Tubeage questions

deepee99 wrote:A couple of questions from the unwashed.
1. Firstly, has anyone else tried the 3D21WB Bendix, CBS or Tung-Sol or any other 3D21WB in lieu of a KT-88?
These are all from 1950-60s, NOS, the seller(s) say that with the adapter socket, they will drop right in for a KT88. If so, how do they bias and sound? Payoffs?
All other things being equal, which is  the better-sounding OP Tube: The Kt-88/6550 series or the 6CA7/EL-34 series? And does it make sense to buy two ST-70s populated with two quads of the smaller (and earlier) EL-34s, or the ST-120 with a single quad of the bigger KT-88s?
A foursome of GEC Gold Lions fetches ~ $1,600
A good Mullard EL34 fetches about $50, so two quads of them come to $400.
Now a pair of ST-70 kits will cost quite a bit more $$ than a single ST-120 kit, for about the same power in either choice.
So for the first year or even two or much longer, when finally you replace your tubes, you'll be even. But the third time the ST-70s are re-tubed, they will beat the KT-88s price by $800 then and forever more, meaning that $800/year or whatever begins to add up against the ST-120.
So what sounds better? Four KT-88s or eight EL-34s?

Dave_in_Va wrote:In my VTA ST 70, the EL 34's sounded better than KT 88's but that's not exactly what you're asking, I guess.

deepee99 wrote:

No, Dave, that's exactly what I'm asking. Put another way, would two El-34-driven ST-70s (set to mono) sound better than a single ST-120 with KT-88s? If you're talking top-grade 1950s vintage, the smaller tubes are far less expensive than are comparable KT-88s - by order of magnitude.

deepee

Peter W. wrote:

deepee99 wrote:

No, Dave, that's exactly what I'm asking. Put another way, would two El-34-driven ST-70s (set to mono) sound better than a single ST-120 with KT-88s? If you're talking top-grade 1950s vintage, the smaller tubes are far less expensive than are comparable KT-88s - by order of magnitude.

deepee

I keep a Scott LK150 making 75 wpc using two pre-blight GE 6550/KT88s per channel. Even though it is by the standards of the day a "monster amp", it does not sound as sweet as the similar-vintage 70, either in stereo or bridged. From that single experience, I would go with two (2) Vintage 70s, bridged, over one (1) 120 using post-blight tubes.

Bridging the 70 makes its output similar to a single channel of the 150. Being who I am, I did set up the Scott with only one channel active (tubes pulled on out channel, with bias reset) and the 70 to compare head-to-head. The 70 won. Even over time. 

deepee99 wrote:Peterh, I get all that about tube-rolling. But let me ask again, are KT-88s twice as good sounding as El-34s?

deepee99 wrote:Peterh. you're way overthinking this, albeit I appreciate the reminder(s) about tube-rolling. (IMHO the only cure for tube-rolling is a good red-plate event in your own home because you've spraddle-assed the sockets and they've lost contact with a tube pin or two, and that it makes more sense to blow up $50 driver tubes instead of $400 output tubes.
Let me be less obtuse:
I want 120 watts (60 WPC) to drive my speakers to adequate SPLs. The only variable is how do I get 60 WPC?
For purposes here, I have adequate supplies of NOS mid-1950s vintage of El-34 (6CA7) output tubes, and KT-88/6550 output tubes.
Cost being no issue, the math suggests either a 4-tube ST-120 amp using four KT-88/6550s OR a pair of mono-set ST-70s, each using four El-34/6CA7s for a total of 8 tubes.
My ONLY question is, which is the most sensible choice and delivers the most realistic audio for, say, a 90dB speaker array? That's my question, ALL of  it. I don't want to start another food-fight over the merits of pre- vs. post-blight tubes. We all have our preferences and you can likely spot mine. And I don't want to waddle in to what sound, sounds best. We all manage to know, without anyone having a clue, what constitutes "better-sounding" in a tube amp once all the deficiencies of amps and tubes are adequately addressed.
Thanks for your thoughts.
-d-