I was aware of the 6BQ5/EL84 compatibility but have yet to try it out. The amp is on the market. Thanks.capnjuan said:Interesting; you might want to consider a pair of current make/model JJs, THDs, or other newer EL84s; they are drop-in substitute for the 6BQ5 and the new ones are said to be pretty good. And, for what it's worth, vintage twin 6BQ5 amps - because they accept EL84s - are considered more valuable than the twin 6AQ5 version. If you're trying to sell it, good luck with your sale! CJyem said:No, the amp currently runs on two RCA 6BQ5s (the grey looking ones).