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

@quincy

I have always wondered if vacuum tube technology was abandoned prematurely (for solid state), and never fully exploited to its full potential?

Vacuum tubes were not abandoned but slowly pushed aside.  However the majority of reciever manyfacturers like Fisher, Sherwood, Marantz, Pioneer, Kenwood, Heath, Knight and Lafayette all went to SS sooner than they should have. Of that list I would say only Marantz made good on the change-over in that their early SS gear. Their early SS gear is quite good where the other early SS gear was quite bad. Kudos to Sid Smith who did a very good job to make the Marantz 7T sound as the 7C. However the current value of each does not reflect this because tubes are favored. Both 7s are quite good.

Other early SS designers were Dawson Hadley of Marantz, Jim Bongorino of SAE then GAS, Quatre was horrible, Bob Carver offered power and value but not good sound. Crown was ok, Mac Intosh made some great Autoformer SS amps (see my link via my profile)

In the early ARC preamps up to and including the SP-6 Bill J stole the Marantz 7 circuit topology, added a very unrelaible, poorly regulated power supply. Bill Johnson did nothing I find interesting and just made things worse in every way as time went on. CJ, I'm sorry, never impressed me. Two Economists do not make an EE. Getting them to talk about circuits is a non conversation. Their amps are pretty classic circuits. Its not that you have anything bad but frankly a Marantz 8 is hard to beat. Really really hard to beat. I cant even say I beat it with the RM-9 but I did give more power. I don't want to over do it but Sid Smith was a far better engineer than any of his contemporaries. A lovely man. I met and interviewed both him and Saul Marantz. Perhaps I should publish the tapes. The tube HK Citation amps have some serious flaws. 

Who else shall we talk about? The RM-1 was way ahead of its time and I would love to have it reviewed if anyone wants to review legacy products. It is the first preamp to use the 6DJ8, is DC coupled, No output capacitor, response down to 0.1 HZ. Sadly ended by the folding of Beveridge ESLs. I have considered re-introducing just the line stage to sent to John Atkinson. He has never measured a line stage that does what the RM-1 does. Pardon my enthusiasm, but its really special.

If you want to give me a list of companies for a yes/no I would be happy to go down it. Some of the no’s will be no, no, no. like Counterpoint who rightly went bankrup. Sometimes the world takes care of itself. Counterpoint was a group of nasty people making a horrible product.

In short, some companies made a good transition some not. Current tube amps have some interesting ideas but none that really impress me.

@tomic601

My question is what tube testers are you recommending at sane portable prices..

The B&K Dynajet series is fine and still under $100 or less on eBay. The 601 is the one I have. Although I have the big Hickok I find it heavy and slow to set up. ALL you need is an emission tester, not a transconductance tester.

I hope to release a curve tracer/tube tester for around $1000 that will do far more than the Hickok standard. It will connect to your computer, draw graphs, match up tubes and measure a whole bunch of things I have found to be important.

I have bought a set of 4 Gold Lion (Russian) KT-66's for use in my pair of Heath W5's. $35 a tube! Originals sell for $200+ a tube (UK). They sure do look real nice! I still have the original US Tungsol 5881's in use. I wonder if the Russian ones can stand up long-term to the plate and screen voltages in the W5's

How high is the plate voltage? I didnt think the W5 ran the tubes hard? The Russian KT66s are fine and the Chinese looked good to me. Lifetime will be an issue compared to the NOS Genelex.

Originals are expensive due to supply / demand and how high someone will go.

You know the 5881 is a small 6L6 and neither has the plate area of a KT66. Are you having any problem with tube life? What do you think you get out of a pair before the silver gettering is all gone?

Jumped on the bandwagon? No - Shanghaied. Didn't want to be convinced, but the two-alternative forced choice paradigm left me no choice. Like when your optometrist says, "Better or worse? Better of worse?". Easy to design a single-blind experiment. Did so with resistors and caps. Results were clear with some components always preferred: air-gap and vacuum caps, nude Vishay resistors.

A justly famous person's apparent preference, a species of Caddock resistor, had large minimum orders, and so was not part of the test. His other apparent preference, teflon, always scored highly.

Agreed, not much AC - but conversely, not much distortion via dielectric absorption is required to degrade a small signal. 

Confirming idle current falling monotonically with time. Can't post the schematic because it's not mine and it's proprietary. Sorry. Hope you understand, even though it's poor payment for your generous help.

Each Quad has its own mono block. Two Quads facing ahead, and two Quads at one radian angles, facing in. A bit like one of Walker's experiments. Think of two sides of a hexagon on the left, mirror image on the right. And two at the back of the room, attenuated, but important.

@terry9 

Each Quad has its own mono block. Two Quads facing ahead, and two Quads at one radian angles, facing in. A bit like one of Walker's experiments. Think of two sides of a hexagon on the left, mirror image on the right. And two at the back of the room, attenuated, but important.

Its ok, ive seen plenty of SS amps. The negative temp coefficient is interesting. 

You sure have a lot of stuff there. It would still like to know what kind of capacitance you are driving at 10Khz and up. 

As to the capacitor question. In the passband there is 0 Volts of signal across the cap. 

I'm still in the Polypropylene camp. Best thing for the money. Remember any part I buy is 5 x cost to the final buyer. So I cant buy too many $50 caps expensive resistors. I also appreciate manufacturers who make relaible parts. I have found CJ, Jensen, and others to fail. There is no reason for a coupling cap to fail in this day. The problem with premium caps it the people make them do not have the years of experience that the old timers have.

While I could make an amp with all premium parts, sell it for a lot more, I just dont find anything special about these parts. I would only do it to reach into the buyers pocket.