Tube Rolling - No Change in Sound

I am an inveterate tube roller and some circuits will not respond to tube changes.
I tried to cool off a highly modded ARC SP6B pre amp. It already had the reputatation of "legendary gain gone wild." You can't simply swap lower mu tubes to get a more viable midrange and travel on the volume pot. It takes 12AX7s x 6 and only Only 2 are in supposedly real meaningful gain positions.
Try as I might for example with top of the heap 5751s -some real low mu 12AU7s, those almost passed enough current to burn up my spoeaker's voice coils, the amp seemed to care less.
The only result was a change in tone with very, little if any perceptable change in gain
I know it is purely anectdotal and can't hold a candle to the concise asnalysis above. The technical answer is the cathode follower bleeds freely into a leak grid intended to dissipate and not redirect the amplified electron velocity. A very loose lowest impedance pull if you will on the the gain. The other tubes are phase splitters/inverters which have no gain function except as input tubes. That is a matter of keeping the input signal at a predertimined voltage. This is required for the rest of the pre to "hear" the signal.
Now I am going to roll some 6SN7s yes Rodmann even though I have many inluding 4 pairs of TS RPs and Ws tall and short metal bas or black. I also have a few Kentucky Radio , National Union including the gray and several black but today I think I will try TS WGTs - NIB pristine NOS. I am not sure what they will sound like a priori.

Wax, cotton swap

I had not seen that your power amp is a Krell. Indeed theb Ken Rad has a well deserved reputation for bass energy and bass energy. The JAN Phillips WGTA is a quick more transparent 6SN7 and tends to be fairly neutral to thin. I have come to the conclusion that your amp is simply overwhelming the sonic signature of your system. In essence the Krell is going to give you all the bass your speakers can make. No tube is warmer than a Ken Rad and it does not matter if it is a VT 231 a clear glass GT a black glass GT staggered or striaght plated they are either exactly the same tube or have the circuitry that maskes them sound identical. See TubeSeller's site it's a bit old but he and Len Ho agree that there is no real difference. Also check out the permanent 6SN7 thrtead on hed-fi.org

Thanks, Mechan. I don't really agree that the Krell is overwhelming my system, or that it is giving all the bass my speakers can handle. Prior to the Wyetech Opal, I had a Hovland HP 100 pre, which was very nice, but the Opal is a big step up and led to both an increase in the depth and tightness of bass. I have had similar results when swapping IC's, PC's. And as the KenRads burn in I am noticing (or at least think I am) a perceptible increase in what I would call the "naturalness" or body in the sound: vocals sound a bit more "real", instruments more true. But it is not a dramatic change from the Philips..

I may move the KenRads from the input to output stages and see if there is any difference.

Neal

I had just read that the Ken Rad was essentially the same construction as the archetype flat plate 6SN7 which is the RCA GT. Personally I find the idea understandable if you take the construction by itself. Yes they look alike but that is the extent of it otherwise they sound nothing like eachother. I have heard that a good number of 6SN7 fans find that RCA, in particular, the Grey Glass VT-231 JAN CRC a very "lush" and rich sounding tube.
I can't hear that at all from any of the RCA tubes except for one exception. The 5692 special Red Base long lived if low biased 6SN7 sub. That tube also an invention of RCA. It is often repeated that all and any 5692 that you find no matter how labeled is an RCA product, (not true). While I find it a bit to undefined to be all that great to my ears it is a well respected tube with a devout following willing to pay more for it than all other 6SN7s. The cost remains high but only in the last year or two the Sylvania "W" or it's predecessor the "A" with the JAN CHS 6SN7W metal banded basel and the Tung Sol round plate VT-231 or CTL at this juncture will cost as much or more, to buy very different sonics.
The 5692 will bring a smooth, softer sounding presentation which I attribute it's velvety fuller tones and slower decay (better timbre) but it lacks the definition and IMHO lacks the refinement of the W. The 5692 just doesn't come anywhere near the extension and slam of the Tung Sol or the W.
To be perfectly honest the humble Green letter just no coin base please Sylvania GTB has a Bing Crosby sonorous baritone equal to most of the fancy pants tubes. It is bettered by others in terms of quickness and precision Hytron, National Union- Black glass not grey, the overall fire of the W like JAB CHS WGT not WGTA but some parallel constructed boxed "T" plate Sylvania GT-As are essentially more voltage tolerant higher dissipating Ws just to confuse you. The number of possibilities are enormous but get horribly expensive if you include the CV181 from Great Britain with the Brimar 6SN7GTY made for export ECC32 or a holy grail MOV B65 pair costing about $700-800. The softer and fuller toned tubes to try are the one time king of the hill RCA Red Base the earliest being the best and high guarded from microphony which plagues them all. The Grey glass NU which you really have to hunt down, Other 5692s the Mullard CV181.
Good Luck shoot me an e-mail I can tell you who has themm if they have any. Etc. Cheers