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Unusual amps..

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#541
Steve, see?

We forgot completely about ur amp!
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I didn't, I'm still playing with Steve's circuit. Later I will post pics too prove it. I'm also sure that people with amps sporting a cathodyne PI are gonna give it a try, just to know what all the fuss is about. Am I right? SY? 😛

OK, Tubelab. After reading your post it seems the root of the problem is economics and not engineer's incompetence. Either way I spent my childhood and most of my teenager years with no love for music due to crappy sounding stereos. I had these visions of lab geeks in white uniforms messing up good sound. Those visions take some time to erase, it happens with any traumatic feelings. 😛.


An externally hosted image should be here but it was not working when we last tested it.
 
#542
My teenage years,

Were spent stripping valve amps from 78 record players and building them into wooden boxes for stereo<<they didn't look good I guess but they were the great fun..Helping friends in a local pop group get guitar amps running and building circuits from Practical wireless magazine making mixers (Vero board was a magical invention) all done on pocket money..Philips radionics kits building SW radio recievers and AMTransmitters for music arround the house..Then building good tvs from a selection of bad ones.. A wasted youth with a group of friends all doing the same kind of thing..😀 And yes it was tune by ear then and saying what we thought could be done to improve..mainly power supplies because we were learning by doing "learn as you build"..The ony source of information was the local Physics teacher..🙂

Even in the 70'-80's the kind of discussion that takes place here was impossible..You have to remember that any test equipment was an AVO 8 if you were lucky..
I think it would be fair to add that the kind of thing done in my youth could not be done now without the internet..who would you talk to where would the information come from? Forget education its preparing for the next digital revolution..Valves???why the hell would you want to build with that rubbish..The old school have gone from education🙂
I do know because I work in these areas.

Regards
M. Gregg
 
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#544
Just another thought,

Here is a vison of an electronics lab in 1976 (I was their) Tektronix scope sweep generator AVO7 a big heavy frequency counter with nixie tubes rows of plastic draws with discreet components, resistors, capacitors, transistors, some IC's mainly Cmos logic. A row of work stations with soldering irons, bench PSU and filing cabinets with drawings..all for cutting edge high speed production machinery. computer what computer you need a room and puch cards and tape reels all in a temp controlled environment. computer studies at school and LED calculators.. this was the point before sinclair..

Sorry I digress.. I must add the box of Decatron counter tubes and test rig..🙂 One other thought the cutting edge machinery electronics that had to be re calibrated every two weeks and if you sneezed by it with your meter connected would drift .5v or so..a cold weather snap and out you go again because its all out again with temp change..thermistor compensation..LOL

Regards
M. Gregg
 
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#545
Final comment nostalgia,

Ok so what could have happened to Cassiel..

Well market forces, as soon as the home computer came of age the electronics was biased to market demand..and after looking inside a friends commodor pet were cheap and nasty by comp to today. However everyone wanted one this was the way forward the home entertainment of the future the game stations Atari etc..parents bought their kids them because they were left behind at school programs like the mighty micro and BBC computer Paxolin/resin circuit board tracks peel off etc. but it didn't matter this was new age..🙂

Consumer audio..the same..HIFI was there in the background (very quiet compared to the past) I listened to a Quad non valve at the time think it was a 606 and pink triangle turn table..this made me think..I wanted the sound the price was to high at the time, so back to home electronics and BYPAK kits with tip41a transistors it was way better than run of the mill stuff, then more and more different ss amps then back to tube in 1979-80 with tannoy 611's and the story goes on..🙂

So if you want good sound either its megga bucks or make your own..nothing ever changes 😀 as I remember Sinclair had some modules you bolted onto a turn table plinth and IPL had modules as well..For the non DIY home HIFI person..😀

Regards
M. Gregg
 
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#546
Were spent stripping valve amps from 78 record players and building them into wooden boxes for stereo
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I made them into guitar amps. It started when my parents upgraded the old Magnavox mono HiFi to new fangled stereo. I cut a guitar cord in half and twisted the wires to the leads in the tone arm and my first tube guitar amp was born. It was around 1962.

In 1967 I enrolled in a technical high school vocational electronics program against the wishes of my parents. It was 3 years long and it taught vacuum tubes. I made a lot of good stuff then, some guitar amps, some HiFi, some tubes, some SS. All were loud, and some actually sounded pretty good, but I didn't know why. The only test equipment used was a Simpson 260 voltmeter and an old RCA "mystery scope".

I think it would be fair to add that the kind of thing done in my youth could not be done now without the internet..who would you talk to where would the information come from?......The ony source of information was the local Physics teacher
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We had electronics magazines, I hung out at the local Lafayette Radio Electronics store to talk with other geeks and ham radio guys. They knew how to squeeze every last milliwatt out of a tube. Trips to the local trash dump were good for some first hand knowledge and a box full of tubes and parts. There were ways to learn, it just took more effort. Now we can sit here and mentally dissect each other's designs, or we can build our own. Isn't this DIY?????
 
#547
tubelab.com said:
In the audio industry, and just about every other compettitive market, the marketing department will furnish a requirements document containing specs (electrical, mechanical, and economic). It's up to the engineering department to design to those specs using whatever tools that are needed to get the job done.

It is often the case that the specs given by the marketing department are derived by marketing research that determines what it takes to SELL a certain volume of product in a given market. It often bears NO relationship to how the product actually works.

...snip...
In the early stages of development the marketing department will survey what the competition has, and what it is believed they will have at the time of product launch.

Then they will draw up a spec sheet with better numbers and ask us to design it. Negotiations will take place until we agree on something thay we can actually design and build, AND they can sell. Sometimes the first cut from marketing defies the laws of physics and they have to be reeled back into reality.

...snip...

It is exactly the same in mass market audio and always has been. The difference is that any large consumer market can be strongly influenced by TRENDS. You want what your friend has, only better. Back to the numbers game.

...snip...
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And, then there is "Feature Creep". This is when marketing comes back after you have the prototype working and are trying to get the price within range and they decide "Customer XYZ says they would buy a zillion of you will add this feature to the design", which in reality is total BS.

When I'm lucky, I am told "we have a customer that is looking at competitor X system Y. They specifically need these features 1, 2, 3... and are installing the product in this application (whatever). We need to add a module to fill in the product line so we can compete. Look at module V and tell us what you can do."

That rare moment is described as "Wheeeeeeeeeeeeeeeeeeeeeeee!"
 
#548
Evidently in the world of marketing, "feature creep" is analogous to "scope creep" in project management. In either case, uninhibited enthusiasm can lead to veritable juggernaut. What leaps to my mind are those "boom boxes" of the '80's and early '90's that had features like shortwave radio, multiple-disc cd changers, dual cassette decks, built-in tv's, etc. Eventually this wasn't enough, so speakers with square drivers and faceplates festooned with multicolored flashing christmas tree lights soon evolved. 😀
 
#549
#550
M, it's all posted on my website, including distortion spectra and reasons why I didn't use UL. Now understand that my distortion measurements (I show the spectrum, not just a number) are real ones, not some number pulled out of the air, so while they're pretty good for a tube power amp, you can't compare them to fictitious numbers.

If you're after numbers, I've built five copies so far, with average 1W THD of 0.03%, 10W THD of 0.1%, both dominated by third harmonic. But I think a spectrum is more useful.
 
#551
SY said:
If you're after numbers, I've built five copies so far, with average 1W THD of 0.03%, 10W THD of 0.1%, both dominated by third harmonic. But I think a spectrum is more useful.
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I didn't intend to compare your figures against smoke..LOL
Just looking at the one in my previous post link..
No they seem good..I was just wondering how a mosfet zener would work by comparison to the LED bias..

You know it seems everyone has become very defensive since this thread, with a bit of luck we can get back to the "what works best thread". And put the C...p back in the closet..LOL

It was /is a genuine interest of topology and unusual circuits..I think some interesting discussion has taken place so far 🙂

I must add the Red light on your site is very pretty...how come DIY audio never got the sexy pics?..LOL

Regards
M. Gregg
 
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#554
What's the AC impedance of a MOSFET zener at the 20-50mA idle current typical of an EL84 output stage? That's the important parameter.

My wife thinks that my pix of the RLD are pretty awful. She also thinks it should put out more light. The next one I build, I'll fix that. Chrisb deserves the credit for the woodworking, I'm rather hopeless.
 
#555
SY said:
What's the AC impedance of a MOSFET zener at the 20-50mA idle current typical of an EL84 output stage? That's the important parameter.

My wife thinks that my pix of the RLD are pretty awful. She also thinks it should put out more light. The next one I build, I'll fix that. Chrisb deserves the credit for the woodworking, I'm rather hopeless.
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Well,

I think it looks great perhaps other colours would be good too..🙂

So what happens with parallel Mosfets?..Stupid question..LOL

Regards
M. Gregg
 
#556
I got the idea to stuff some LED's in the cathode circuit of a Simple P-P board. I tested a few LED's and found some flash chip LED's from a camera phone that had the lowest dynamic resistance. I wired three in series and stuck a string in the cathode circuit of each EL84. It rocked AND lit up the whole room.

There was a thread here where several of us were experimenting with constant voltage sink circuits in the cathode of output stages. My experiments ended when I blew up the screen regulator and haven't had time to look back.
 

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#557
tubelab.com said:
I got the idea to stuff some LED's in the cathode circuit of a Simple P-P board. I tested a few LED's and found some flash chip LED's from a camera phone that had the lowest dynamic resistance. I wired three in series and stuck a string in the cathode circuit of each EL84. It rocked AND lit up the whole room.

There was a thread here where several of us were experimenting with constant voltage sink circuits in the cathode of output stages. My experiments ended when I blew up the screen regulator and haven't had time to look back.
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Looks like your welding..LOL

I find it hard to believe that only LEDs can hit the spot..strange 🙂

Do you get the same charge problem as FB if you bypass the LEDs with a cap?

Regards
M. Gregg
 
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#560
Depends on the zener. These are things you have to measure to make a reasonable decision. As a reference, the AC impedance of the LED array I used in my last build is about 6 ohms. That's pretty negligible in a cathode circuit.

Noise is usually not an issue in that position- besides the high signal level (10V), the noise is common-mode.
 
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