it is worth rugidized mini tubes are less harmonic than larger versions. With any of these tubes the quality of the iron will be a major determining factor as far as sound quality goes as will circuit and layout. Triode operation is very linear but pentode can sound very good too with great bass quality. A good EL34 amp in PP will give you a solid 30+ watts which can drive just about any speaker you want to good levels so that makes it a very versatile option. I very much like the 2A3 but single ended it does not put out a lot so you need a high efficiency speaker. above say 96 db where three watts will do a good job but in the low 90's you will need more like 30 watts plus. This is dependent upon you listening taste and the levels you like but is a reasonable guide. Your Forte are an honest 95 db efficient so you are in the middle if you don't need really loud then one of the smaller tubes in set operation (6BQ5, 6V6 or 2A3) with top quality iron will not fail to impress you. See which tubes do it for you then start to check out as many different circuits and amps as you can find. Best regards Moray James.