Dennis Had Inspire Amps

[Bombadil]

Originally Posted by Rosco65

My KT88 (non-triode) puts out about 5wpc using a 6V6. Wired for triode I wouldn't expect more than 2-3wpc. I would expect maybe 6-8wpc from a triode wired KT77.

Perhaps it would produce just 3 watts or so. I have seen single-ended triode 6V6 amps advertised as producing 4. But I don't know about the Inspire.

I'd love to have the equipment on hand to measure output. I have 4 amps I'd love to test.

[Rosco65]

Originally Posted by Bombadil

Perhaps it would produce just 3 watts or so. I have seen single-ended triode 6V6 amps advertised as producing 4. But I don't know about the Inspire.

I'd love to have the equipment on hand to measure output. I have 4 amps I'd love to test.

I sure that there is often a difference between advertised power vs. actual output power. There are also some designers who cane the snot out of tubes to get more power but usually at the expense of some other characteristics (such as sonics or tube life). A perfect example is the venerable 300B SET. The traditional operating points provide about 8 wpc. Some designers have gotten 10 or 12 wpc from the tube, but almost everyone else returns to the sweet spot of 8 wpc.

This (http://www.enjoythemusic.com/magazine/manufacture/1108/) link includes a table showing the relative output power for different "triodes", including the triode-wired 6V6 and EL85. Both of these tubes would give an honest 5 wpc when run in SEP, but probably less than 2 wpc when run as SET. With any triode-wired beam power tube, we can reasonably expect output power to be 40% of the pentode/tetrode output power.

Dennis has provided actual test results for different tube combinations for his KT**HO series amps ( there is an image of the results buried in this thread somewhere). In the non-triode KT amps (15w OPT Version) output power ranges from 5 wpc (5Y3 6V6) to 12 wpc (5AR4 KT88). I would expect a triode-wired version to 2 wpc to 6 wpc (maybe 8 wpc for a KT88).

[Bombadil]

I know my 17wpc KT88 Inspire drives tubes hard. I probably won't get as much tube life as will those with the standard 12wpc version. I wonder if my dissatisfaction with 6V6 tubes in it could be a result of driving them harder? They sound very forward in the midrange, grating even. I've tried three different brands and they all sound pretty much the same. Given that my amp drives tubes about 40% over typical values, I'm guessing that the 6V6s are pushing close to 7wpc - given that KT88s in the standard amp produce 12wpc and are pushed to 17 in my amp. It goes that 6V6s doing 5wpc in the standard are also going to be pushed harder in mine.

[Rosco65]

Originally Posted by Bombadil

I know my 17wpc KT88 Inspire drives tubes hard. I probably won't get as much tube life as will those with the standard 12wpc version. I wonder if my dissatisfaction with 6V6 tubes in it could be a result of driving them harder? They sound very forward in the midrange, grating even. I've tried three different brands and they all sound pretty much the same. Given that my amp drives tubes about 40% over typical values, I'm guessing that the 6V6s are pushing close to 7wpc - given that KT88s in the standard amp produce 12wpc and are pushed to 17 in my amp. It goes that 6V6s doing 5wpc in the standard are also going to be pushed harder in mine.

Musica Amantum has gone into some lengths describing the sounds of various tubes at the stock output points in his amp. IIRC he has indicated that some tubes (KT88, KT77) seem to like "hot" operating points while others prefer to run a bit more conservatively.

Dennis' current amp lineup uses the same operating points for all tubes. It occurs to me that not all tubes will be operated in their best range. I get the feeling that getting 7 wpc from 6V6's may not be the best choice. Frankly, if I wanted 7wpc from a tube with this character I would choose a 6L6 instead.

You can always send the amp to Dennis to have it "turned down" to a normal 12 wpc version. What you will end up with is an amp that is known to sound great but has the twin advantages of extra space to fit bigger capacitors (or an IIPS with tube rectification) and output transformers with the potential for better bass. I would rather give up a couple of watts for much better sound, including the improved overload characteristics of the IIPS at power limits. You could have a really nice 10 wpc KT77 amp that would sound much bigger than it is.

However, if you want the extra power of the 17 wpc version, I would recommend the PSE instead. I don't know current pricing, but at the time I bought mine (early adopter and frequent flyer, so my price may be different than today) the PSE was about 30% higher than the 17 wpc KT88HO. The PSE, even when run at 10 wpc (parallel 6V6GT with 5Y3GT) sounds far more powerful than my KT88HO with a 5AR4 and KT88's (12 wpc).

[Musica Amantem]

I believe for a given (fixed) set of design tube operating conditions, there is a normal distribution between SQ (vertical Axis) and Max plate current (horizontal axis). At the center of such distribution you get the best SQ at about the mid-range of increasing max plate currents. If the operating points set is moved to the left of that curve, the sweet spot will involve the smaller (less Max plate current) tubes, like 6L6 and even 6V6. If it goes the other way, larger tubes would be best ... It is a trade-off decision based on application practicalities (otherwise, Dennis's parts inventory would grow exponentially!)

In the Triode-strapped configuration, the KT-77, and very close by the KT-88 (slightly to the right of the center in that curve), rule, given the existing operating conditions. 6L6, to the left of that curve's center, start to be sub-optimized too. Even if one has highly revealing (i.e. sensitive) speakers, other than being more audible, 6V6's, far down to the left, for example, would still not be operating optimally.

I would suggest the Opt to tube-roll and dial-in those tube specs which favor the 17 Watt Pentode design (probably farther to the right, featuring higher max plate current). I would expect less stress on larger tubes and an improved sweet-spot for that amp's given operating points. This is merely a SQ observation, not considering practicalities or SPLs.

[Bombadil]

To my ears, in my 17wpc Inspire, both KT88s and KT120s sound great. Transparent, beautiful vocals with good (not great), well-defined bass. KT66s sound pretty good too. Haven't had a chance yet to listen to my Gold Lion KT77s, the JJ KT77s have been fairly good.

Less successful, to my ears and in my system, are 6V6, 6P3S-e, 5881, EL34, 6CA7.

[Musica Amantem]

Originally Posted by Bombadil

To my ears, in my 17wpc Inspire, both KT88s and KT120s sound great. Transparent, beautiful vocals with good (not great), well-defined bass. KT66s sound pretty good too. Haven't had a chance yet to listen to my Gold Lion KT77s, the JJ KT77s have been fairly good.

Less successful, to my ears and in my system, are 6V6, 6P3S-e, 5881, EL34, 6CA7.

Give those KT-77's a listen (let them burn-in for a while, though). If these sound anywhere near my Triode Inspire in your amp, you'll really like them. Once I dialed-in the KT-77 and KT-88 with their respective ideal rectifiers and input tubes, the KT-66 and even the 6P3S-E lost plenty of ground.

[Musica Amantem]

Still trying to decide (if at all) between Rythmik L12 and F12 SUBs, since what I have read around seems to indicate that, in smaller rooms, single 12" driver units should have enough power. Of course, the stereo effect of 2 SUBs is even better, but non-essential. The only apparent condition is to have larger than 5" drivers in the mains (my mains have single 10" Eminence drivers, so these fulfill this caveat and is the reason I'm not considering dual 8" options yet since the Eminence drivers project nice mid-bass). This would represent the first stage of a full bass sub-system build-up, spreading the investment over time.

I'm just wondering why my Velodyne, although having a single 8" driver and only 160 Watts RMS, sounds "boomy" after a certain volume level. This weekend, I'll try to stuff the front-firing port on the Velodyne to see what happens.

Another consideration is the F12 has two options: F12 and F12G, the latter a design by GR Research, which is presumably better for cross-overs above 80 Hz. Since I use the RED MOD high pass filters at 100 Hz, does this mean the 20 Hz range difference will have better extension with the F12G?

Any further orientation from Peter, Rosco65 (to complement your great original contributions under the present perspective), or anyone else with SUB experience, would be appreciated.

[Bombadil]

Just because your Velodyne has only an 8" driver and just 160 watts, does not mean it has a flat response curve from 40-100Hz, or that it has low distortion. It could have a mid-bass bump in the 60 to 80Hz region which could make it sound boomy. Or its overall THD level might climb at a particular volume level. Some subs produce muddy bass.

[nhparrot]

Originally Posted by Musica Amantem

I'm just wondering why my Velodyne, although having a single 8" driver and only 160 Watts RMS, sounds "boomy" after a certain volume level.

Have you tested the output using a SPL meter and reference tones? I use a Radio Shack SPL meter and a Rives Audio test CD to "dial in" the crossover point and volume setting on my subwoofer.