300b lovers

..and what Lynn is not saying is that these amps address these problems.   Without going into proprietary detail, I will say that there are two separate power supplies in each amp and that every tube plate in the amp has a healthy inductance between it and the power supply that feeds it.  These things add up:)  The matching preamp also is transformer coupled and has a ridiculously overbuilt power supply.   

The 300b is incredibly extended at both frequency extremes when you can drive the heck out of it....... It is not slow and syrupy at all, but rather it has lighting transient response and stunning bass.  If driven correctly.....

Great discussion.  My current amp has 3 heater voltages so I can use 300B, 2A3, or 45s.  I've tried all 3, settled on some 2.5V 300b's because I found good tubes in stock.  

This amp is a 6SN7 driven amp so now I wonder is the 45s or even the 2A3s are easier to drive.

I'll put my 45s back in for a while (kenrads) and re-evaluate them.

Jerry

One of the really fun things about designing an amplifier from scratch (not from 1950’s schematics) is you can hear for yourself when you make a change. Reviewers can only treat these things as "black boxes", and customers can only work at the margins with cable swaps. Don and I can change topologies, power supplies, tubes, basically everything.

Every change is audible, but some are far more important than others. Driver design is right at the top of the list. That’s what makes or breaks an amplifier. I wish more designers understood this.

I shouid add there is no 1950’s or 1960’s tech in the power amp or preamp. All of the tubes were designed in the 1930’s, and the circuit is a combination of 1930’s and 21st-century tech. No relation to Golden Age tech, in other words.

Lynn,

I have a burning question that you, Don, or Ralph might be able to answer.  So you start with a new design with caps and resistors and power supplies, etc. and then you put it on the bench to test it out and of course give it a good listen.  Conventional wisdom is that caps etc take a while to run in so do you have to run in the whole design for a a while to get the true sense of it and then tinker with the component parts thereafter.... and then wait for them to run in again before making an evaluation?  I would think this would be an even more difficult process with speaker drivers... which clearly  need to loosen up.   My Spatial Triode Masters sounded awful for the first 50-100 hours but gradually came to life.  At the risk of teeing up a disputatious topic, I often wonder if it is our ears that break in or the audio components.  Breaking in speaker wire just seems silly to me, something I have never honestly experienced. Any insights would be welcome on this tangential issue. which would give us a glimpse into the design process 

Fortunately, Don and I know where the "bad actors" are, and it’s no secret. Caps. Specifically, film caps. They’re the parts that need the 10 to 50 hour run-in. I do not like this ... it suggests the plastic film is undergoing a very slow chemical change while it is being charged, and a further change when the charge is modulated by an audio signal.

But direct-coupling is a whole another can of worms. The worst is that failures in one part of the amplifier cascade through the amplifier, and can even destroy loudspeakers. This is the typical failure mode of solid-state amplifiers ... a DC servo circuit, or voltage regulator, fails, and then destroys everything that is DC-connected to it. Cap-coupling or transformer coupling limits the failure to one part of the amplifier, and limits the scope of the failure to no more than a few parts.

Also, Don and I have prior experience and expectation to guide us when we try XYZ change. Is it audible at all? Is it better or worse, or just different? I don’t know about Don, but I can hear changes in ten seconds or less, and have a better, same, or worse reaction, or sort of a mixed feeling.

The mixed feeling is a danger sign and indicates that there’s something I don’t like but can’t describe or pin down. That’s pretty common at the serious design level, by the way. You often hear or feel things that just make you uneasy, which is a sign to turn it off immediately and take a good, hard look at the circuit and see what you missed. Maybe a wiring error. Look again. Stop, think, reflect, do something else. It happens to us all.

Yes, fresh film caps often sound dull, flat, and dynamically compressed. There are often subtler colorations I describe as "glossy" or softened, a kind of over-processed Photoshop impression. You hear it a few times, and you know it immediately.

But compared to an outright circuit error, that’s nothing. Those sound much worse, grainy, shrill, shouty, almost always something very very wrong, and almost always in the high frequencies. Does it sound "electronic"? Yeah, that’s bad. Find out what’s wrong. Look hard enough and you’ll find it.