After more testing/auditioning, I prefer the Pentas over the
Tung Sols. I find the new Tung Sols are still zingy in the highs.
The Pentas are just slightly fuller compared to the Tung Sols.

That is it for now.

Cheers

pos

positron wrote on Tue, 21 February 2023 22:45

After more testing/auditioning, I prefer the Pentas over the
Tung Sols. I find the new Tung Sols are still zingy in the highs.
The Pentas are just slightly fuller compared to the Tung Sols.

That is it for now.

Cheers

pos

I am eating some crow now. I just checked and the new Tung Sols (gift years ago) I have been using needed to be demagnetized again. The JJs not so. There is also a difference in the midrange I think I like better with the JJ KT88s.

cheers

pos

Hi, Personally I prefer the JJs. In class A amps (like all my designs) they have a solid and clean bass with good mids and nice extension on the top end. They are also really consistent and stay "biased" over a long time. I use them at about 35-36 watts dissipation (each tube A+S). For a seemingly "crisper" sound the JJ EL34s are great at about 25 watts (A+S) dissipation. But my go to now in the amps are TS KT120s running at 25 watts dissipation (A+S) into 8K load. Magical IMO. Obviously class A U/L P-P is not efficient. A good source of heat in the winter though.

Hi, I get asked all the time on the Oddblock amps as to how often the tubes should be replaced. I used the original tubes (blue glass JJ KT88s) for 12 years in class A U/L at 36 watts dissipation (A+S) and they still were sounding fine and tested good. My estimate was nearly 8000 hours. Well beyond the 2K or so they spec for. Since I switched to the KT120s in the amps I figure they will last to the next century at about 25 watts dissipation. That BTW is a sweet spot in the sound, not done to be be frugal. The preamp and drivers either NOS Phillips JAN 5751 or NOS JAN Sylvania 12SL7s will likely never need replacing. In the past 15 years I have had one fail due to an internal short but none ever tested or sounded bad. BTW I suspect the Blue JJs were probably not no lead but I could be wrong. Sometimes the socket is the issue and not the tube. I normally use Belton ones. They can be testy as they grab the tube really hard though and can make it difficult to get out. I now always use SMPS for heater power that are well filtered, isolated and closely regulated.

I've been meaning to reply to this thread for a long time, but keep forgetting. When a post is
made here, I read it, make a mental note to respond when I get time, then eventually forget 'til
the next post.

I have an Audio Note Kit 2, which uses a 6550 tube wired as a triode and run Class A. I love it,
but it did show some oddities over the years, some of which may have been due to things other
than the basic circuit.

One of which was a predisposition to draw excessive output circuit current after a tube had been
run for a few years. I use this amplifier often, so a few years means several thousand hours.
At that time, it would usually start overheating the cathode resistor. This, of course, raised
the voltage across it and its bypass capacitor. After a few years, I installed a 1/4A fuse in
series with the cathode resistor, and that was magic. When a fuse pops now, I swap both fuses
and both tubes. That makes everything very predictable.

I have noticed, though, that after moving from Tulsa to Bella Vista, the excessive current
problem seems to happen less often. Seems like we've gone from maybe every four years to
every six or maybe even longer. It just seems rarer now.

But none of that is scientific at all. I haven't measured the voltage in either place,
haven't looked at the waveform, nothing. I mean, I've seen both voltage and waveform in
both places. From time to time, I've needed to troubleshoot something and on those occasions,
I look at power sometimes. But just for a few seconds, just enough to get a reading, and no
real deep dive into what's happening. Just noting that I've got 170V peak, sine looks smooth,
nothing deeper than that. In fact, I'm surprised that Bella Vista power is "better" than Tulsa
'cause no other utility services are.

Anyway, all that was just a qualifier to show what "m working with when I talk about 6550 and
KT88 tubes in my particular setup.

For me - I have tended to really like Tung-Sol and Electro-Harmonix for new production tubes. T
hey both sound great and they both behave. They last a long time.

I also have RCA and Tung-Sol 6550 tubes that were manufactured decades ago. They're strong,
almost could be called NOS but they have been used. Just lightly. They're too precious for
me to run full-time, all the time.

I like Svetlana tubes too, but for whatever reason, I don't like 'em as much as the Tung-Sol and
Electro-Harmonix tubes. It may just be psychological, because without the Cyrillic letter on them,
they're "pretenders" to me. And these days, I'm not sure I'd want the "real thing" if it existed
anyway. So that bias may have nothing at all to do with quality.

The one that really stands out as a "bad part" for my amplifier is the JJ 6550. It's a
"snap-crackle-pop" tube for me. Many of them actually make strange noises in my Audio Note circuit
and they always fail very rapidly, like in months. Not sure what's up with that, but it has happened
more than once.

This seems to track with many of the KT88 tubes as well. I have a handful of different brands, and
I'm sure some are better than others in my application. But all of the KT88 tubes seem to fail
sooner than 6550 tubes. I'm not sure what the actual structural differences are, but KT88s don't
seem to fare as well as 6550s in my Audio Note Kit 2.