Quote: The EML 5U4G was on the short list, a very short list. However, the 40uF limitation bothered me so I called EML. The person that I spoke with made it very clear that the tube was designed to work with a cap value of 40uF and could not comment on what sort of life it would have if it was used in a circuit that used a 47uF cap. I appreciated the candor.
Joman.....when I read the notes section of the EML 5u4G tube, it indicated that if if the cap exceeded the recommendation of the 40 uF, it would cause not only shorten the life of the tube, but also would place stress on the capacitor and shorten it’s life).
Here is what was listed in the note section...
Quote: Notes
Note 2) To prevent large charge current peaks, the first capacitor (C1) should NOT be larger than 40uF. If the input capacitor is too large, this will result in heavy AC charge current through this capacitor. This is not good for the rectifier tube, and also not for the capacitor lifetime. The AC capacitor current peaks may cause hum radiation into the preamplifier. With the given C-L-C values in table, the rectifier circuit will work best. For filtering, with oversized components, you will have best results by increasing the choke. Do not oversize capacitor C1, this may increase hum. You can choose the choke large as you want. This will have better results with high voltage rectification.
A shortened tube life since it’s an external component doesn’t bother me as much ( unless it’s something like 1/2 or more) BUT..... weakening the 1st capacitor definitely bothered me since it’s an internal component.
I would really love to find out from Steve his take on using a rectifier that exceeds the 1st capacitor rating of 7uF (40 uF vs 47 uF) and its overall potential damage to not only the 1st capacitor, but the rest of the internal components of the Zen Amp.
I am going to ask my sister who is an electrical engineer, but she designs power systems for buildings and does not build audio amplifiers. So I’m sure her take on the question is going to be very different than Steve’s
Dom