Rectifier tube 5AR4 vs. 5U4GB?

[WBS]

I found the attached rectifier comparison an interesting read:

http://www.kcanostubes.com/content/n...sp?ArticleID=3

Hope it lends insight!

[ChrisMmm]

Interesting, thanks.

Of course guitar amp criteria is a bit different than HiFi - they would probably prefer the lower end of the scale to maximise the distortion/feedback/sustain they desire.

This paints a clear picture if "sag" is the main criteria.

[scott17]

Are you saying that the CL150 is placed in series with the CT of the 5VAC and the first PS filter positive connection? I am using the 5U4GB and taking the HT from the 5VAC CT. I have a 30uF-630V 1st cap, 10H choke, and four 100uF-450V caps in a series-parallel configuration with balancing resistors to achieve a 100uF can with increased working voltage. I know that my filters can handle the initial high voltage surge, but I'm using a standby switch anyway by switching both sides of the HT AC to the rectifier, just for extra safety you know.

I guess my question is: Will the use of the CL150 further eliminate the need for the standby switch?

Originally Posted by Eli Duttman

A CL150 between the rectifier's filament and the PSU filter is (IMO) better. B+ rise is slowed down a tad and a bias supply (if present) still turns on immediately. If the 5 VAC winding has a CT, that's THE place to take the B+ from. B+ from pin 8, when types with cathode sleeves are employed. B+ from a CT, if available, when directly heated types are employed.

A word to the wise, a 5U4 can't tolerate as large a 1st filter cap. as a 5AR4 can. Be cautious.

[rknize]

The CL150 won't buy you much time, if that is what you are asking. They heat up in a few seconds...not really enough time for the tubes to heat up.

[Nikon1975]

I am always a bit surprise when I see people commenting on the sound of different rectifiers, as I think that what they are actually listening to is a different operating point of the output valve, unless the voltage is not adjusted with a variac. Am I correct ?

I use a 5R4GYA or 5AR4 with the tubelabSE and a 5AR4 for the SimpleSE, as they are sharing the same PSU. there is around 35 V of difference and the 5AR4 comes up much slower.

D.

[kevinkr]

Originally Posted by Nikon1975

I am always a bit surprise when I see people commenting on the sound of different rectifiers, as I think that what they are actually listening to is a different operating point of the output valve, unless the voltage is not adjusted with a variac. Am I correct ?

I use a 5R4GYA or 5AR4 with the tubelabSE and a 5AR4 for the SimpleSE, as they are sharing the same PSU. there is around 35 V of difference and the 5AR4 comes up much slower.

D.

It may be a combination of different operating point due to higher/lower B+, but it may also be the result of a significant change in the internal resistance of the rectifier. IMHO the audibility of different tube rectifiers in an amplifier is a good indication that the supply is actually a significant part of the audio path which is not necessarily the sign of a good design, but not always entirely avoidable either.

[Nikon1975]

Let's see if I understood something:
I took the specs of the 5AR4 and of the 5U4GB (just to make an exercise)
I see that the 5AR4 has a plate impedence of 160-200 ohm per plate. The 5U4GB has an impedence between 21 and 67 ohm. So let's assume 180 ohm for the 5AR4 and 50 ohm for the 5U4GB. I guess I have to multiply by two, so I get 360 ohm for the 5AR4 and 100 for the 5U4GB.

So, if I am thinking right, I would expect the reduced impedence of the 5U4GB to allow for a faster recovery of the reservoir capacitor after it is partially discharged for a transient.

I have to say that the 5U4GB has a though requirement on the minimum resistance of the transformer, so this eats up most of the benefit.

If I just replace the rectifier, and keep all the rest the same, I am changing the output voltage and the impedence of my power supply, and this should be what gives the difference in the sound.

Is it correct ?

I am asking as I want to make some test on the power supply, that in my case can power three different amps I have, starting for the simplest configuration to end up with a regulated PSU, and I would like to have control and understanding on the parameters involved.

Thanks,

Davide

[JoshK]

The diodes are in parrallel, not in series, so that would be 90 and 25 ohms in your example.

[kevinkr]

Also I am not quite sure where you got those numbers from, generally the 5AR4 IME appears to have significantly lower internal losses and hence less voltage drop than a 5U4 at a given current up to its rated current.

[Nikon1975]

What you say makes sense. I took the data of the 5U4G from the Sylvania data sheet. The file is too big to be attached. Not sure about the 5AR4.
Actually I am not sure that I am picking the right number. I am looking at "Effective plate supply impedance "

Best Regards,

Davide