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In Reply to: RE: Phase inverter tube choice question posted by fredtr on May 14, 2020 at 09:11:56
The sound improved (not subtly either) by changing the 12Au7 out of the center position and putting in a more linear 12BH7. The only reason I haven't changed the outer two positions is because Bob said it made no difference. Only until recently have "I" noticed - it DOES.
I was never a big fan of the 12AU7. WHY I bought them, I don't know???
Honestly, if this doesn't improve the sound while using the EL34 output tubes, I'm selling the amp. I bought this amp to use those tubes. It sounds WONDERFUL with the KT66's, but unfortunately I didn't want a KT66 type amp.
My experience with KT66's was with Quad II amps. I found some original Genelex KT66's and wasn't impressed. I tried some 6l6gc black plates and the difference was significant.
If you do replace your amp, what are you thinking of buying?
I am MORE than happy using my Sherwood S-5000 (EL84M Russian tubes).
I ran a dedicated input line directly into the driver tube and bypassed the entire preamp section. The 7199 driver is now a Amperex 7643 gold pin driver tube. The entire unit has been fully restored/upgraded by Mike Samra.
There is nothing like the sound of a good EL84. It's amazing and I always loved it.
My summer time amp is a fully restored Marantz 250M. To me it just ain't getting much better than these two amps.
So what am I getting if I sell the VTA - who knows???? But I know I don't need or really want anything else right now.
I agree with you about EL84 amps. I have some Heathkit UA2's I really like and a couple of EL84 integrated amps. Unfortunately my speakers do better with more power. What speakers do you like with the EL84's?
Believe it or not, I'm using 85db Zaph Audio SR71's with NO problems.
I got the EH 12BH7 tubes yesterday and tried them in the splitter positions. I really don't understand how ANYONE can say, they don't make an impact. I popped them in and HOLY COW. The upper bass/lower midrange was solid as a rock! Great tone. I'm only hoping that the upper treble relaxes a little more as the tubes break in. But in short they are much better balanced than the 12AU7's and offer more "feeling" to the sound.
I'll start a new post with the results.
Thanks for asking
The EH 12BH7 tubes will settle. If I recall correctly Bob Latino stated that they handle voltage swings far better than the 12AU7. My ST-70 is currently using an NOS Tung Sol 12AU7 in the center, the two EH 12BH7 on the outboard and four Psvane EL34s for power. A Sovtek rectifier as well. It's a sweet sounding amp that is the heart and soul and as it plays tunes as well as being used for the TV it is on most of the time and is very stable.
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