Dennis Had Inspire SE Amps

Magnavox EL-84 by Dennis Had. Good for around 4 watts of single ended bliss.

I own Dennis' Inspire version of this amp. Very similar but no Magnavox labeling. The OPTs are a little small for the job and it rolls off the low bass. I use a powered sub with mine and it helps a lot.
 
I own Dennis' Inspire version of this amp. Very similar but no Magnavox labeling. The OPTs are a little small for the job and it rolls off the low bass. I use a powered sub with mine and it helps a lot.

To quote Dennis Had, " since the power transformer supports the console preamp ( not used in this power amp version ) you will have plenty of reserve power transformer horse power."

He recommends 87 db speakers or higher ( mine are 98 dbs ). No bass roll off here as I bi-amp my OB's
 
There has been some discussion on these amps elsewhere on AK, but I believe they deserve attention in this forum, as they do represent a tremendous value. A bit of background, Dennis Had was the founder and president of Cary Audio. He designed several of their highly regarded products. He retired from Cary a few years ago and is now hand building his own designs out of his house. He has produced amps based on vintage Magnavox amps using EL84 power tubes, single-ended amps tuned to use 6V6, 6L6, EL34, KT88, and more - some triode, others pentode, some designed for higher output, some with two or four tubes per channel in parallel single-ended mode. He has customized amps per customer spec. He has recently redesigned his power supply to incorporate new concepts. His output transformers are hand wound and custom built to his specs.

I own two of his amps. One of his older EL84 amps (which I believe he no longer builds, perhaps per custom order?) and one of his high output (HO) amps with 20 watt output transformers. Both of them sound fabulous. Incredibly open and natural. Sounding as good or better than other single-ended amps I've heard which cost several times what he asks ... which is typically $1200 to $2000, depending upon the configuration. And as the HO amp supports 6V6, 5881, 6L6, KT66, EL34, 6CA7, KT77, 6550, KT88, KT120 and KT150 power tubes, it is great fun to roll various tubes and listen to how they affect the music.

The Audio 10 blog just published a review of one of his amps.
http://www.10audio.com/inspire_fire-bottle.htm


Not sure where to post this. I have Dennis Had's Hot Rod and LP 3.1 preamp. I have changed some of the tubes in the amp and preamp - I want to stand on the tallest mountain, tallest building or paint in sky writing a HUGE thank you to Dennis for building such amazing gear. For me it is pure emotion, rapture as I listen with tears in my eyes. Dennis is a gentlemen, an individual of high moral character and an engineering genius! and just a real good guy. A big shout-out from me to recommend to anyone anywhere to try his Inspire line of equipment and you will be more than Inspired!
 
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Ya know, I'm not sure I'm buying what gets sold as being a design that will accommodate all these different tubes in all these different positions! To be frank, it kinda takes the whole concept of what the original tube manufacturers posted in their data sheets and says: Nonsense!! I mean really? Could all those makers of tubes back then have been wrong? Just because a tube has a base and pinout that matches up with several others does NOT mean it's all interchangeable...... at least not to be operating electrically properly! These tubes all have different load lines, different operating voltages, different plate load requirements, bias levels, etc. So, just because someone says you can plug in anything from a 6V6 to a 6L6 to a KT88 to a 6550, or a 12AX to a 12AT to a 12AU to a 12Ay, what ever....that doesn't mean that the amp is now working properly! From all I've come to understand (and I freely admit that I am NOT any great expert here......but have learned enough to be 'dangerous'!!), if you take any common output tube, it's going to have a corresponding manufacturer's data sheet that will supply enough info to be able to 'design' around some pre-determined optimized criteria that will produce an amplifier with output characteristics that commonly are considered 'the best' for that tube. Change tubes, and you need to change a lot of other things in order NOT to sacrifice performance levels; ie distortion, power, and even tube longevity. So, believing this to be true, I'm going to call 'Shenanigans' on some of these claims of wide tube compatibility. Maybe in a guitar amp where 'distortion' is a desired factor! But, home audio amps have one basic thing in common, and that is the objective to be able to 'REPRODUCE' a signal source as ACCURATELY as possible. Bigger amps do this at higher power levels, but swapping around output tubes and rectifier tubes and even signal tubes, all 'outside' of the tube manufacturer's operating recommendations should, by all 'data' type evaluation, only serve to reduce an amp's performance. I don't know Dennis Had, but I do know the Cary Amps.......from as far back as maybe 30 years ago? Impressive units. But they were also built to EXTREMELY close technical data standards. I wouldn't argue at all that 'tube swapping' WILL change the way an amp sounds. But, if all you care about is what sounds good to you, then fine....do what you want. But I still say that if an amp is designed to work with a 6L6 and a 12AX7, then sticking a KT120 in there with a 12AT7 is probably going to change things for the worse if evaluated on a scope and with a Distortion Analyzer. Anyway, hats off to those who tube-roll within the realm of sticking with the same 'type' of tube but of just different brands. I think doing anything else is probably altering the performance of your amp adversely, even if it 'sounds better' to you.
 
@Wharfcreek

Don't go to the Decware forum. :)
Some of the members will put in just about any tube with the same pins and different pins don't stop them if an adapter is available. Then the funny thing to me is they will talk about how the "tube" sounds.

Won't they "sound" different in a different circuit? :idea:
 
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I wont argue that what sounds best to your own ears is a choice a person is free to make. I note that DH rather 'fools' the system some by stating that some of what indicates as being 'permissible' tube-rolling is also contingent upon installing a different rectifier, which is clearly being used to 'adjust' voltage levels to keep tubes from burning up. But lets face it, the concept of a 'Universal' amplifier is like a 'Universal' automobile. You can try to put a truck, a compact, an off-road, a luxury sedan, and a muscle car all into one vehicle, but SOMETHING is gonna suffer, if not a lot of 'somethings'! Thats why I own a pickup, a Wrangler, and a Grand Cherokee Ltd. Anyway, to each their own!
 
I wont argue that what sounds best to your own ears is a choice a person is free to make. I note that DH rather 'fools' the system some by stating that some of what indicates as being 'permissible' tube-rolling is also contingent upon installing a different rectifier, which is clearly being used to 'adjust' voltage levels to keep tubes from burning up. But lets face it, the concept of a 'Universal' amplifier is like a 'Universal' automobile. You can try to put a truck, a compact, an off-road, a luxury sedan, and a muscle car all into one vehicle, but SOMETHING is gonna suffer, if not a lot of 'somethings'! Thats why I own a pickup, a Wrangler, and a Grand Cherokee Ltd. Anyway, to each their own!

I don't disagree, but I think of it like a motorcycle that is marketed as "on and off road", it may not be great at either one, but it does both reasonably well.

My guess is many tube amp buyers don't like the idea of being tied to one or two tubes and they don't want to have several amplifiers, so these "universal" type amps that can be bought or built are appealing to them.
 
Can someone tell me how many different amps he sales. I'm pretty confused.

Mark

He builds and sells what he feels like building. He will also build custom units within a certain range of choices. Generally most of his builds fall into either the SET or SEP category, although there are a few outliers and some oddities. For example, a number of years ago, I loaned Dennis a sweep tube amp built by Micah/Bricktop of AK, and he found the concept intriguing enough to build a few "Clean Sweep" amps using I believe a 6JM6. He quickly moved on to something else. Occasionally he builds parallel versions of amps, and sometimes even quad output tubed parallel single ended mono blocks.(QMB-20)

Bottom line is he has no one to make happy except himself, and one of my "jobs" is to occasionally ask him if he is still having fun, because his wife doesn't want him going back to the stress levels of the Cary days.

As far as how the "Universal" series of amps works, I can't say that I can explain it or even understand it fully, but apparently all these beam tetrodes are close enough in design to function properly in the circuit Dennis builds for them. He does use different rectifiers to change the B+ values, say a 5Y3 for 6F6s to a 5AR4 for 6550s. I kinda look at it like something similar to the way my Hickok tests all the same family of tubes. All the settings are identical, except for the Bias and English, which mostly just change the mutual conductance reading/scale. The tester otherwise applies the same voltages to all of them. Be that as it may, he always checks all his builds on a scope with sine and square waves, and has an HP distortion analyzer when he feels like using it, but looking at the waves on the scope is usually all he needs to see. That and letting his ears test the final product...But, rather than believe me, go to his ebay feedback (radioman731) and read the reviews of his gear. I personally have sold off most of the McIntosh gear that's come through my hands, since the gear that Dennis builds, or has helped me build sounds better IMO

Bottom line I try not to ask Dennis too many specific questions, since I don't want him to feel like I'm trying to pry away his ideas or anything. We've been friends for over a decade, ever since he was building amps on his kitchen table during his Cary non compete period, and I must be doing something right, because, other than his employee Tony/Straitwire, I'm the only person I know of that has a key to his shop.....
 
Thanks to AA who introduced me to Dennis and got to visit with him and pick up an amp today. An experience and a story to go along with the single ended inspire 12 watt amp. I am letting it reside at AAs house until I can sneak it past the guards at home. Then he’ll “lend” it to me to listen to for an extended period. Trying out a new strategy. All kidding aside what a thrill to hear the little 4 wpc tubes run the new klh speakers he’s using which are around 85ish dB. Dennis suggested the 7c5 with loctal adapter but the rectifier needs to be 5u4 or similar. I liked my mullard el34 xf1 sound the best on this amp today even beating the 6550 black plates I brought.
 
I love my Inspire Sweet 807 amp! Dennis was very nice and I appreciate his work. Wife loves the amp too. I also have a Cary Audio SLA-70MkII EL34 amp, a Cayin MT12N EL84 based amp and a Musical Paradise MP-301 Mk3 which uses 6L6s. Been a music lover for decades. The Sweet 807 is my favorite. It’s on all the time and I’m proud to own it.
 

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