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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 13 Apr 2016, 07:12 
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Joined: 26 May 2009, 23:07
Posts: 6
WoW. Thankyou.
I did suspect there was a gaping hole in my knowledge somewhere here.
And you just started to fill it in.
Yeah I have been scratching my head over this I can tell you.
I could not understand how so many from you to JC morrison and JELabs could have it so wrong.
Is there anywhere you recommend to do more reading to be able to understand this better?
For example how do you calculate roughly, just how much extra voltage you can expect to be
compensated for ? How did you know there would be enough?

cheers ,
Paul.


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PostPosted: 13 Apr 2016, 16:30 
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Paul wrote:
Is there anywhere you recommend to do more reading to be able to understand this better?
That depends...

If you've had a class in calculus then I highly recommend "Theory and Application of Electron Tubes" by Herbert Reich available here "http://www.tubebooks.org/Books/reich.pdf" (37Mb so don't just click; download the linked file).

If you haven't had a class in calculus then I recommend "Principles of Electron Tubes" by Herbert Reich available here "http://www.tubebooks.org/Books/reich_principles.pdf" (18Mb so don't just click; download the linked file).

There is lots of good stuff available at "http://www.tubebooks.org/technical_books_online.htm". Poke around and you'll find some other good stuff.

I also strongly recommend Richard Kuehnel's books "Vacuum Tube Circuit Design: Guitar Amplifier Preamps" and "Vacuum Tube Circuit Design: Guitar Amplifier Power Amps" available here "http://www.amazon.com/Richard-Kuehnel/e/B002M91X94/ref=dp_byline_cont_book_1" as of this writing. You can also get them from Antique Electronics Supply. These are very down to earth but do tend to focus on Guitar amplifiers rather than simple music reproduction. But I still have copies on my bookshelf.

I hope this helps.

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PostPosted: 13 Apr 2016, 19:39 
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Joined: 26 May 2009, 23:07
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Thanks Matt,
those links are a rich source. A bit more than I need to understand it though.
v=L di / dt is enough. drop the current quickly and create an opposing emf that adds
to the anode volts,,, will do me :) .
What amazes me is how hopeless morgan jones is, 2nd edition of his book anyway.
I think he initially creates the impression of building knowledge from the ground up,
but then you find him assuming buckets of knowledge. Back emf from inductors being
an example in point. I didn't find any mention of it in his single ended triode stuff.

chs,
Paul.


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PostPosted: 13 Apr 2016, 20:02 
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Paul wrote:
What amazes me is how hopeless morgan jones is, ...
I have the third edition of his "Valve Amplifiers" book and lets just say that I have issues with it. There is some interesting information on various configurations but that's about as far as it goes. I would never recommend any of his books. There are much better resources available.

Actually I think that "Principles of Electron Tubes" should be pretty much required reading for anyone that wants to build tube amplifiers. It lays out virtually everything you need to know to truly understand what your building.

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PostPosted: 14 Apr 2016, 00:35 
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I am thinking of building a 300B amp. I can post pics and progress here.
But it won't be anywhere near as pretty as Marks! ;) just a pre warning.
He's into sound and looks. I only care about the sound, so I tend to lack
some polish on my projects :) . Anyway we'll see if I get the time etc yet...


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PostPosted: 14 Apr 2016, 03:00 
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Paul wrote:
I am thinking of building a 300B amp. I can post pics and progress here.
But it won't be anywhere near as pretty as Marks! ;) just a pre warning.
He's into sound and looks. I only care about the sound, so I tend to lack
some polish on my projects :) . Anyway we'll see if I get the time etc yet...


I think you would be amazed how little extra effort and thought is required to make an amp look as good as it should sound. There are plenty of examples of great looking DIY builds to get some ideas. A raw Al chassis with open frame trannies and full length pot shafts sticking out is not a pretty sight and I fell it dumps down the art. A mate makes my timber bases and a spray can colours my Al top plates. That's as hard as it gets.

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PostPosted: 14 Apr 2016, 04:44 
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mwhouston wrote:

A raw Al chassis with open frame trannies and full length pot shafts sticking out is not a pretty sight and I fell it dumps down the art.


its a free country brother,
beauty is in the ear and eye of the beholder ;)


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PostPosted: 15 Apr 2016, 11:15 
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Location: MB, Canada
Paul wrote:
mwhouston wrote:

A raw Al chassis with open frame trannies and full length pot shafts sticking out is not a pretty sight and I fell it dumps down the art.


its a free country brother,
beauty is in the ear and eye of the beholder ;)


The eye of the beholder indeed.
I personally find the aluminum look to be rather visually appealing.. In my books you can have a refined look while keeping things kind of raw.
I've gone so far as to anodize my aluminum chassis, but even still I like a clear anodizing because I like the look of brushed aluminum that comes through.


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PostPosted: 30 Nov 2016, 19:33 
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I have enjoyed the Silver Dragon ever since I swapped it back for a much less expensive pair of 6EM7 monoblocks. But a month or so back I re-sold the amp to a fellow audio club member who has a number of my creations including one of my T4 Class Ds. This beautifull big amp has gone to a good home and sounds extremely nice driving some Harbeth 40.2s.

After all these years of having the amp, and all the effort over nine months collecting high-end parts and building it and swearing I would never sell it, I really don't miss it. I thought I would. I guess when it is time to let go, then it is really time.

I'm currently quite distracted with Class D builds and a new tube project. That maybe why I'm not missing the amp. I'm sure my friend wouldn't mind me dropping in for a listen now and then if I'm really missing it. Time to move on.

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PostPosted: 11 Apr 2018, 22:20 
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Suncalc wrote:
Well actually not quite. What I am suggesting is two independent windings (or transformers) with 6.3V 1.2A (or greater) windings.

Let me explain. In a DHT the noise induced on the signal by the heater voltage is equal in magnitude to that due to B+ supply ripple. This is why DHTs are specifically designed for DC heaters. It is possible to use a balanced AC heater but the noise immunity for such will always be suspect. As such, given the requirements for high fidelity, a set of DC heaters are a must.

The requirements for the heaters are being driven by ripple (noise) and channel separation. The target ripple requirement for the B+ supply is .003% or -90dBv. Since the heater ripple is induced directly on top of the bias voltage this means that the requirement for heater ripple is...

Vr = 71v * (10 ^ (-90/20) ) = 2.25mV

Due to the incredibly low effective load presented by the heaters, 4.17Ω, acquiring this level of filtering on a high current circuit with just passive filtering will be virtually impossible. As such I am strongly recommending the use of LT1085 low dropout regulators to supply the heater circuits. These regulators give almost 70dB of ripple rejection by themselves and I believe that by using them the 2.25mV total ripple will be achievable.

This is the circuit I am proposing for each 300B heater. Please note that the heater circuit is not grounded in any way. Each heater supply must float approximately 71v above ground and will be ac coupled to ground via the driver stage cathode coupling capacitor.
Attachment:
Heater_circuit.jpg

I know that this is a violation of your normal approach to building amps (Retro-Thermonic) but I believe that in this case the use of these regulators is warranted. The LT1085 is a low dropout regulator with excellent startup characteristics that will handle the difficult job of initial heating of the cold filament. In addition, the snubbing of the heaters with a 0.1µf tantalum might also be a good idea.

The other requirement driving the heater supply design is the channel separation requirement. In order to preserve the soundstage of the amp, a channel separation of at least 70dB is required. One of the reasons that 300B amps do so well as mono-blocks is that the channel separation is guaranteed because the only connection between the amps is via the very low impedance mains. If both heater circuits are in the same box then either two magnetically isolated transformers are required or the DC circuits needs significant buffering to prevent crosstalk. The reason I recommended the dual secondary Hammond is because with each regulator offering 70dB of ripple rejection, the channel separation via conduction is guaranteed to be 140dB plus another 10dB or so for the coupling loss in the transformer. Thus preserving a deep and wide soundstage.

I hope this sheds some more light on the heater supply design. It's not final as there are a couple of prototyping experiments I would like to try, but this should give you some insight into my thinking on the matter.


Hello, would the LT1085 to regulate the voltage for the 300b heaters still be the most practicable approach given the passage of time. I think i may need to use something similar.

thanks.

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