Dennis Had Inspire Amps

[FloridaBoy]

Originally Posted by Formerly YB-2

The Soviet era tubes were generally very well made. Their military relied on tubes as the USSR never managed to develop a solid-state manufacturing capability to support their needs. Even their latest MIG fighters, which were very capable, had tube-based electronics.

Tube can survive thermonuclear events. I was a submarine sonar man back in the day. The diesel boats I served on had tube sonar.

[FloridaBoy]

Originally Posted by BearCityUSA

While browsing I ran across some 70's & 80's vintage Soviet r-807 which, at first glance, seems compatible with western 807s. Anyone tried them? I have had pretty good luck with late Soviet era tubes and figure why not try again. They do seem a bargain.

They are good tubes. tubeman.com, a good vendor, had some that were cryo treated. There is a nice pair of RCA's on the auction site for $29 buy it now.

Bear, *I* would not chase 'rare' old production power tubes. Like TS 6550's The pickings are slim and new production has eclipsed them. I have the new production TS 6550 and it is a great tube. So is the Shuguang 6550. YMMV.

[FloridaBoy]

Originally Posted by CoGT3

Doesn't match my car, but does match the 45 SET Dennis made.



Not sure about max output but think in the mid 20's with KT88's. Not really wondered about that with my 96 dB/W speakers. Have been using the 45 SET for now with all of 1.5 W so will be a pretty big jump in power for me. 45 SET is not going anywhere, just a different flavor with more grunt with the PSE. They should compliment each other nicely.

(Car is cobalt blue metallic).

I may be out of line but take the skinny tin plated copper speaker wire challenge. I tried the WE 14 gauge. Very nice. So I ordered the Dueland version from Parts Connexion and have to twist them up. Lower power amps do not need fire hose cable. Google Jeff's Place. YMMV but you will be in for a surprise.

[Formerly YB-2]

Originally Posted by Analog Addict

I thought the reason the Russians still use a lot of tube based electronics is that they are EMP resistant....

There are many places where tubes are excellent (home stereo?), but carrying the weight for their use in combat aircraft is not one of them. If the Soviets had had the capability to use solid-state they would have done so. Our military, at least the part of it I was in, was pretty much solid-state by 1985. Would not surprise me if the Soviets sourced their military electronics from Israel these days. Strange bed-fellows.

[BearCityUSA]

Originally Posted by Analog Addict

Scott,

I have been repairing an amp on a consignment repair job that apparently was a knock off of an earlier design, and it is UL. However, Dennis absolutely hates UL designs now, describing them as the worst sort of "degenerative feedback". I found it to be a good exercise for me since this is an entirely new circuit for me, and I learned a lot from playing with it and modifying the design...Oh and it's easy enough to tell if an amp is UL. If the OPT has a third wire from the primary side that goes to the screen of a beam power tetrode or pentode output tube, it's typically an UL design....

Thanks, sometimes my memory does not let me down. Some times I dream things that seem to later be real.



This is the wiring on my KT. Looks to not be UL based on your description though it would take me some time to figure which pin on the output tubes is the screen grid. Concur?

[Analog Addict]

Originally Posted by FloridaBoy

Bear, *I* would not chase 'rare' old production power tubes. Like TS 6550's The pickings are slim and new production has eclipsed them. I have the new production TS 6550 and it is a great tube. So is the Shuguang 6550. YMMV.

If you keep your eyes open, you'll come across them. Dennis has a pair of my 6550s on loan, 3 hole old stock Tung Sols. He prefers them to the new ones. I also have a quad of grey plate no hole Tung Sols that came with a Citation II that I picked up awhile ago. Haven't restored the amp yet, but the tubes have gotten some use. And the cost of the amp, a Citation IV, a Fairchild TT with wooden tone arm and the tubes was less than the retail cost of the 4 tubes at the going rate. Fell into that deal as well.....

[Analog Addict]

Originally Posted by BearCityUSA

Thanks, sometimes my memory does not let me down. Some times I dream things that seem to later be real.



This is the wiring on my KT. Looks to not be UL based on your description though it would take me some time to figure which pin on the output tubes is the screen grid. Concur?

I can't tell for sure, but I only see two wires from the primary side which would be a B+ and a plate lead....

[o]

Bear..... the amps have been both triode and pentode over the last few years.
I believe all of the amps he has built to sell lately have been pentode (he will wire it triode by request).

[pstrisik]

Regarding the Ultralinear question, Dennis emailed the following to me back in 2014 (posted with his permission):

The Inspire single-ended pentode amplifiers are operating, beam power pentode output tubes in a fashion that the tube designers intended. These pentodes were never meant to run in what is called Ultra-Linear mode. The pentode is a higher gain vacuum tube with an additional grid called a screen grid. In order for the screen grid to act in a reinforcement mode of directing the electron flow the potential should be less positive than the plate (anode). If full voltage or more is applied to this screen/beam grid vs the plate it will start to act as the plate. This is what ultra-linear causes. Peter, keep this very important fact in mind about ultra-linear ... UL is a form of degenerative feedback. In simple words UL is a feedback method. The ac audio signal in the primary winding of the output transformer appears on the screen grid in a reverse polarity equating to a lower gain feedback high impedance signal impressed on the screen grid. I read some of these ads about amps run in UL and they state no feed-back!!! What a bunch of crap. In the Inspire SE pentode design I go a step further toward the original pentode design factor with a low impedance regulated screen-grid B+ power supply. Without a fully regulated screen supply the distortion becomes very high when the tube is pushed. In fact in my design one can run the living you know what and still have a listenable experience. Run in UL or without a regulated screen supply at a lower voltage potential than the plate you have all the reasons for discounting pentodes. Pentodes operated in a fashion that the designer of the tubes intended will yield a magnificent sound closer to the recording studio original than a triode in my opinion.. I can go on and on .... I find it so difficult to read the crap that is spewed about triode vs pentode. Either tube will yield a magnificent presentation in pure class A if designed properly. Oh, I definitely use a modest amount of global negative feedback to lower the output impedance of the amplifier. The lower output impedance will allow the low power amp control the loudspeaker drivers. Feedback implemented in a proper fashion is desirable. Speaking of feed-back ... another bunch of marketing hype when I read amps claiming no feedback. When in reality most amps do have feedback in the form of current feedback, degenerative feedback, ultra-linear feedback and local and global feedback.

I better stop before I blow a gasket ... LOL Triode directly heated single-ended class A audio amps offer a bloom in the midrange. Pentode single-ended class A amplifiers offer a full bandwidth with loudspeaker control. I might add the Inspire single-ended class A amps have bass slam and a huge sound stage.

How’s that ????????????

[Formerly YB-2]

BearCityUSA - That is a very neat build on your KT. What four (4) tubes does it use?

Do wish Dennis had a website that listed his offerings.

As far as UL, my SLI-80, a many years old Dennis design, sounds much better to my ears in Triode as opposed to UL (switch selectable).