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

@roberjerman

So Roger: new production tubes from our old Cold War rivals. Can the Russians really make and sell quality tubes at such low prices? A quartet of 12AX7's for $18 (shipping free!). We did that ourselves back 50-60 years ago. But that was when US tube production was in the millions for the radio/television market! Do Russian mfgr's have to compromise on material quality and less vacuum- pumping to sell at a low cost?

They are doing better and better. Sometimes I send back a whole batch but not so much lately. Low noise 12AX7 are hard to make. Where do you get 4 for $18? Im sure they are not tested for noise or microphonics. Luck of the draw like poker.

Sadly the USA makers never got the noise as low as the Europeans. However USA makers were very good at power tubes.

Vacuum pumping is not a problem, cathode coating is. They told me when I visited the EI factory. "All we know is we mix up the cathode coating in a tin pail with whatever water and let it sit overnight, its better that way. However we don't know if thats because it sits overnight or perhaps the night watchman takes a leak in the bucket."

Im not kidding and that came via Dragona, our translator, right from the head of production. I spent 10 days at that factory. Sad its gone, they were on to something and I wanted to help by offering noise testing which they could not do. I passed on their offer to make me $100,000 worth of tubes, prepaid. they were broke, Good luck seeing those.

@terry9

I see you have jumped on the bandwagon of expensive parts. I have not yet found them to be superior and they are costly and often fragile. Those resistors especially. I dont see the benefit.

As far as dialectric, i understand it well. Let me ask your a question. How much AC voltage (changing voltage) is across a coupling cap in any amplifier?

I am still curious about your falling idle current with rising temp.

How do you drive the capacitance of all those QUADS. Have you done some measurements on what the combined impedance of the whole setup is?

How do you arrange them?

There are several Russian sellers on EBay that claim to have military (OTK) grade 12AX7's made circa '80 at Saratov. The prices are astonishingly low! I am tempted to buy a quartet. If I remember right, I might have bought a quartet of 6L6's from one of these sellers a few years ago. I will have to search through my tube stockpile to verify this! I recall the boxes had the proper Cyrillic printing. Thought I'd put them in my FenderTwin Reverb!

RM

happy Thanksgiving!
RV says hello - told him I recommended your RM-200 for driving some of his speakers....appreciate the insights on MKII having the cap forming switch. I know he and Low share the DBS patent and a few others have started doing that sort of thing internal to amplifiers, preamps, etc.

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

best to you

Jim

@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.