300Bs in Richmond

[Dave_in_VA]

Hi,
I just joined on the advice of a fellow on Audiokarma. We had been discussing switching from 5U4GBs to 5AR4s on my Manley 300B SEPP mono blocks.
I'm an old guy still collecting records after way over 50 years. I also like my reel to reel decks. I do listen to CDs when I'm reading so I don't have to get up and turn the record over.

So pretty much tubes, vinyl and tape. I know nothing about streaming.
More later.
Thanks,
Dave

[Grover Gardner]

Boy, have you come to the right place! That was my recommendation, Dave. Very nice to meet you, even though I'm "in exile" in Oregon (sob!). You'll find a lot of enthusiasm for your interests. I'm sure my fellow members will welcome you.

[FerdinandII]

Hi Dave,

My 300B SET is pretty sensitive to rectifier changes.
Stock from Factory: Mullard CV378, harsh and gritty
Optional: 5U4G, RCA ST-envelope sounds much more refined
My choice: 5R4, Lower operating point, smooth and detailed.

Welcome aboard.

BTW, Grover was the one who stuck some 5R4 "Potato Mashers" in my 300B amp at one of our meets and really set the rectifier experimentation phase in motion.

As always, YMMV

[Grover Gardner]

Hi Dave,

My 300B SET is pretty sensitive to rectifier changes.
Stock from Factory: Mullard CV378, harsh and gritty
Optional: 5U4G, RCA ST-envelope sounds much more refined
My choice: 5R4, Lower operating point, smooth and detailed.

Welcome aboard.

BTW, Grover was the one who stuck some 5R4 "Potato Mashers" in my 300B amp at one of our meets and really set the rectifier experimentation phase in motion.

As always, YMMV

OMG, I'd completely forgotten that.

[FerdinandII]

Hi Dave,

BTW, Grover was the one who stuck some 5R4 "Potato Mashers" in my 300B amp at one of our meets and really set the rectifier experimentation phase in motion.

OMG, I'd completely forgotten that.

Well, it was 15-20 years ago.....
The visual aesthetic was horrifying, but the sonic impact was convincing.

[Dave_in_VA]

Thanks.
I'm going to be limited to 5U4GB or 5AR4.
The Manleys originally shipped with 5U4GB (like mine) and switched to 5AR4 in 2012.
I was told the reason being was that in 2000 there was not a reliable supply of 5AR4s. This changed in 2012 and Manley started using the Ruby rectifier.
I like the idea of the slower warm up on my 300Bs (each amp uses two) but Grover made a good point about the 300B being designed when there were no 5AR4 rectifiers. But then again I have no idea how this amp is designed. It is unusual.
Also, not being a tech type, the whole subject is a little confusing to me.
Obviously, since the amps have worked fine with 5U4GBs for 20 years, I should probably leave well enough alone??
All of this speculation stems from concern about the expensive 300Bs in my amps.

[David McGown]

Dave,

Welcome to DCAudioDIY! I am sure that Grover probably advised you accordingly, but be careful of using rectifiers such as the 5R4 or WE274B since if your power supply is a CLC or CRC, the value of the first cap is critical, and should be no more than 10uF unless there is some additional series resistance between the rectifier output and the first filter cap. A 5U4 or 5AR4 is fine with a 40uF input cap, and would suggest keeping with them unless you find out more about the Manley power supply design. I actually like the tonal quality of the Chinese (Ruby) 5AR4, it has a nicer tonal balance than the Russian and Slovak (JJ) tubes, but does not convey as much "detail", in my opinion. But that is really dependent on the amp and system.

David

[Dave_in_VA]

Thanks.
I'm not considering anything other than trying some 5AR4s. I have a pair of vintage Mullards and ordered another pair of good testing vintage Mullards.
I just want what's best for my 300Bs and the amps came stock with 5U4GBs until 2012 and now comes stock with 5AR4s.
Trying to be careful.

[David McGown]

Dave,

Vintage Mullards will last a very long time so long as they are not abused (like a high input filter cap value). Probably should write Manley on this if you do not have a schematic. So if you have a pair and a spare (pair), you should be in good shape. I have been using a pair of the same Mullard (Phillips) 5AR4s for nigh on 20 years, moving from amp to amp.

David

[Grover Gardner]

Given that the amp has worked perfectly for so many years with 5U4s I can't see that the swap will cause any problems, and they do come with the 5AR4 now. But forgive us if we pick apart your amp for a minute.

This is a pretty cool design, switchable SE/PP with adjustable feedback settings. The power supply follows some different rules, however. You can see the schematics here:

https://www.radiomuseum.org/r/manleylabs_sepp_300b.html

5U4 full-wave bridge into 650uF!! I wouldn't even consider second-guessing Manley's designers, but it's interesting that they get away with that. The rectified DC is tapped off the rectifier filament supply center tap, with a hefty 100 ohm resistor before the caps, all of which, I assume, goes to protect the rectifiers from the effect of the large caps. Also, the B+ is not very high, and they don't appear to be running the 300Bs very hard, so the current demand on the rectifiers probably isn't excessive. It looks like a pretty conservative design.