ArnoldC's IT coupled 300B amplifier - diyAudio
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Old 6th November 2007, 12:25 AM   #1
arnoldc is offline arnoldc  Philippines
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Default ArnoldC's IT coupled 300B amplifier

For the longest time, I wanted to make an IT coupled amplifier. Why IT coupled? Because I haven't made one yet, and I like the simplicity.

The original goal was to use a WE404A/5847 pentode driver, IT coupled to a 300B. So, I'm hitting two birds in one stone here- the use of pentode as a driver, and IT coupling.

I haveread J.C. Morrison's article in Sound Practices 14 and I was surprised to see that I actually have a pair of Raytheon 5847. So I thought of using these tubes for the driver.

A long time ago, I had a pair of IT transformers made by my local winder. I never got to use them, and still sits here in my office. Since then, I have forgotten about IT-coupled projects.

Then for the first time, I was able to make an IT-coupled PP EL34, driven by a paralleled 6SN7. It sounded very nice, but I never got to make beyond the breadboard. The IT is a Lundahl LL1660S/10mA that my friend started distributing here in the Philippines early this year.

I asked Per Lundahl, if I can use the LL1660S in SE-SE mode instead of SE-PP. To my delight, he said yes, and I arrived at a modified ALT-T configuration.

Here's the fruit of my labor over the last 4 days...


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By arnoldc

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By arnoldc

At the last minute,at had a change of mind since I have NOT tested the 5847 ever, I swapped in a WE396A in parallel, instead.

The rectifier is 5AR4 and FR107 in a Graetz bridge, through CLCLC, and there's a VR150 to regulate the driver supply going to the LL1660S. The power transformer is a Lundahl L1648, and the output transformers are James JS-6113HS. I'm operating the 300B within the output transformer current limit.

Please do not ask me for the sonic virtues of the amp yet, as I haven't smoke tested it

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Old 6th November 2007, 12:39 AM   #2
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Old 6th November 2007, 01:53 AM   #3
arnoldc is offline arnoldc  Philippines
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Thank you, thank you!
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Old 6th November 2007, 02:02 AM   #4
xaudiox is offline xaudiox  Philippines
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nice work prof!
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Old 6th November 2007, 02:30 AM   #5
arnoldc is offline arnoldc  Philippines
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Thanks!

Here's the guts before the complete wiring-

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Old 6th November 2007, 01:15 PM   #6
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Hi,

Nice!

Do you have a schematic to share?

Assume you don't have children, pets or careless adults around those trannys

ck
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Old 6th November 2007, 10:48 PM   #7
arnoldc is offline arnoldc  Philippines
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Hi Ck,

I have the schematic in Visio but allow me to finalize everything, including voltage readings, to make it easier for anyboy interested.

I do have a Shih Tzu who loves to nose around I will have a cover made for the Lundahl transformers soon

Incidentally, I just realized that the two Nichicon Muse electrolytics are in the wrong direction (polarity) , good thing to always make another round of review before powering up.
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Old 7th November 2007, 03:35 PM   #8
arnoldc is offline arnoldc  Philippines
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Finally, music!

Thanks to one of my mentor friend, who spent time with me tonight in troubleshooting the problem. We've covered all the usual suspects, checked and validated. Everything turned out right and I hav spent hours finding the problem. I was about to call it a night when I had this gutfeel to isolate a very unsuspecting component - the hum balance pot. While it gives me the proper resistance reading, it just don't work when power is applied. Geez! But that's over now.

Because it's too late, I played female vocals only - Hayley Westenra and Patricia Barber. So far, I'm impressed. The vocals are simply gorgeous, the details marvelous. The best amp I've brewed thus far, and definitely a different league compared to all my capacitor-coupled designs. I haven't played any rock or heavy metal so far, but I like it very much already.

Rock or no rock, my 300B tubes will no longer gather dust!
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Old 7th November 2007, 03:53 PM   #9
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Well done.
Welcome to the IT revolution.

What current did you decide to push through the drivers in the end. Is there any sign of high frequency roll off. Will you try it as PP, and how did the 300B SE compare to the EL34 PP amp.

Lots of questions.

Shoog
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Old 8th November 2007, 01:24 AM   #10
arnoldc is offline arnoldc  Philippines
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Hi Shoog,

Did you mean information technology? Geez, I was part of its evolution, spent 13 years with Unix from System 6 to AT&T System V R3. But now, I do Microsoft. Built my first Altair-style Intel 8008 chip based computer when I was young.

My sonic description was based on what it is right now... Single section (should be paralleled) 396A, 150V B+ off the 0D3, LED on the cathode.

My ears are not complaining about lack of top end sparkle, but I have to see it on the scope.

There is no plan to make a PP 300B.

Sonically, this SE 300B is a league above the PP EL34 with the same LL1660S.

Cheers!
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