Maybe Leaving SET for Solid State because I want bass

Push pull amps and higher power SETs usings 211 or 845s are a decent step towards more dynamics and slam without giving up much of what you like today. Just another rabbit hole to consider. Adding subs is also certainly worth a try. Cheers,

Spencer

@faustuss 

A lot to unpack here. I'll start with the SETs and 1% issue. Then cover the false statements that appear based either vindictively or just out of not really knowing what you were talking about. 

So cracking on:

The first thing is that with SETs most of the distortion is the 2nd harmonic which is mostly innocuous to the ear. I don't think there even is an SET that can do only 1% THD at full power, but even with much higher levels its pretty obvious people don't find that disturbing. 

So  the 1% thing really is obituary. Its a value chosen to reflect more modern amps. The Knight KA95 I had when I was a kid made about that much at full power. A good number of the TI class D chips in use today make about 10% at full power.

WRT your comments about the M-60 kit; it was an early one that he put together in about 1997. All of our Mk2 (which span 1996 to 2004) and Mk3 (2004 to present Mk3.3) power specs are rated at 120V not 117; that little difference in line Voltage has a large effect on a zero feedback tube amp, let alone one that has a large number of power tubes. 

As the AC line Voltage goes down, not only does the B+ go down but so does the filament Voltage, thus reducing the transconductance of the tubes. This happens across the entire circuit. The early Mk2s like the kit in question didn't have a very good CCS in the Voltage amplifier circuit so its performance changed with line Voltage in addition to the effects on the power tubes. When we introduced the cascode version of the CCS about 1998, the performance of the Voltage amplifier was maintained quite well over an AC input Voltage range from 107 to 130VAC. So I hope you are able to understand we have made improvements in the nearly 30 years since that kit was made! The Mk3.3 took that another step in that direct by going to a solid state CCS.

During testing, if one speaker terminal is held at ground, which can happen if you use a grounded signal generator and analyzer, the distortion goes up considerably as the drive to the power tubes is unbalanced. You have to make special arrangements when testing the amps on this account since the output terminals are not grounded. 

All the gain and most of the distortion in our OTLs occurs in the Voltage amplifier. It has to swing all the Voltage that is seen at the output, which is a pretty big ask. The driver and output tubes have no gain and as a result only contribute between 3 to 5% of the total distortion of the amplifier; IOW the Voltage amplifier is where roughly 95% of the distortion of the amp occurs, quite unlike most transformer coupled tube amps.

On this account if you want the distortion down the Voltage amplifier tubes must have matched sections. If that is done, and if the amp has 120V as its IEC connector, our current OTLs measure at about 0.5% THD at rated power, which is not the same as clipping power. The M-60 will clip at about 70 Watts rather than its rated 60 Watts into 8 Ohms. OTOH if no attention is paid to the input tubes the THD will likely be about 3% THD. Matching the power tubes seems to have little effect, unsurprising has they have no gain. It is important for them to be good though!

Your comments about damage to speakers, oscillation,  DC Offset and tube life are simply false. If they were true we'd not have been around for over 49 years 

Our OTLs are unconditionally stable in that the input or output signal condition or load cannot cause oscillation.

If a tube shorts, it blows the fuse by the power cord. This very simple mechanism plus making sure the amps have large enough resistors in the output section to survive tube failure is part of why the amps are so reliable. 

The DC offset generated by the amps if the amps are not set up right is quite low and any low power speaker can handle it. It is easily monitored by a VU meter on the front of the amp where the DC Offset control is as well; its easy to set. If you see it change on the VU meter, its an indication something is up with a tube since the settings tend to be very stable over months of use.

The power tubes often last well over 10,000 hours. 

 All this said, I happen to be of the opinion that tube amps are on borrowed time, which is different from saying I don't like them. But there are class D amps that are just as smooth and detailed in the mids and highs now so I wonder, if sound quality is the goal, why anyone would bother with tube amps unless they just like playing with them for fun (which is something I do).

Hegel. My H200 integrated is nice and warm. I wanted even more so I use a tube preamp and run through the Hegel's Home Theater bypass. Tube preamp SS amp. The best combo. 

@atmasphere 

Interesting your initial response is "Then cover the false statements that appear based either vindictively or just out of not really knowing what you were talking about." instead of "that a boy, nice job doing your homework". Then what is a consumer supposed to know and what do I have to be vindictive about by simply posing the question to someone in the industry who avails himself to these forums.?!

"The first thing is that with SETs most of the distortion is the 2nd harmonic which is mostly innocuous to the ear. I don't think there even is an SET that can do only 1% THD at full power, but even with much higher levels its pretty obvious people don't find that disturbing."

You find me a hobbyist who isn't familiar with this old diatribe which wasn't even the premise of my post but a much broader question regarding the validity of what the industry wants us to know. Sorry if I quoted a thirty something year old review in which your rationalization of why your product didn't meet spec but why wasn't it designed for the AC powerline voltage available at the time? Still, there is my statement - "Interesting though I wasn't able to uncover any objective test bench evaluations of your OTL amps published since 1998, Only the subjective ones from publications that don't routinely do them." when I'm sure the few remaining publications that provide test bench data are always requesting manufacturer's samples for review and I couldn't find any regarding subsequent products included in your catalog except as I mentioned the subjective reviews found in the rest of the popular print and online publications.

To further address some of the salient questions I had and your response to them, sag in AC mains voltage is a common occurrence when evaluating power amp power output measurements but seems to usually occur with high power, high current amplifiers when the tester is trying to measure output into very low impedances. Usually, the manufactures claims of full output into those loads can't be verified because of the limited amount of current available from the wall outlet (real world). Also, my concern about the DC offset in which you responded about a meter on the front panel and a control knob so it can be readily monitored and adjusted and the setting may not require tweaking for months. I don't have to adjust bias on my tube amps for years and if it's a set bias amp I don't have to think about it at all unless I notice a degradation in sound in which case I would simply replace the existing quad with a new matched one and of course I routinely have my equipment cleaned and evaluated by an experienced tech. Then there's the question of whether if loading an OTL's outputs into resistors has any proven sonic merit over having the outputs of a conventional tube amps into an output transformer which I believe is one of the aspects to the widespread attraction to the way tube amps sound. As for their days being numbered, they said that about vinyl in the 1980s.

Please don't be offended but I consider this valid exchange regarding a very pertinent issue.

Another vote for a couple of powered subs.

That's what subs are for.

That's what I added to my B&W 803 D3s.

Transformed my system.

Certainly more than any amp change.