Does anyone care to ask an amplifier designer a technical question? My door is open.

@unreceivedogma

Why would triode sound better than pentode?

Why woukd my Altec Lansing 604Cs be better for my Julius Futterman OTL3s At 16 ohms rather than 8 ohms?

And, with regard to the great interconnect debate: do you know of any testing done that approaches that of scientific blind testing that shows that any given wire, if made out of a certain material, and wound in a certain way, and shielded in a certain way, will cause electrons to move in one manner as opposed to another that can be explained as doing so and that because of that movement can be explained as yielding sonic performance that is measurably and quantifiably superior, or even just different?

Good stuff, lets go.  Triodes have inherently low output impedance and one can make a nice amp with little or no feedback and still get good performance in the areas that matter: distortion, output regulation being the most dear.

Pentodes have high output impedance and something must be done to get this down by using feedback. Pentodes became popular because they produce more power per watt of tube. For instance a single 6L6 can produce 6-8 watts single ended but 100 watts per pair push pull, in pentode. Perhaps only 20 in PP triode.

The problem with triodes is saturation voltage pure and simple.

All OTL amps like high impedance because they have lots of voltage but limited current. Since current is the limit use the forumla

Power = current squared x impedance. The amplifier max current is the same for both speakers but 16 ohms gives you twice the power of 8. 

Some cables intentionally modify the frequency response and act as filters. MIT is famous for that. Some cable makers, like those liquid metal guys, have made up a whole story of fake science to sell their wares. Some makers freeze their cables, treat them with RF from a  Tesla Coil, yada, yada, yada.  I think you can tell I dont think much or cable makers, especially the really expensive ones. 

The whole idea of tuning a system with cables seems rather weak to me. Harry Pearson was big on cables but he was an idiot. Since I brought him up, my favorite quote about HP, which he said to me in person as he leaned over his Corvette at Sea Cliff is... "Audio is a Drug and I'm the Audio Pusher".. I think that pretty well describes Harry.

RM - what starter book on basic electronics / circuit s would you recommend ?

This one, price varies widely. Its a good text. I got one for $5.

https://www.amazon.com/Analog-Electronics-Devices-Circuits-Techniques/dp/0314045538

@twoleftears 

But a popular US-based, US-manufactured, relatively inexpensive, tube integrated did hum, not a lot, from *both* the transformers and through the speakers, enough that when combined the hum could be heard from listening chair when music fell silent

.

Does the maker publish a hum level in his specs?  With input shorted any more than 0.5 mV hum is not good. Needs to be even lower with sensitive speakers, close listening, quiet room. 

I know one US maker whose limit was 2.0 Mv. That is 12 dB more hum than my limit. 

I think it wouldnt matter where you put that amp, it just has inherent hum. Many people make the mistake of thinking that all products that reach the market are good products. This is not the case. Would you care to tell us what amplifier this was?

@desktopguy

Wish I could hear your more recent designs, because based on the RM-9s, they must be very very good. 

I like my new stuff, especially the RM-10. For those who have difficult loads, play loud and need power the RM-200 is designed precisely to do that. 

The 9 is a fine amp, excellent potted transformers, UL, Triode for you . Lots of work to make. They are starting to bring more money on the used market so dont let them go for under 3,000 each. With the triode switches even more. We only made a few like that.

I hope to get a few more amps out this coming year now that I am getting more help around the shop.

@chubaka   What are rails and what to they do?

Good question. In a Solid state amp there are generally equal positive and negative supplies centered around ground. A 100 watt/8 ohm amp will typically have 50 Volts plus and minus supplies. We call those the rails. It is where we draw the current to send, via the output transistors. to the speaker. The rail voltage will determine the power of the amplifier. 75 volt rails will give you 200 watts and 100 volt rails 400 watts.

Rails were not much talked about until the advent of the SS power amps that were direct coupled to the speaker. In action the positive rail pushes the speaker cone out while the negative rail pulls it in. Again the output transistors determine how much which determines what the speaker reproduces. 

In a tube amp we have several power supplies of different voltages and currents. We call the main high voltage B+, a term that goes back to early 1900s radio. A tube amp may also have a negative bias supply, filament supply, driver supply, lots of supplies in tube amps.