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Old 15th October 2010, 01:50 PM   #1
robmil is offline robmil  United Kingdom
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Default 2A3 rectifier

Hi All

Ma good friend is using a tube preamp that uses a 2A3 for the rectifier. He would like to convert it to a silicon diode rectifier. Any ideas or does anyone have a drawing of how to do it?

Thanks

r
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Old 15th October 2010, 01:52 PM   #2
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i would want to learn how your friend manage to use 2a3 as a rectifier.
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Old 15th October 2010, 02:19 PM   #3
Doz is offline Doz  United Kingdom
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Same as western electric did with the 211? ... see here
Western Electric - Rosetta Stone for Triodes
about 3/4 of the way down the page ... don't think I'll get away with one of these in the lounge
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Old 15th October 2010, 04:52 PM   #4
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by robmil View Post
Hi All

Ma good friend is using a tube preamp that uses a 2A3 for the rectifier. He would like to convert it to a silicon diode rectifier. Any ideas or does anyone have a drawing of how to do it?

Thanks

r
Or it could in fact be an 80 or similar, I had what was obviously an 80 handed to me as a "black plate 2A3" at a show once and had a real job to convince the individual doing so that it was in fact not a 2A3..
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Old 15th October 2010, 04:52 PM   #5
Arnulf is offline Arnulf  Europe
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Originally Posted by commstech View Post
i would want to learn how your friend manage to use 2a3 as a rectifier.
As you do with any triode: connect its grid to the cathode (if it is an indirectly heated tube) or to the ground, where the filament will be referenced as well (if it is a directly heated tube) and you get a diode out of it.

@robmil: what seems to be the problem ? Remove the tube, replace it with a series connection of power resistor (to obtain same voltage drop) and a silicon rectifier diode and you're done.
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Last edited by Arnulf; 15th October 2010 at 04:56 PM. Reason: Added distinction between DH and IDH tubes and fixed a typo
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Old 15th October 2010, 05:12 PM   #6
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Originally Posted by Arnulf View Post
As you do with any triode: connect its grid to the cathode (if it is an indirectly heated tube) or to the ground, where the filament will be referenced as well (if it is a directly heated tube) and you get a diode out of it.
Technically you'll get a diode that way, but in all my years the proper way has been to connect the grid to the plate as pictured in the Western Electric schematic posted by Doz. Not to the cathode.
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Old 15th October 2010, 05:36 PM   #7
Arnulf is offline Arnulf  Europe
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But this will result in grid dissipation, and could lead to a meltdown and fireworks should remains of the grid make physical connection to cathode
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Old 15th October 2010, 05:55 PM   #8
kevinkr is offline kevinkr  United States
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But this will result in grid dissipation, and could lead to a meltdown and fireworks should remains of the grid make physical connection to cathode
The grid surface area is very small compared to the plate area and almost all of the electrons will miss the grid and proceed directly to the plate. It works fine in any application I have tried, particularly with low mu triodes which have grids with wide spacings.

Your proposed connection may theoretically be worse under high current conditions if the grid actually gets warm enough and starts to emit electrons on its own. In any event its not recommended in any tube design manual I have seen.
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Old 15th October 2010, 06:31 PM   #9
Doz is offline Doz  United Kingdom
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I have a tube compressor that has the grid of an ECC82 coupled to it's plate to rectify the audio and that fed to the screen of an EF86 in the input stage to make it compress... works rather well.
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Old 15th October 2010, 07:20 PM   #10
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Perhaps I'm showing my ignorance here, but what exactly is the point in using a 2A3 as a rectifier? I'm not trying to sound pompous here, mind you. There may very well be a legitimate reason to do so (a potentially lower voltage drop leaps to mind), and I'm hoping someone here could enlighten me...
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