Dennis Had Inspire Amps

[bwilson51]

Originally Posted by FloridaBoy

The Winged C's, all new tubes actually, will require some hours to settle in.

I am glad I took your advice and gave the Svetlana 6L6gc tubes a chance to break in.I have a pair from 1997 that has black base and I thought my amp and preamp sound was great with kt66,kt-88 and el34 tubes .The 6L6gc tubes takes the amp to the next level great bass and the top end is more detailed and a wider sound stage.I have had these tubes in my closet for at least 12 years and when one powers up it makes a little noise.I just give it a few minutes before listening and everything is fine.

[bearcity]

Originally Posted by Bombadil

I


It's a free for all.

Now that is right on the money IMO. Dennis is over in Cary doing what he loves and helping us, his Inspire family, enjoy the ride.

I suspect your 17W spec on your HO is a call out to the capacity of the OPT and not necessarily the overlay output. Having heard him disparage Ultralinear in the past though I have doubts that your amp is wire that way. Maybe worth a direct inquiry.

[Bombadil]

Originally Posted by bearcity

Now that is right on the money IMO. Dennis is over in Cary doing what he loves and helping us, his Inspire family, enjoy the ride.

I suspect your 17W spec on your HO is a call out to the capacity of the OPT and not necessarily the overlay output. Having heard him disparage Ultralinear in the past though I have doubts that your amp is wire that way. Maybe worth a direct inquiry.

It's a direct quote from Dennis. He advertised it on eBay as producing 17 wpc and confirmed it when I communicated with him via email. He even had me send him a photo of the circuitry to confirm that it hadn't been tampered with by the original owner. He said the output transformers were rated up to 20 wpc.

You can't get 17 wpc out of a single-ended KT88 in triode or pentode mode. At least as far as I can determine. Maybe there is some way to overdrive the tube in pentode mode to push it up to 17?

I still have a copy of his eBay posting, from 2016. I saw two, maybe three, of these posted and no more. He had been advertising a lot of 12 wpc KT88 HO amps before this, and then he went back to those afterward.

"FIRE-BOTTLE"
NEW HIGHER POWER
17 WATT PER CHANNEL
SINGLE-ENDED STEREO AMPLIFIER
KT-88/6550 TUBE
SINGLE-ENDED CLASS A

SPECIAL EDITION

"LATEST HO EDITION"

[Bombadil]

Here's a detailed article on another amp builder who attempted to get maximum output from a KT88 single-end amp. He ran the tube in ultralinear mode at near maximum dissipation and was able to squeeze 15 wpc out of it at 5% THD.

https://audioxpress.com/article/a-si...ower-amplifier

[Analog Addict]

I'd describe it a little differently. First off, realize that this is not your typical commercial enterprise with a board of directors and a 5 year plan. This is a journey of discovery (and rediscovery) of a particularly talented and experienced individual that we are lucky enough to be able to share. There is no plan, things happen because of a whim, coincidence or perhaps fate. Let me give you a current example.

My latest amp build is a 3 tube per channel 71A PSE. The amp sounds really nice, but since I'm running three 71As on a single cathode bias, it eats up tubes, way faster than I like. I have looked at splitting the cathodes into one per tube, but because of size and space factors, I won't be able to fit an additional 4 filament transformers under the hood. So, I asked Dennis his thoughts on what to do with the amp. He suggested that I build a PSE based on three 6SN7s per channel, producing perhaps 2 wpc. And conveniently, the 6SN7 is indirectly heated, eliminating the need for separate cathode bias circuits for each tube.

So, let's just say I build this amp. I've been looking for a place to use mercury rectifiers, not an 83 type rectifier, but a real light up blue 816 rectifier based power supply. Of course some orange VR75 regulators would provide a nice color contrast




So, let's say I do get my act together and put a schematic together with Dennis' help and build this amp. For one thing, Dennis is definitely a competitive person, so if this amp is finished and up and running, he might say it sounds good, but in the back of his mind he's thinking he can make it sound even better, or that he really likes the look of the 816's and next thing you know, he's built a 6SN7 PSE amp, or included some 816's in a project.

Of course Dennis has many sources of inspiration. But since this is really a journey of discovery and not truly a commercial money making proposition, he goes where he wants and builds what suits his fancy. So either you accept the fact that there may never be any recognizable rhyme or reason or you can find a more organized, commercial venture to follow. But where else are you going to be able to buy a piece of audio gear hand built by someone of equivalent stature for the cost that he asks?

[Bombadil]

If I had the Benjamins, I would talk to Dennis about building me a pair of KT150 PSE monoblocks. Let him decide on the best rectification and driver stage. Something that could produce up to around 28-30 wpc.

A few years ago, 28-30 wouldn't have been enough for me. I was in a much bigger place and even 100 wpc was marginal. But now I'm not even certain I need above the 15-17 wpc I have now. Smaller room and playing at lower volume levels than I used to. Even when using my little EL84 amp that produces 5 wpc at most, I was pretty satisfied with the volume levels.

But I would like having more dynamic headroom and more available power for deep bass.

Perhaps if I would sell off some of my equipment, I'd have enough from that to fund most of a new amp. I'm not good at selling. And I'm pretty happy with my current amp, so there's no pressing need.

[decooney]

Originally Posted by Bombadil

If I had the Benjamins, I would talk to Dennis about building me a pair of KT150 PSE monoblocks. Let him decide on the best rectification and driver stage. Something that could produce up to around 28-30 wpc.

A few years ago, 28-30 wouldn't have been enough for me. I was in a much bigger place and even 100 wpc was marginal. But now I'm not even certain I need above the 15-17 wpc I have now...

...But I would like having more dynamic headroom and more available power for deep bass.

When I worked with DH requesting a review of KT150 monos, a few things came to surface in our back-end-forth communication. He wanted to send them with 6550s instead and expressed concern [at that time] he felt anything "more than 17 watts" did not sound right to him, for whatever reason. Duely noted and respected. In closing, that kind of rendered the $ KT150s out of the equation, if they added no real benefit in the lower watt configuration. My Inspire Hot Rod with KT150s was nice and yet my primary 93db speakers still lacked the "dynamic headroom and more available power for deep bass" you refer to. Too laid back for my taste. Maybe running two of the Hot Rods bi-amping them with my speakers - hence doubling up on transformers might have helped some, yet it was another costly R&D experiment to guess on for my speaker requirements. Today, I know for sure KT150s truly benefit running them with extra beefy mono amps, with large right-sized transformers, specifically designed for them with lower efficiency speakers in the 87-93db sensitivity range. All the dynamic headroom, top-end, midrange, and bass you'd ever need. Plenty of drive.

.

[Analog Addict]

Don't hold your breath. Maybe Straitwire has some newer info but last I heard, the output transformers Dennis prefers max out at about 20 wpc...

[Bombadil]

I believe his PSE KT88 stereo amp produces around 20-22 wpc. It would be easy to do that without pushing the KT88s too hard in SE pentode mode. One should be able to get more out of a pair of KT150s if the amp were optimized to drive them at the higher voltages for which the KT150 was designed to handle.

My amp was optimized for KT88 and those sound really good in it. As do KT150s, even though those run a bit cool in it and don't produce any additional power. I do run other tubes in it and like some of their characteristics, but keep coming back to KT88/KT150 as the ones that sound best in it.

I wonder what Dennis could do with a design specifically for KT150, running them near their maxes and not worrying about making it so that the amp could run EL34/KT77/6L6/etc.

I do occasionally look at KT150 PP amps and think about all of that power and control, but then I talk myself out of it. I do have 125wpc and 200wpc SS amps which provide excellent bass detail and power, as well as a great soundstage. But those tube SE vocals are to die for.

I'm driving 91db speakers.

[Bombadil]

Perhaps a reason why the KT150 sounds so nice in my amp is because that tube can handle voltage and current well above what a KT88 is designed for. So if this amp pushes a KT88 to its max output, a KT150 would still be easily cruising under the same load.

There would be no gain in output wattage from the KT150, given that the circuit is the same, but it would not be running near its edge. A typical KT88 circuit had a plate voltage of 250V and plate current of 140mA. Whereas a KT150 is typically 400V and 150-180mA.

Just a thought from a guy who barely knows what he's talking about.