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5U4G power supply to 274B
5U4G power supply to 274B
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Old 19th May 2019, 01:21 AM   #1
Peckjed is offline Peckjed
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Default 5U4G power supply to 274B

Hey All,

Any tips/suggestions on how to modify (if needed) this power supply to take a 274B rectifier instead of 5U4G. These are the 274B in question, seems similar to a 5AR4 Preferred Series 274B / 5U4G Rectifier Tubes - www.thetubestore.com

Power supply schematic: Legend - Album on Imgur

Thanks!

Jeff
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Old 19th May 2019, 02:54 AM   #2
grovergardner is offline grovergardner  United States
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You don't have to change a thing. The modern 274B is a drop-in replacement. However, it bears NO relation to the 5AR4, an indirectly-heated rectifier with a much lower internal resistance. There's no comparison.
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Old 19th May 2019, 01:52 PM   #3
Peckjed is offline Peckjed
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Originally Posted by grovergardner View Post
You don't have to change a thing. The modern 274B is a drop-in replacement. However, it bears NO relation to the 5AR4, an indirectly-heated rectifier with a much lower internal resistance. There's no comparison.
Thanks for the information. When I put my 274B in the amplifier it sparked and blew a fuse. However, with a 5u4G it works fine. That was why I was curious if something needed to be modified.
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Old 19th May 2019, 03:29 PM   #4
grovergardner is offline grovergardner  United States
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What brand of 274B did you try? It's possible that 30uF for the first cap is too high, but with a circuit only drawing about 80mA it shouldn't be that big a deal. I have a friend who uses Sophia 274B's in a pair of PP300B amplfiers and he's never had a problem.

If you can modifiy the amp, you might try 10uF after the rectifier instead of 30uF. There's no sonic penalty for this and it would be easier on the 5U4 as well.
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Old 19th May 2019, 05:57 PM   #5
jhstewart9 is offline jhstewart9  Canada
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274 gassy, end of life?
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Old 20th May 2019, 11:23 PM   #6
Peckjed is offline Peckjed
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Quote:
Originally Posted by grovergardner View Post
What brand of 274B did you try? It's possible that 30uF for the first cap is too high, but with a circuit only drawing about 80mA it shouldn't be that big a deal. I have a friend who uses Sophia 274B's in a pair of PP300B amplfiers and he's never had a problem.

If you can modifiy the amp, you might try 10uF after the rectifier instead of 30uF. There's no sonic penalty for this and it would be easier on the 5U4 as well.
They are the preferred series from the tube store (Preferred Series 274B / 5U4G Rectifier Tubes - www.thetubestore.com) so I figured they should be fine since they are similar to 5U4G. But I have another 5U4G that also sparks a bit on startup... but works.
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Old 21st May 2019, 02:30 AM   #7
grovergardner is offline grovergardner  United States
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Your rectifiers should not be arcing. That is really courting trouble. I would try reducing the first PS cap to 10uF.
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Old 21st May 2019, 01:40 PM   #8
kodabmx is offline kodabmx  Canada
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5U4G power supply to 274B
Try and get a replacement or refund from tubesstore. And in the future, tube depot has better prices and service. Tube Store is located in Canada, but prices everything in USD. His prices are outrageous IMHO.
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Old 21st May 2019, 05:41 PM   #9
HollowState is offline HollowState  United States
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Install a pair of UF1007 1K PIV soiled state diodes in series with the plates of the rectifier tube. Yea yea, I know it's sacrilege to use sand in a tube amp. But do it anyway because it works and you're not going to "hear" them. It should stop the arcing and prolong the life of those obscenely priced garbage Chinese tubes.
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Old 21st May 2019, 05:56 PM   #10
Peckjed is offline Peckjed
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Quote:
Originally Posted by HollowState View Post
Install a pair of UF1007 1K PIV soiled state diodes in series with the plates of the rectifier tube. Yea yea, I know it's sacrilege to use sand in a tube amp. But do it anyway because it works and you're not going to "hear" them. It should stop the arcing and prolong the life of those obscenely priced garbage Chinese tubes.
A lot of the other threads Iíve been looking through point to that as well. Iíve got some diodes in my amazon shopping cart currently. Do you think this would prevent the 274Bís from arcing? I know the new production ones are similar to 5U4G, but still prefer a 10uF capacitor (whereas I have a 30uF currently installed)
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