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Old 25th April 2014, 01:04 AM   #1
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Default RL 12T 15

Has anyone seen a design using the RL 12T 15 ? I came across a design that was based on Loftin-White, the RL 12T 15, and puportedly produced excellent results. There is a blog about it, but it has no updates for 4 years. I'd like to try and duplicate the amp that Darius built. I acquired the tubes used, but the schematic posted on the blog is hard to read.
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Old 25th April 2014, 05:53 AM   #2
disco is offline disco  Netherlands
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Is Darius not the same person ad OldEurope whom posted here?
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Old 26th April 2014, 11:08 PM   #3
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Yes, that is the link. But haven't seen any posting for 3-4 years, Any idea where he is?
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Old 3rd May 2014, 07:37 PM   #4
Sheldon is offline Sheldon  United States
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What do you find hard to read about it?

Sheldon
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Old 4th May 2014, 07:07 PM   #5
Sheldon is offline Sheldon  United States
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BTW, I've built an essential identical amp using 6SN7 and 801A: loftin white 801 amp

The only differences are some part values and that Darius's amp has a grid leak resistor on the output tube (mine has that path through the resistor string that lifts the center tap of the input filament supply). Other than that, the only extra things I see are a spark gap across the output windings, and a fuse in the HV supply.

Happy to help. It's a very nice amp.

Sheldon
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Old 5th May 2014, 10:07 PM   #6
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Not being an electrical engineer, I am not familiar with all of the symbols used, so I can make out much of it, but not all. The site is in German, and while I understand a good amount, some parts are difficult to translate. Im wondering if the russian 6h30 tube would function in place of the PC86.
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Old 6th May 2014, 04:25 PM   #7
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by Tubeguy777 View Post
Not being an electrical engineer, I am not familiar with all of the symbols used, so I can make out much of it, but not all. The site is in German, and while I understand a good amount, some parts are difficult to translate. Im wondering if the russian 6h30 tube would function in place of the PC86.
It's not straightforward, but perhaps possible. Darius's design works best when the following calculation gives a value around 4 or more: Rp/((uxRk)+Ri).
Read here: Darius Loftin White explained

Also, your sensitivity will by lower. That's not necessarily a problem as long as your source has adequate output swing. I have ideas on how to make that tube work, but haven't done the calculations. On the other hand, I think you could plug in a 6SN7, as I've used. Would only require changing a few resistor values. Somewhat higher sensitivity than 6H30, but same caveat regarding source output.

Sheldon
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Old 6th May 2014, 05:11 PM   #8
Sheldon is offline Sheldon  United States
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If you want to use a 9 pin tube, the 6CG7 is electrically equivalent to the 6SN7.
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Old 6th May 2014, 08:46 PM   #9
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Thanks for all the help and links. My interest in the 6H30 is due to its reputation as being a well constructed, very rugged and durable tube. If it can work reasonably well with the 12T15, that would be something I'd like to have a crack at.
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Old 6th May 2014, 09:03 PM   #10
Sheldon is offline Sheldon  United States
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There are many well constructed durable tubes. The 6SN7 and 6CG7 both fit that description. One advantage of Darius's design is that is has a low part number and only three active components. Components were chosen for good reasons. If you want to use the 6H30, you will need to add a current source for the input plate, or change the cathode arrangement. If you know how to do it, then by all means go for it. But until you fully understand the design and the reason various values were chosen. I'd recommend the simple approach.

Sheldon

BTW, though the design is simple, the principles behind it are not obvious. They are explained in Darius's articles.

Last edited by Sheldon; 6th May 2014 at 09:30 PM.
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