5U4G power supply to 274B

[Peckjed]

Originally Posted by grovergardner

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

Sounds like a 10uF would probably work with a 274B and 5U4. I may be being sent some Mundorf 3.9uF for free, it seems like these would work well for the 274B... would it also work for the 5U4?

[grovergardner]

Originally Posted by Peckjed

Sounds like a 10uF would probably work with a 274B and 5U4. I may be being sent some Mundorf 3.9uF for free, it seems like these would work well for the 274B... would it also work for the 5U4?

Sure, if they're rated for 600+ vdc. Check your B+ afterward, though, it may be lower than you want. And you may get an increase in ripple noise.

[fred76]

Originally Posted by grovergardner

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.

Thanks Grover.. The 5R4G is close in ratings and might be a good substitute too for the PSU I linked. Peckjed’s circuit looks like it could work with the 5R4G(Y) too if input cap is reduced to 10uF..

[grovergardner]

Originally Posted by fred76

Thanks Grover.. The 5R4G is close in ratings and might be a good substitute too for the PSU I linked. Peckjed’s circuit looks like it could work with the 5R4G(Y) too if input cap is reduced to 10uF..

The 5R4 is a nice tube.

[TonyTecson]

what is the dc resistance of the windings feeding the plates of the rectifier? if lower than 100 ohms you can series connect 3 watt resistors to make the dc resistance to about 100 ohms per side, even somewhat more can help....

[Peckjed]

I know this was from a while ago. I installed the 10uF cap in place of the 30uF and the diodes on the rectifier. No issues with the rectifier anymore! However, I am noticing a hum from the choke that’s seems to be transferring to a 60hz hum on the speakers. Could lowering the 30uF to 10uF have caused this?

[kodabmx]

No. That hum (if any) would be 120Hz. Are you sure it's not 120Hz?

60Hz usually is caused by ground loops/heater hum. If you short the inputs to ground, does the hum go away? If yes, it's a ground loop.
Does the hum go away as soon as you switch the amp off? If yes, this means it's coming from the power supply of the amp, either electrically, or magnetically.

[Peckjed]

Originally Posted by kodabmx

No. That hum (if any) would be 120Hz. Are you sure it's not 120Hz?

60Hz usually is caused by ground loops/heater hum. If you short the inputs to ground, does the hum go away? If yes, it's a ground loop.
Does the hum go away as soon as you switch the amp off? If yes, this means it's coming from the power supply of the amp, either electrically, or magnetically.

There is a small amount of 120hz hum, but also lower frequency 60hz. (If my understanding is correct 120hz is higher pitched, almost a buzz and 60hz is lower pitched hum).

I’ll test if the hum goes away when shorting the input.
Yes, the hum goes away as soon as I power the amplifier off.

This is the power simply schematic: Legend power supply - Album on Imgur

Dumb question - can a choke be wired backwards?

[kodabmx]

Not usually, no... However I've read that the polarity can make a difference on certain chokes that were designed a certain way...