Clowkoy, my apologies in advance for this long winded reply. It's more, or less, a summary of everything I've said before and where, in my thinking, I'm at now on the subject. I'm hoping it will be my last post on the subject.
Quote:Clowkoy
There is actually a very simple solution to your problem: change the first capacitor to a polypropylene 3.9uf, like a Mundorf or Clarity cap.
Clowkoy, the problem to which you refer (rectifier tube/amp compatibility) IMO, is not just my problem, it's a problem for anyone who owns or contemplates purchasing a Decware SE34I.3 and contemplates tube rolling. At this point, at least for me, the jury is still out on whether it's the amp or the particular tube that's at the rooThere is no mention of any other type of 5U4 tube, i.e., 5U4GA, GBt of the problem in the first place. This is assuming there is a problem at all! Until I hear more from Steve, I shall reserve judgment. (skip to the last paragraph if you don't care to read any further)
As for replacing caps, that, IMO, could and probably would void the lifetime warranty, not to mention compromise Steve's intended design goal for this amp. While I may be somewhat ignorant about the internal workings of tube electronics, I get the feeling that changing a cap in a preamp is less problematic (read dangerous) than doing so in a power amp.
There is no mention of any other type of 5U4 tube, i.e., 5U4GA, GB
In the end, I have to believe that Steve knows how to build a proper amp for the tubes he selects and that he knows how to select caps with proper values so that those tubes operate correctly, within their intended specifications (NOS or current tubes), and without flashing issues (all this, notwithstanding what EML's Mr. van Walle implied in his email to me yesterday. See Reply #12 above).
Carefully reading the the Decware web site "Specifications" on rectification for the SE34I.3:
Quote:Rectification 5U4G tubes
There is no mention of any other type of 5U4 tube, i.e., 5U4GA, GB
and the pdf "Owner's Manual" for the SE34I.3 "Rachael":
Quote:There are also some compatible substitutes that you can try which include 5Y3GT and
5AR4. The 5AR4 is an indirectly heated rectifier with a soft start up so it may be a bit
more expensive than the 5Y3GT and 5U4. A popular rectifier tube that many people try
to substitute is the 274B. There are different manufactures and different types of 274B
rectifier tubes. Of the ones we’ve examined, they all required no more than a 10uf
capacitor in the first section of the power supply. Very few tubes amps today use that
small of a value. The SE34I.3 uses a 47uf capacitor in this location which can cause
the 274B to arc on start-up and thus reduce it’s life.
you now know the following:
1. the substitute rectifier tubes which could be a problem are some 274B's. A list of know problem 274B is not given;
2. the 5AR4 or 5Y3GT tubes are compatible substitutes for the 5U4G; and
3. any "5U4G" tube will work (NOS or current) since there is nothing in the manual or spec that states otherwise similar to the caution on the 274B. There is no mention of 5U4GB which is not electrically the same as a "5U4G", although, I think, it does appear to be safe to use from everything I've learned so far. We need Steve's confirmation on this.
What set me off on this journey was the OP's original question concerning "safe" rectifier substitutions for the SE34I.3 "Rachael". The OP wanted to know if it would be safe to substitute a 274B in place of a 5AR4/GZ34 AND his important notation of
flashing problems in WOO amps which used the Sophia 274B and
EML 5U4G.
To be clear, nowhere in this tread has it been stated that an EML 5U4G will flash and prematurely fail in the SE34I.3. The closest anyone in this thread has come to "suggesting" premature failure for the EML 5UG4, was "Marky" in replies #10 and 15 concerning what he read regarding the EML 5U4G tube on "other" forums, possibly with other non-Decware amps.
Nevertheless, the only reason I posted anything in this thread was because of the warning about tube-flashing of "EML 5U4G" tubes. I asked myself: why would the EML 5U4G flash in a Decware "Rachael" which is designed to accept a "5U4G"? By "a 5U4G" I am only referring to that specific tube, not to 5U4GA or 5U4GB.
When I looked at the EML 5U4G max capacitor spec on the EML web site, it was originally noted to be 33 uF and in less than 24 hours was quickly changed to 40 uF (as I noted in a post above). Both of those values were below Steve's selected cap value of 47 uF. Was this a potential flashing problem? Maybe. Lord Soth's "ballon" analogy in reply #8 on page 1, which explains how a tube can be stressed when used with a capacitor rated higher than the tube's max capacitor specification added to my concern. Adding more confusion, was the fact, pointed out by EML in their email to me, that the picture of the Decware SE34I.3 showed not a 5U4G, but rather a 5U4GB, an electrically different tube with a 40 uF cap rating. The 5U4GB is still 7 uF below the SE34I.3s 47 uF cap. Is this a problem or not?
Recognizing that tubes are tempermental beasts, and can fail at any time and for almost any reason, I am at the point of asking the following questions:
1. If the 5U4G and 5U4GB are electrically different tubes, are they safely interchangable (NOS or newer current types) in the "Rachael" in the same way 5AR4s or 5Y3GTs are safe substitutes? If not, why not?
2. If the "Rachael" is using a 5U4GB as the stock tube, rated at 40 uF max according to EML, why isn't this noted in the specifications to avoid confusion? Steve has confirmed in an email that the rectifier he is using (without exactly specifying the model tube) is working without issues, but he can't confirm that the EML 5U4G will work because he has never tested it in the Rachael. Excluding a bad tube, why wouldn't an EML 5U4G work properly? It seems to me the specifications should state which of the 5U4 family of tubes is safe to use.
So, in the end, I believe what is needed for the SE34I.3 is more and clearer information from Steve himself. Much akin to what he provides for the Mini Torii information page (pictures and descriptions of all the compatible tubes).