This kind of follows on from PAGs posting last night - slow, that's me
Firstly, a big thanks to Si and family for putting up with me in the middle of a bank holiday weekend - bringing a few tunes was the least I could offer in return, mate !
Thanks for your time and sharing the knowledge .
As you the reader may be aware, I recently acquired a Tube Technology Unisis valve amp via the dreaded flea-bay. Whilst sounding very tasty, overall sound was really very dark, with bass seeming quite excessive as I got it settled in and got over the initial 'glow' - definite signs of bass bloom, to the extent that I needed to swap speakers from my Castle Conway IIs to my less bass-heavy Rega Jura's. Next step included 'socking' the ports to bring listening to acceptable bass levels in my little room.
Then early last week, one valve had a little hissy fit, went purple and started to get stinky . Needless to say, off switch operated very quickly - fortunately I was only a foot away at the time.
I had already decided a new set of valves was called for. So, last week the full complement arrived - 8 x EL84s, 4 x 12AX7's and 2 x 5751's. Replacement across the board was with Electro-Harmonix valves (big up to Tube Town Germany - super prompt and very good pricing at c.£60 for EL84s + 12AX7s - 5751gold E-Hs coming off e-bay very promply as well ).
As this amp requires biasing of the EL84s (in pairs) from underneath , I felt a bit intimidated so opted for asking PAG as a previous owner of this amp to lend a hand (literally). Must admit it is a bit scary seeing the amp powered up whilst standing on its side and having to have hands in where you know 500V is running around . I am very glad I opted for help on this - bravura is all well and good, however I am pretty sure I would have bollixed things doing this on my own with only the manual to guide me .
So, what we dicovered - the valves in place were well past their best and biasing was somewhat low!!! [Standard setting for this amp is -17V - biasing was found to be -13.6V iirc].
In went the new valves without hesitation and biasing reset to -15V, to allow for burn-in and settling - apparently should see the bias settle at/near -17V after the 20 hour run-in.
What a difference!
Bass bloom gone! Sound tightened up overall and much crisper than previously. Appreciating that this was all through PAGs (unfamiliar to me) very tasty Audio Physics.
As a base comparison, also ran Si's own TT Unisis Mk2 - sound patently similar although his tubes were obviously settled in with bass in place.
Right, well made up with the improvement, but really felt the full test would be in situ in my own system (couldn't wait to test at home).
After a very pleasant visit with a very hospitable family, back on the road to check at home.
First up the Rega Jura's.
YES! Improvement remains improvement
Sound is crisper and cleaner than before. Bass definitely reduced tremendously, in fact I would say it is in reality a bass-light sound at the moment. So first thing, out came the smelly old socks :lmao:. The difference in sound quality after switching valves is truly apparent. Given that there is a burn-in period of some 20 hours here during which time the bass will improve, I am guite happy to let it bed in with time.
Next up, putting the Conway's in circuit and seeing what's what. I will post an update for those interested (if any.......)
I suppose another possibility in due course is one I would never previously have considered...small tweaks in bais setting to change sound (although that is not something I will be rushing into :gag
Thanks once again to Si and family for a pleasant day - it even made braving those rainy motorways worthwhile :lmao: