A brief rectifier update:
Carlsbad, as you know, there are 2 main types of GZ34 rectifiers; the ones made by Mullard in England, and those made by Philips in the Netherland (that go by various names; Amperex, Philips Mini-watt, Dario etc). Both are excellent but they are totally different in sound. The Mullards are much warmer whereas the Dutch are far more neutral. You might wish to try both in your DAC to see what works best for your system.
If you wish to explore 4V rectifers, there is a very good alternative to spending big bucks on the Valvo G2504.
Many astute tube collectors know that the Valvo AZ12 is electrically identical to the RGN2504 and G2504 but with a different pin base (Y8A for AZ12 vs 4-pin B4 for the RGN2504 or Valvo G2504) and a slightly different capacitor specification for the transformer it couples to (which is a non-issue for the Horizon). My previous experience with the 4 volt rectifiers were equivocal, but the issues raised by other experienced users were whether the adapters I used were a limiting factor in their performance in my system.
https://www.whatsbestforum.com/thre...be-rolling-paradise.34477/page-44#post-881362 post #874
Therefore, I thought I might revisit this issue recently. Since I thought the overall balance of the RGN2004 was somewhat light in the upper bass and therefore not a good fit for classical music, I limited my re-evaluation to the RGN2504 variant which I thought was a better fit for orchestral music in my system. However since the RGN2504 or Valvo G2504 are essentially unobtainable (>$700 if you can find one), I thought that I would try the far more affordable and electrically identical variant which is the Valvo AZ12 with the Y8A straight-pin base. As you all know, there are some excellent 3rd party adapters available now for the G2504/RGN2504. However, before pulling the trigger, I wanted to revisit the AZ12 to see if my views changed on its sonics. One advantage of the AZ12 plus a ebay adapter is that the cost is <$100; whereas an authentic G2504/RGN2504 plus T/P adapters will run >1K, if you can find one).
I ordered a few stock AZ12 to 5U4G ebay adapters thinking that if I liked what I heard, I would modify the stock ebay adapter resistors and thus wind up with a nice performing tube at an bargain price.
Well, here’s a surprise I didn’t expect. It seems that the guy who makes the Chinese ebay adapter for an AZ12 never tried one in his adapter! If he did, he would realize that the AZ12 does not seat properly because the resistors he uses in his adapter are too thick to allow the tube to seat properly. I then did some adapter surgery to see what the heck was going on.
View attachment 119989
Once I got a good look at the innards, I was able to spread the 2 resistors apart a bit and flattened them which now allowed the AZ12 tube to seat securely in the adapter. Once I figured out how to flatten the resistors, I was able to flatten then on the stock adapter without butchering the base (as shown in the photo). It turns out the resistors used in the Chinese adapters are actually pretty good metal film resistors. I was expecting some cheap carbon resistors so I bought some resistors that are non-inductive Vishay/Caddocks to replace them. However, after 40 years of building crossovers, I’m not sure there’s going to a significant performance gain based purely on the resistor swap for the sole purposes of regulating voltage from 5 to 4 volts since metal film resistors are quite adequate for that purpose. (Their values are also correct and need no change from stock). However, in fanaticville, we are fond of saying “everything matters”, so I’ll look forward to getting around to installing the Vishay non-inductive resistors and see if they make a difference.
Once I managed to get the AZ12 seated properly in the stock Chinese adapter, I was able to listen to the AZ12 and found that it is indeed a very good regulator. The dynamics and bass response is outstanding. I plan to do some more extended listening once I get around to replacing the stock resistors with my Vishay/Caddocks. I admit I still have some of the original concerns I had that I had with the RGN2504 which was a lack of top end air and detail, but I’ll look forward to seeing if a resistor swap changes that original impression. In the meantime, the Cossor 53KU still reigns supreme for me as it hits all the right notes in combo with my other tubes. However, that tube is also a pricey one ($600+), which makes the AZ12 plus a modified stock Chinese adapter (with flattened resistors) a terrific audio bargain at under 100 bucks!. That alone, is a really big plus for tube rollers. Try it and let us know what you think.
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