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Old 10th January 2010, 05:09 PM   #11
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Quote:
Originally Posted by Jaap View Post
So you changed your mind
Hi Jaap, no, not really. I think my last post stated I was going to stick with the original 5687 driver with the CCS on the plate (for that 2A3) and possibly play around with the idea of the D3a later.

I bought 4 James 6123HS and 2 6112HS, I used the 6112's for the 2A3 Hagtech Clarion. I also have the JEL300Bdx started too. I bought a quad of these D3a so I have plenty to play with.

So, I am sticking with my original plans, I think.......although I really don't know what they were when I first started!

It will be a couple of months before I even get around to the amp I am inquiring about here....if I ever do.

I just have read in several places about this D3a being such a great driver for the 300B, etc....but there doesn't appear to be much in terms of designs and schematics out there that I have found aside from the DRD topologies.

I will look at the links others have posted here for sure.
Jeff
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Old 10th January 2010, 08:05 PM   #12
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Quote:
Originally Posted by Shoog View Post
The biasing I have seen report of wining out against all comers in side by side preamp tests - is a cathode resistor with supplementary CCS current feed to multiply its voltage drop to an appropriate bias point.

Shoog
Hi Shoog

I would sure like to read that report - is it possible to link to it?

Cheers
Raymond
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Old 11th January 2010, 12:37 AM   #13
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Default Ok, this is what I have come up with...

First, Pauldune....I had some errors in the PM I sent you, I think I worked them out here.

This is what I have come up with so far. I dont have a circuit drawing program (yet) so I will write it out.....please tell me what you think.

First the output stage I will leave basically untouched from the JEL300B.

I will be using the 3.5K tap on the primary of the James 6123HS and supply it with a B+ of 435, give or take a few volts.

The 300B cathode resistor will be 880 to 900 and bypassed with a 100uF 160V Elna Cerafine or BG. The grid leak for the 300B will be 220K with a 1K grid stopper.

This is exactly the same as JEL's 300B so far.

For my driver stage I have come up with the following, please let me know what you think and suggestions are very welcome....

I want to use a shunt-mod for volume control with a 50K pot and a 47K pass through resistor for thesunt mod. As I understand the volume control resistances with be my "grid leak" resistor.

The D3a will be wired triode and supplied with a 160V B+ via a resistor off the main B+, I will add an additional RC filter stage here with about 50uF....all to bring my driver B+ to 160v.

The plate load will be my K&K CCS set at 20mA with a cathode resistor of 75-82R bypassed with a 470uF Cerafine or BG.

This stage will then be coupled with a 0.33 PIO Russian K40 type cap.

Thats it......did I leave anything out?

RCDaniel, that is the extent of my experimentation....whether or not it is guilded by sound scientific principals....I will let everyone else be the judge.

Thanks again,
Jeff
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Old 11th January 2010, 04:19 AM   #14
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Hi,

Quote:
Originally Posted by jmillerdoc View Post
I was wondering if anybody knew of a great 300B design that uses the D3a as the driver.
I build one for a friend that can use E810F & D3a interchangeably.

Operating point is my usual standard. The Schematic pretty much matches my 437A/300B Amp documented here:

300B-SE-Amp von Thorsten Loesch

Only difference is in the cathode of the Driver, I adjusted the cathode resistor to give me 180V/10mA with the E810F, this is not supercritical.

You can replace the anode load choke with a CCS, in that case the 22K resistor supplying the +B to the Anode Load choke becomes 2.2K.

The various original chokes are no longer available to the DIY market, but you can use alternatives.

Another easy to build this whole amplifier is what I call "simple SE" and documented as "bonus schematic" in the Manual for the Film Capacitor Universal Power Supply for diyhifisupply.com.

While using a 6SL7 there (paralleled sections) for reasons of availability, with the CCS set to 10mA and the cathode resistor adjusted you can just drop the D3a in:

Putting It All Together -- Simple 300B Maxed Out With Modules AND No Electrolytics! | Diy HiFi Supply

That Certain Something | Diy HiFi Supply

Of course, this schematic presumes that you use all the fairly expensive (but very convenient and high performance) modules from diyhifisupply.com, which of course I would not advocate though I use them myself quite extensively of course.

Ciao T
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Old 11th January 2010, 09:05 AM   #15
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Default That Certain Something

A little off topic:

"That Certain Something" is similar to what I would like to do for my first build, though will probably use a different choke-loaded driver, cathode bias on the output, and snub the power transformer B+ secondary (per John Swenson suggestions?).

Driver is not settled: ether E180F or a low mu pre (double as headphone amp) with a med mu driver for the power amp.

Apologies for the diversion - back to the topic at hand.

Cheers
Raymond
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Old 11th January 2010, 09:16 AM   #16
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I'm at work now, so I cant do much now, but i'm going to draw you a schematic this evening. I think its going to be much simpler than you expected. You cant drop the voltage to make the b+ 160v, because then the ccs has no working voltage anymore. With a appropriate heatsink the ccs does everything for you. Just choose the right current, and make shure that your ccs can handle the voltage it has to drop. (about 300v but it should be able to handle 400v(i dont know the k+k modules)) power dissipation in the CCS is then about 20ma x 300v= 6 Watt.

The CCS regulates the dropping voltage to keep the current constant at 20ma. so if the plate swings up, the dropping voltage swings down, just so that the current stays 20 ma. The cathode resistors you have chosen give you a V plate of approx. 180v. I would use the 75 ohms.
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Old 11th January 2010, 09:20 AM   #17
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Hi,

Quote:
Originally Posted by rcdaniel View Post
"That Certain Something" is similar to what I would like to do for my first build, though will probably use a different choke-loaded driver, cathode bias on the output, and snub the power transformer B+ secondary (per John Swenson suggestions?).
Then it will be quite far off the "Je Ne Sais Quoi" then.

I suggest you keep the fixed bias on the output. With a sufficiently quiet PSU and high quality caps from +B to Common this sounds unusually good (I have done it both ways often enough by now).

I'd even go fixed bias on driver stage, if it was me...

Ciao T
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Old 11th January 2010, 09:51 AM   #18
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Quote:
Originally Posted by rcdaniel View Post
Hi Shoog

I would sure like to read that report - is it possible to link to it?

Cheers
Raymond
It was a shoot out at the Netherlands triode meet I think - a number of years ago. The result was big news with those who follow things like that. Unfortunately it been a number of years ago I haven't got a link to it.
If you are interested it would be a relatively easy mod to try. The CCS can be a simple resistor from the B+ rail, and the rest is just choosing the cathode resistor.
Its not an idea that has been appropriatre for my projects which need high resistance in the cathodes to work best, so I cannot comment personally.

Cheers

Shoog
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Old 11th January 2010, 10:04 AM   #19
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Quote:
I don't think that the D3a is doing anything else than amplifying here
Hi Jaap,

It is not amplifying anything actually. The 6H30 is doing all the amplification.
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Old 11th January 2010, 11:31 AM   #20
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Pauldean,
Thanks....yes I forgot about the need for the voltage swing and the fact the CCS does all the work. I look forward to the schematic.

To everyone else, I have read about the importance of considering the power supply as an integral part of the signal path. I realize there are many ways to "skin the proverbial caat" when it comes to power supplies. I want to do some reading on the in's and out's of proper power supply design beyond the basics (I know how to use PSUD etc....) and was wondering if there are any good threads on power supplies one might suggest reading.

The 2A3 build is coming along well....I just finished the chassis (always the most time consuming part of the build for me).
Jeff
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