Quote:Posted by: Tony Posted on: Yesterday at 21:08:10
Here is what Sophia Electric says on their page for this product:
....To fully utilize its benefits, it may require the first stage capacitor (capacitor input) to be less than 10MFD; otherwise, it would shorten the 274B life span...
Can someone unpack that statement and relate it to Deware amps in general or more specifically to a SE84UFO25?
A bottom line is all the UFO amps have a 47 uF input capacitor.
That part is unambiguous, what you do about it gets more fuzzy. If you want to play by the "rules" the two common rectifiers that are spec'd for a 47 uF input capacitor are the 5U4G and 5AR4 aka GZ34. If you buy those (assuming they meet the spec for a new tube) you are playing by the rules and done all you can. Maybe...
But, at least IMO, the real situation is more complicated. The rectifier can't know and doesn't care specifically what the the value of the input capacitor is. What it cares about is the so called "inrush current" that it sees as the input cap gets charged up when you turn on your amp. The bigger the input cap the bigger the inrush current. And while it is possible to calculate the current based on some assumptions I think it is fair to say the capacitor value is more of a guideline than a rule. And hence the complication/ambiguity/confusion.
I just checked the datasheet for one of the few current production tubes I own, the Genalex Gold Lion GZ34 and it doesn't specify the input cap, it specifies the "current surge at turn on" which is 3.7 amps which is a really big number. Many NOS rectifiers (from back when more people cared about datasheets and read them carefully) specify both a max input cap and a max current value and in many cases they are wildly inconsistent. The example I point to is what many consider the ultimate 5U4 type rectifier, the Western Electric 422A. The datasheet specs are a max input cap of 8 uF and a max input current of 4 amps (!!!!). So if you have a UFO amp and are considering a 422A rectifier (which would cost as much as your amp) you have to decide if the 8 uF first cap spec would scare you away or the 4 amp current spec would give you confidence that the rectifier is more than up to the task. I would go by the latter.
My bottom line is many (most) common NOS rectifiers are spec'd for relatively small input caps, typically much smaller than 47 uF, but for big inrush currents, typically at least 1 amp. Likely much bigger than the UFO amp will ever see (for higher powered amps I suspect the situation is similar, but I can't say for sure). Also, tubes made during the "golden age of tube tech" often greatly exceed their datasheet requirements, which are a minimum requirements tube must meet to be considered "good". Current production is much more of a question, again JMO YMMV.
So, lots of people use lots of different rectifiers in their UFO amps a usually they last a long time. But there are no guarantees (well some tubes are sold with guarantees, but what I'm talking about is their actual service life), for good or bad. Any tube, and esp. any rectifier is subject to failure at any time. And any tube, even the cheapest current production Chinese, can give you years of trouble free service. That's what you sign up for when you buy a tube amp.