Dennis Had Inspire Amps

[Isaacc7]

Speaking of the 807, I wonder what kind of power can be gotten out of them in SE pentode? what about a pair in parallel SE? The anode in pentode mode can take a lot of voltage thanks to the top cap. Would it give up the amazing (IMO) sound it gets in the Firebottle if it got cranked up? If Dennis ever made an amp like that I’d be sorely tempted. Being who I am I would probably request it with regular octal sockets so that I could adapt them to 807, 5b/254m, and 6gb6.

[Isaacc7]

Huh, looks like Gordon Rankin already tried a higher power 807 SE amp with mixed results. https://www.fidelity-online.de/wp-co...ractices-2.pdf

The resulting power isn’t all that much more than what we can get with the KT88 Firebottle. I am also curious if the 20lb output transformers are really necessary. The extra handful of watts requires that much of a jump? I know both Gordon and Mike were both experienced designers but I dunno, seems like the OT could be smaller and less expensive.

[Analog Addict]

Time to get started on my new build, the PSE 8417. I doubt this will ever be an official Inspire offering, since Dennis doesn't like to build commercial offerings featuring hard to source tubes, and 8417's are not just lying around everywhere.

But, I have been looking at this tube for awhile. One might consider it one of the final culminations of the tube designer's art, as it was one of the last developed power pentodes developed before germanium and silicon made tubes "obsolete".
Yes there have been newer tubes developed, like the KT-90/120/150/170, but in my mind these are mere iterations of an earlier design, and not something new and different like the 8417. And since I have a reasonable stash of 8417s, I decided to see what this tube was capable of...

I decided to reuse the Slammer's power supply, albeit upgraded to provide the B+ voltage the 8417 is capable of handling.

However, first order of business was getting the corners welded up and then prepped for cutting/powder coating...

Untitled by analog addict, on Flickr

Untitled by analog addict, on Flickr

Untitled by analog addict, on Flickr

And after a lot more sandpaper mixed with elbow grease, here's one of the welded corners ready for cutting.

Untitled by analog addict, on Flickr


However, once I had the chassis ready, I found out that Straitwire was just too busy to cut my chassis, so I was going to have to do it myself. Ugh...The job I like the least when building amps from scratch. So be it.

Next was getting the design laid out for cutting. Dennis gave me a push by getting the first couple of sockets laid out, and then I finished it out.


Untitled by analog addict, on Flickr


Untitled by analog addict, on Flickr


Untitled by analog addict, on Flickr


Untitled by analog addict, on Flickr

Here's what the topside will look like once put together.

Untitled by analog addict, on Flickr


Unfortunately, in the next five weeks, I'll be out of town for three of them, so it will be slow going for awhile.

Stay tuned.

[Analog Addict]

Originally Posted by Isaacc7

Speaking of the 807, I wonder what kind of power can be gotten out of them in SE pentode? what about a pair in parallel SE? The anode in pentode mode can take a lot of voltage thanks to the top cap. Would it give up the amazing (IMO) sound it gets in the Firebottle if it got cranked up? If Dennis ever made an amp like that I’d be sorely tempted. Being who I am I would probably request it with regular octal sockets so that I could adapt them to 807, 5b/254m, and 6gb6.

Hmmmmm....Dennis has a BIG pile o 807's lying around the shop. Wonder if he'd consider a PSE 807?

Perhaps.

If you are really interested and he isn't, I could put one together at some point, of course with Dennis' guidance...

[Isaacc7]

Originally Posted by Analog Addict

Hmmmmm....Dennis has a BIG pile o 807's lying around the shop. Wonder if he'd consider a PSE 807?

Perhaps.

If you are really interested and he isn't, I could put one together at some point, of course with Dennis' guidance...

The 807 has become one of my favorite tubes. Well, them and their “equivalents” like vt60, 6bg6, and 5b/254m. I mostly run them in push pull these days. Have been very, very impressed using c3m tubes in triode as drivers. Running the 807 in ultralinear 350v 60ma per tube.

I have gone back to the KT88 Firebottle recently. Right now I am using 6ar6 outputs with a bl63 driver. Wonderful open and warm sound with plenty of bass. You have to use an adapter with the 6ar6 but the tubes are still cheap. Remarkable considering how high a quality tube it is.