Looking for 50-100 watts of Tube Power (give or take) for my JBL 4349s

@pdreher i don’t recall if you mentioned this before, but have you swapped out the stock capacitors for something a few notches up in quality/design in your QS amps? The changes in mine and a few other members (8+) who’ve followed along have also reported surprising results back to me as well. Also, changing out the stock input/driver tubes to something much better also helped after changing out the caps first. All the sudden IC cable changes became more noticeable too. Results were the same with KT150s and KT120s in my amps at least.  

I ended up using the same Mundorf Evo Silver-Gold (non oilers) in mine, same as I had in my former Cary Audio amplifiers, now in my Quicksilver Mono 120s for two years, and quite pleased. Mike Sanders is quite content with the stock caps in some of these latest amps, and they may mate with the horns he uses, not so much in my electrostatic AMT series speakers i use for whatever reasons. The Mundorfs opened up nicely, better tone, better texture, better layering, and sound coming from just behind both of my shoulders once they formed and fully settled in, fwiw. Was just curious, Best of Luck.

@decooney While I didn't attempt to replace caps on the QS's, I did swap out the smaller tubes with ANOS Mullard CV4004's and CBS 12BH7 black plates... both of which yielded improvements over the stock tubes.  I also preferred Gold Lion KT88's to the KT150's.  I have no regrets replacing the QS's with McIntosh MC-30's, with the caveat that the 60+ year old Mac's will need more regular maintenance than the new QS's.   The QS's are rock solid dependable performers and I don't doubt they will improve with mods... but the vintage MC-30's have great synergy with my Altec's and I appreciate the nostalgia of amps that were built before I was born.

@pdreher sounds like fun. My buddy had a pair of the MC-30s refreshed and ran them for many years.  Pretty neat amps.  In my larger QS amps, I found the KT150s need the right amount of plate voltage, bias,  and transformers to run their best. Going back and forth I found I actually prefer the KT120s in my QS mono amps,, and with the right input tubes and [higher-end] caps, and proper biasing - they truly sound like different amplifiers.

I'm an old EL34 fan from my Cary days, and similar amps.  From the get-go I was trying to get the QS to sound closer to those amps and this combination has me much closer to more of a hybrid golden era sound, yet there seems to be no loss of detail as long as I'm running my Cary SLP-98 tube preamp with the right 6SN7 tubes in it.  This combo of preamp and amps really sounds good, super happy with it.  Good luck with yours, enjoy!  :)  

@decooney Couldn't agree more with running 6SN7 based preamps from Cary, deHavilland and Supratek.  

@atmasphere, thanks, I will take a look closer at Class D options. I heard your monoblocks at Axpona last year and thought they sounded great.