5U4G power supply to 274B

[Peckjed]

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

 

[grovergardner]

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.

 

[Peckjed]

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.

 

[grovergardner]

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.

 

[jhstewart9]

274 gassy, end of life?

 

[Peckjed]

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.

 

[grovergardner]

Your rectifiers should not be arcing. That is really courting trouble. I would try reducing the first PS cap to 10uF.

 

[kodabmx]

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.

 

[HollowState]

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.

 

[Peckjed]

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 I’ve been looking through point to that as well. I’ve got some diodes in my amazon shopping cart currently. Do you think this would prevent the 274B’s 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)

 

[kodabmx]

Up size the SS diode to 3A part (Like HER308 or UF5408) and replace that 30uF cap with a 470uF and get less ripple

The 274B might be arcing because there isn't enough plate supply impedance. Try adding a 100R 5W resistor to each plate lead and see if the arcover stops.

 

[HollowState]

I’ve got some diodes in my amazon shopping cart currently. Do you think this would prevent the 274B’s from arcing?

They can't hurt, and will certainly help. Use the 10ufD as well. ALL 274Bs are very similar to 5U4s. Even the coveted Western Electrics, who's plates are physically closer together inside, but has no bearing on their performance.

 

[jhstewart9]

Your rectifiers should not be arcing. That is really courting trouble. I would try reducing the first PS cap to 10uF.

Think the WE Spec Sheet sez 4 microF max for their version.
5U4G a much better choice if appearance is not a consideration.

 

[Peckjed]

Think the WE Spec Sheet sez 4 microF max for their version.
5U4G a much better choice if appearance is not a consideration.

I believe you are correct. I’ll likely put the two caps on a switch so I can go back and forth between 5U4G and 274B.

 

[grovergardner]

Think the WE Spec Sheet sez 4 microF max for their version.
5U4G a much better choice if appearance is not a consideration.

Yes, but unless you're running them full tilt, 10uF shouldn't pose a problem.

 

[grovergardner]

I believe you are correct. I’ll likely put the two caps on a switch so I can go back and forth between 5U4G and 274B.

Um, I wouldn't put a switch at full B+. Just use 10uF, the 5U4's will last longer that way.

 

[Peckjed]

Um, I wouldn't put a switch at full B+. Just use 10uF, the 5U4's will last longer that way.

LOL. Good point. Idk what I was thinking.

 

[Kay Pirinha]

Up size the SS diode to 3A part (Like HER308 or UF5408) and replace that 30uF cap with a 470uF and get less ripple

The 274B might be arcing because there isn't enough plate supply impedance. Try adding a 100R 5W resistor to each plate lead and see if the arcover stops.

...and placing that SS diodes in parallel with the vacuum ones dead certainly would eliminate any arcing !
Best regards!

 

[fred76]

Yes, but unless you're running them full tilt, 10uF shouldn't pose a problem.

Hi Grover,

What about in this PSU?:

http://shop.diyhifisupply.com/wp-content/uploads/2017/11/LD-diagram.jpg

The 274A has a 10uF input cap, but (in the datasheets) it is rated for 4uF max for input cap duty.. Is it the same case here that it is not being utilized “full tilt” so it is okay?? Thanks!

 

[grovergardner]

Hi Grover,

What about in this PSU?:

http://shop.diyhifisupply.com/wp-content/uploads/2017/11/LD-diagram.jpg

The 274A has a 10uF input cap, but (in the datasheets) it is rated for 4uF max for input cap duty.. Is it the same case here that it is not being utilized “full tilt” so it is okay?? Thanks!

Actually, the datasheet specifies 4uF for max duty. This circuit draws about 80mA, about a third of the max for a 274A. In my experience 10uF here is not a problem.