2. amps-preamps
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12ax7 12AU7 EL34 / KT 88/ 6550 upgrades for PL2

I acquired a used primaluna prologue two a month or so ago. This is my first experience with tube amp. Coming from rotel amplification I am just wowed with the tubes. The PL2 had upgraded tung sol 6550s. Nice sound. But I changed to new issue Electro Harmonix H EL34EH. Ran-in the tubes two days straight with music. Was simply blown away with soundstage and tone! Guitar riffs and blues sound gorgeous! Bass isn't too shabby either. Quite enjoyable.

Then found a little more improvement by switching 12ax7s from stock to Electro Harmonix ($10 bucks each).

The tried changing out 12AU7 with some old used tunsol 5963/12au7 (made in the USA) and was not happy. Changed back to stock.

Does anybody have any good experiences with upgrading the 12ax7/12au7 and power tubes on the PL2. I would appreciate the advise. Tube rolling is so much fun!

My speakers are quad 22L2, cd player oppo bdp 83se and analog source is MMF5 w/ MMshure ML140E.
rohitdev
rohitdev OP
18 posts
 
Jwglista - I agree with you on the 6550s sounding a bit flat and dynamically constrained. I personally like the electro-harmonix EL34 to my tung-sol 6550 reissues. What KT88s have you tried?
Now the pope 12ax7 .. .are they the same as the dutch amperex bugle boys? how would you describe the change in sound from stock? I tried swapping the stock shuguang 12au7s to NOS tungsol 5963. Didnt find any improvement. Infact I liked the stock 12AU7 better.
jwglista
206 posts
 
I've only tried the stock KT88s so far. I'd like to go for some Gold Lion KT88s eventually, but I've read that some people have reliability issues with them.

I'm not sure if the Popes are the same as the dutch amperex tubes. Adding the Popes added much more dimensionality to the sound, along with a smoother and more detailed presentation. A definite upgrade over the stock tubes, and it isn't subtle either.

What you've said about the 12au7's has me reconsidering upgrading those tubes. I was going to go for some NOS Radiotechnique 12AU7/6189, but not sure that it's going to be worth the money.
evilfij
12 posts
 
I don't have the same amp, but the gold lion KT88s sounded the same if not better than either the original RCA 6550 or Genelex GEC KT88 or original Sylvania 6550 I have tried. The gold lions are expensive ($200 a quad) and I run my amps 6-8 hours a day so I am going to try the tungsol reissues next ($110 a quad).

I also found that the original telefunken 12ax7s in my preamps sound extremely good.

The bottom line is I would go with original small tubes and reissue kt88/6550 based on my experience.
rohitdev OP
18 posts
 
yes jwglista, i am getting skeptical of the value we can find sonically in upgrading the 12au7 tubes. I have always been thinking of the reissue gold lion KT88s in favor of the shuguang kt88 z since the price is nearly half!

evilfij - I have the tungsol 6550 reissues and like them. The Electro-harmonix EL34s though are more exciting in the mids than the tungsol 6550 reissues in the primaluna prologue 2.

Currently running in the new mullard 12ax7s. They sang for an hour or so last night and already sound promising...
rohitdev OP
18 posts
 
I am loving the new mullard 12ax7s. Kevin's advice was right on. Smooth organic sound yet the bass is full and less bloated than before. Seems like the noise floor went down and there is more detail. I bet the NOS mullard cv4004 may have been better. But am satisfied for the $ / sonics value of the new mullard.
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