I'm looking for a used tube amplifier. I have my eye on some of Dennis Had's creations. His SE KT88 firebottle sometimes uses a 6DJ8 or a 6SN7 as a single input driver. His newer creations seem to go with the 6SN7 so I'm wondering if I should steer clear of the 6DJ8 as a driver?
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Input tubes for inspire amps
- Thread starter Tommy217
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6DJ8 is a great tube and was designed for high current, high frequency applications.
Lots of them at good prices. I'm partial to the Amperex Orange globe and the Bugle Boys...
Lots of them at good prices. I'm partial to the Amperex Orange globe and the Bugle Boys...
The 6SN7 and its 9-pin cousin, the 6CG7/6FQ7, are very linear. NOS octals are pricey, but there's an affordable Russian equivalent (6N8S) as well as reissues. The 6DJ8 is a useful tube, but it's not quite as linear and its high Gm isn't necessarily beneficial at line level. There are reports that some examples are microphonic.
Jack
Jack
You might find this thread interesting. Has over 7500 posts & pic's, with many by the folks that work with Dennis building his amps & speakers, etc.
isaacc7@cox.
Isaac
I have not seen the KT88 Firebottle using a 6dj8 before. To be fair, I haven’t looked at them much since I got mine. I use a *sn7 for the driver. Dennis says you can also use a 6sl7 or 6bx7 as well. In addition he makes it very easy to roll different types of output tubes by changing the rectifier. If you wanted to you could use an adapter to use the 6dj8 in the amp that uses the 6sn7. If I have today off I could try using a 4kn8 (with an external supply) with my Firebottle kt88 and see how it goes.
So it uses KT88, not sure why I called it that. It's actually an Inspire Firebottle SE stereo tube amplifier HO with an IIPS ( Infinite Impedance Power Supply ) upgrade. I found it odd that it used a tube from the 6DJ8 family and most of his creations use the 6SN7. Just wondered if I should hold out for one that has the 6NS7. Then I'm not even sure if this amp will drive my speakers, Dennis does think so, he recommended his new TriO amp. I didn't want to ask him many questions on the ebay add since I probably wouldn't buy a brand new one but he would be the one to ask about the different tube designs. I'll be running a pair of Anthony Gallo 3.5's but I'm using a Vandersteen low pass filters with 2 Vandersteen subs. So I'm thinking, just maybe this little amp will be able to handle them. I don't think full range would be a good idea.
isaacc7@cox.
Isaac
Yeah so the Firebottle kt88 uses an octal driver tube. The last one on eBay did at least as does all the other ones I’ve seen. Whether it has enough power is really down to how you listen and what you listen to. I’ve loved the sound of a SE 300b driving the 82db sensitive LS/3a. Well, in near field listening and singer-songwriter acoustic guitar type stuff at least. The Had amps do seem to punch above their weight class.
Check your DMs.
6DJ8 is a fine input tube used in many very successful designs. If you're hell bent on the 6SN7 then do that but no real reason to dismiss 6DJ8, all of the other choices in the amp and system will have a vastly more important impact on the outcome.
Well... I'm not hell bent on the 6SN7, just wondered why there was a very short production run on the 6DJ8 version. Dennis changed the design for some reason.
I believe Dennis used the 6DJ8 on the earlier builds he did and on request. It's a good driver for sure.
I have several pieces of Dennis's gear including the SET Fire Bottle. It is a really great amp and is deceptively powerful. I measured 13wpc using KT88.
The OPT's changed a bit on these, so look for one with the larger OPTs. And yes, they are very versatile when it comes to power tubes.
This is mine:
With his LP27a preamp
Pic showing the size of the OPTs
I have several pieces of Dennis's gear including the SET Fire Bottle. It is a really great amp and is deceptively powerful. I measured 13wpc using KT88.
The OPT's changed a bit on these, so look for one with the larger OPTs. And yes, they are very versatile when it comes to power tubes.
This is mine:
With his LP27a preamp
Pic showing the size of the OPTs
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isaacc7@cox.
Isaac
Yeah, either one can give great sound just different circuits. I took a look at the one that just sold on eBay. He now says you can use a solid state rectifier replacement to eke out a few more watts. I don't know if that's a good idea with the older versions though. The Inspire amps thread would have been a great place to ask but that place became a ghost town once you had to pay to use the forum. I was on it for a year or two but it isn't worth paying for now. Well, I guess it does give you a place to direct questions to Dennis and the ability to buy his stuff outside of eBay. So maybe that could be worth $25.
looneytubes
New Member
I wonder if we could get Audiokarma to host an Inspire amp forum? I have one of Dennis' KT88 Fire Bottle amps and I absolutely LOVE it. I have sold my McIntosh amp because I only use the Fire Bottle
I guess transformer winders have found a way to pack a lot more iron and copper in a much smaller package than in the past. All my SET amps use much larger iron than the ones pictured here, and even ones made by Dennis Had when he was with Cary. I know another company discussed this in another thread posted here. Those OPT's are very small and even the power tranny is small.
I hope they aren't trying to take the route that Carver did with his tube amps.
That was a bad scam perpetrated on a lot of people who trusted him. Claimed 75W/ch, but the output transformers were 15W Edcor.
Carver Crimson 275
Have the Inspire amps been independently tested? Medium power SETs and SEPs with too-small output transformers generally fall flat in the first octave.
Jack
This was toward the end of his active career. To be honest, I considered Bob Carver to be something of a genius in the '70s and '80s. He produced a number of highly innovative designs relating to both amplifiers and FM receivers. However, he was never a vacuum tube aficionado, and in fact was outspoken on this subject, dismissing tubes as inferior and obsolete. His later forays into this genre were IMO only desperate attempts to use his prior reputation to generate profit. By then, the field of solid state audio had long been dominated by Japanese and other imports. It was his last gasp. And although I never would have expected Carver to cheat his customers, I also never believed he was either sufficiently experienced or knowledgable to produce top-shelf vacuum tube audio gear.
Jack