2. amps-preamps
  3. 140029-80294

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

I closed the cable and fuse thread because the trolls were making a mess of things. I hope they dont find me here.

I design Tube and Solid State power amps and preamps for Music Reference. I have a degree in Electrical Engineering, have trained my ears keenly to hear frequency response differences, distortion and pretty good at guessing SPL. Ive spent 40 years doing that as a tech, store owner, and designer.
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Perhaps someone would like to ask a question about how one designs a successfull amplifier? What determines damping factor and what damping factor does besides damping the woofer. There is an entirely different, I feel better way to look at damping and call it Regulation , which is 1/damping.

I like to tell true stories of my experience with others in this industry.

I have started a school which you can visit at http://berkeleyhifischool.com/ There you can see some of my presentations.

On YouTube go to the Music Reference channel to see how to design and build your own tube linestage. The series has over 200,000 views. You have to hit the video tab to see all.

I am not here to advertise for MR. Soon I will be making and posting more videos on YouTube. I don’t make any money off the videos, I just want to share knowledge and I hope others will share knowledge. Asking a good question is actually a display of your knowledge because you know enough to formulate a decent question.

Starting in January I plan to make these videos and post them on the HiFi school site and hosted on a new YouTube channel belonging to the school.


128x128ramtubes
ramtubes's avatar
ramtubes OP
460 posts
 
@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.
ramtubes's avatar
ramtubes OP
460 posts
 
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?
terry9
2,348 posts
 
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.


ramtubes's avatar
ramtubes OP
460 posts
 
@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.
ramtubes's avatar
ramtubes OP
460 posts
 
@terry9

Are you aware that the secondary capacitance of this transformer is 800 pf and the input capacitance of the speaker panel is many times lower? If I multiply that times turns ratio squared i get a primary load of 45 Microfarads. For the transformer alone.  Are they kidding? Thats a lot to drive. The QUAD transformers are quite good and much lower capacitance. 

I dont get these Plitrons at all. Tell me what is wrong with the QUAD transformers?

The primary of the Plitron is 0.1 ohm. How low is your dc offet?


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