Amplifier Power tubes - important to sound?

I’ve always found power tubes more important to shaping the sound in ways that are meaningful to me. Small tubes can also be important to be sure, but a lot of times it’s an initial "wow!" impression, then over time I either tire of that variant or just want to hear a different flavor. I listen loud (more strain on power tubes), so perhaps that explains my findings.

With power tubes, my initial impressions tend to stick. The change from a KT88 to KT120 is especially significant in amps where I’ve tried this swap. Anyways, what’s your tube amp that has 16 freaking KT88 slots to replace with a non-existent Siemens 6550? (I know op won’t answer) To be fair, if the Siemens 6550 did exist, I’d prefer it over JJ.

I actually have a pair of VAC Master 300 that use 16 KT88 (plus 8 6SN7), and even with auto bias it’s a kind of a PITA to swap. The KT120 sound great here, too.

@darkblacksmoke

The VAC amps are amazing. I also have an older statement 450S (no iQ) for my smaller 2nd system. Of all a system’s components - the big VAC power amps were by far my most fruitful "splurge". For every other component slot, I’ve found cheaper items that yield similar or at least "close" results to my splurge-level items (of course a system’s components must synergize) - this includes the VAC preamp and phono. But I don’t know how to replace the big VAC amps - they’re wonderful. I particularly love them with Tung-Sol KT120.

As for the stock tubes you found - Kevin is not trying to be a broker of NOS tubes. His magic is in the voicing of components. I’ve done the KT120 swap and also prefer some of my old 6SN7 in V1, but for the most part these units sound awesome stock. I’m familiar with his choice of EH 6922 Gold and Shuguang 12AX7B (which are long OOP - he has a large stock). I think these sound very good, despite not being chic or expensive. I’ve got a large collection of NOS, and sometimes still choose Kevin’s 12AX7B for phono slots. Not familiar with the Gold Dragon 6922 (Shuguang?) - I thought it’s been a long time since VAC shipped any Gold Dragons. Of my vintage/NOS 6922, those tubes have been a huge pain in the ass for going noisy and various other gremlins - even sourced from reputable tube dealers. Just had a Brent Jesse Mazda 7308 go noisy on me, and before that an Amperex 7308 had its glass tube crumble out of the blue. I’m about to give the EH 6922 another go. I don’t blame Kevin for no longer supplying NOS. He used to favor Amperex 8416 when they were cheap and easy to find, btw.

Edit: I didn't know the Master has a "II" revision now, neat. Do you happen to know what that entails?

I don’t believe you. The 807 uses a top anode cap and a seven pin socket. It is not swappable with octal power tubes. I had some in my tube collection.

I thought that was odd too. Maybe a weird typo?

I’ve used a Williamson amplifier (pair of Heathkit W5) with Gold Lion (Russia) KT66 and it was very "powerful" sounding with strong bass, good "slam", and plump full mids. The same amp, fitted with vintage GE 7581A (near KT66), sounded more airy, spacious and articulate with a gorgeous midrange - but leaner in bass.

Sadly, power tube rolling becomes quite painful in amps using more than a quad. Vintage/NOS is pretty much out of the question. BUT once you get so many push-pull pairs in parallel - that’s where the real magic and beauty of tube power lies for me. On just one push-pull pair per side, I will certainly prefer the tonality of EL34, 6L6GC / KT66 over KT88 - at least until I run out of power,

Curious, I read herein that the feedback level related to the amplifier is important to consider for purposes of evaluating whether it really makes much of a difference to tube roll power tubes. Anyone know why that would be?

Further, I am biamping with mc 901 monos and since the solid state part of it handles the bass drivers maybe power tubes are not that important since it appears it impacts the bass area more so.

But since I love spending so much money on everything audio even the slightest change might be worth considering. Maybe power tubes would impact the mid driver.

@emergingsoul 

Agree with @dogearedaudio - feedback does not free us from the impact of tube rolling on sound. Lessens it some - but never completely gone, in tube land!

Even if those MC 901 push bass frequencies with the SS section (really nice looking amps, btw) - most of the "music" lives in the midrange, and the sonic fingerprints of your components and tube choices will sum up and reveal themselves here. It's not just a matter of raw power; amps each have their own "sound" even when loafing  - but they'll certainly strain and sound more colored when pushed hard, so having more headroom is an asset. 

@immatthewj 

It's not just about producing max power IMO. The parallelization smooths out imperfections in each PP pair, and more importantly gives headroom at lower levels. There is an effortless sense of power, finesse and grip with my larger Master / Statement level VAC amps compared to the Signature 200iQ (to be fair there are other improvements too, besides more PP pairs & power). On a good day, the 200iQ sounded wonderful. On other days, the treble seemed a little aggressive. On others, the bass sounded either a bit lean or too loose / bloated. Even on a "bad" day, the Master and Statement amps will outperform the 200iQ's best days. 

@darkblacksmoke 
Lovely, entertaining read! Agree / relate with most of that - though I am a young kid in this hobby (mid 40s) and only caught the tail end of analog tech (film, tape, CRTs) in my youth. Thanks for clarifying on the Signature II. Also don't forgot when they went from those artfully bent square and "D" getters to stamped out halos. Though the structure itself probably has no impact on sound, the earlier square / D getter variants always sound better. Also RIP triple micas and smoked glass :( 

I have the rogue Apollo monoblocks which use 12 Kt88

I have 3 sets of tubes. Golden lion Electro Harmonix Kt90 and Kt120.

The 120 are colored in my application.

The kt90 and sharper and firm the gold lion I give the nod to good luck

@hiend2 I’ve also used all 3 of those tubes in Apollos. Totally agree with your assessment there. EH KT90 were bright / sharp. Gold Lion KT88 was the best, and my fiend with Zeus (now he has my Apollo Darks) agreed too. The effect of power tube rolling is typically VERY clear! Tung-Sol 7581A sucked by the way. Now I feel stupid for trying it, and I still have 12 of the damn things. 

KT120 was my favorite with all of VAC’s amps, though. You could definitely say it’s a bit colored, but the way it turns out in the VAC amps really works for me lol. I can see why most prefer the GL KT88 there too. But I simply can’t understand how anyone liked KT150 in these amps.

Do power tubes affect the full freq spectrum or is it more focused on below 250 hz?

Of course it is a full spectrum impact. Who is claiming otherwise, and how? If I cared most about below 250Hz, I’d run solid state.

Maybe I should’ve said do they impact the lower frequencies more? You own interesting speakers

@emergingsoul

Ok, I see. If you are jumping between types like from KT88 to KT90 / 120 / 150 then YES, it will usually have more notable impact on bass response - but still contributes a LOT in midrange and HF too. If you are just swapping sub-brands of New Sensor tubes of the same type (e.g. KT88: Gold Lion, Mullard, EH) then the changes are a bit more subtle overall, and not disproportionately noticeable in bass. Swapping NOS versus new production (of the same type) is probably between the 2 - I don’t have experience doing this with KT88, but some with EL34.

I've heard that before - various incarnations of "rolling tubes in this slot won't affect the sound", because "they're cathode followers with 100% feedback" etc. Still haven't met a slot that doesn't affect the sound. It's directly in the audio path.

You can have components that are "voiced" for the specific tubes it ships with. Sometimes components have a strong voicing on their own. In these cases, tube rolling may not readily yield satisfying results - but it WILL affect the sound. Always. Now is it a useful endeavor; a good use of time & money? That's for you to decide.

It's not surprising some manufacturers would discourage rolling. When you owe warranty support on these heavy, complex amps - do you really want users rolling them with power tubes willy-nilly, from unknown sources and questionable matching? Plus they may sell their own branded (labeled) replacement tubes, at healthy markup.