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In Reply to: Hitachi posted by Dave Pogue on March 13, 2007 at 05:48:27:
I'm using them for the front end of the Machine from now on, I have 140 Mullards and 200 Hitachi. IME, you have to get a few since, not being a dedicated audio device, they test a little scattery (not nearly as bad as the 5965, though). I built myself a pretty comprehensive test breadboard, I can test for rp, gm, and in-circuit gain. The Hitachis do test a little stronger and tighter than the Mullards; I have them in the amp breadboard now, and am trying different output transformers, coupling caps, O P points for the 6GKs (I'm using the IXYS chip CC in the tail, so I can dial the current in the front end with the twist of a screwdriver).Tell you what; I have a perfect quad of Mullards sitting right by the amp, I'll put them in there today and report back from this end.
Interesting,
Follow Ups:
What are the chances of a public domain 6GK5 Machine circuit any time soon?
Very good. I have the documentation, but it's not fit for public consumption, it has notes all over it. It's not that much different; The plate loads are 43.1K (91K || 82K) on both sides, and the tail is to a -66v supply (the seriesed secondaries of an Amveco 62025) through an IXYS 10M45 chip CCS set to between 4 and 4.5mA (I'm still experimenting with this); this because the tube takes enough current to get on the cam that I don't want to have the dissipation of a resistive tail heating up the inside of the chassis. I dig being able to reach into the breadboard and adjust the current in the front end with a screwdriver.By the way, I'm hearing very little difference between the Mullard and Hitachi tubes. The Mullards are perhaps just a bit clearer, the Hitachis a tiny bit juicier; both of them noticeably clearer and juicer than the 5965. I'm frustrated going back and listening to the 5965 amp when I have the breadboard up on the bench. The Mullards scare the sh!t out of me on fireup, though, two of them flare almost white hot.
I've had both MQ Brooklyn B18 pinstripe and Silk P-10-15 OTs in there, they also are surprisingly close; the B18 a little more visceral, the P-10 a bit more delicate. I think this is mostly the load difference, the B18 at 8K and the P-10 at 10K. I have Mundorf Silver coupling caps in there now, I have Rel RT (polystyrene/tin foil) and Solen SM (polypropylene/tin foil) to try; maybe today if I get a little hum fixed.
Aloha,
The Mullards tended to "flare" in my Premier 14, and I always assumed that was helping shorten their life. In any event, they never tested nearly as consistently or as strongly as the Hitachis in my (admittedly limited) Eico 667. Maybe I just got lucky with the Hitachis, but I've heard from others who had the same success with them.
No kidding. I just put them in there and started up; two of them scared me! I find it interesting that the general folklore seems to be, 'flare, hey, no problem!' It don't look cool to me, and I seem to recall some Sylvania yellow 12AX7s from my ancient history that did that and failed early.I'll burn them in awhile, and A-B with the Hitachis today. If the Japanese tubes are actually the daddy, I'll probably go get some more. One of my main ebay guys sells hundred bulk nests of them for $150; I already have two of them, so what could go wrong? I can tell you already that the Hitachis are a noticeable sonic improvement from the best of the 5965s, and the section matching problem that puts about a third of my 5965s in the circular file is a non-starter. Out of a hundred 6GKs, I get about 20 tight (1% or less) quads.
A Hui Hou,
They are very nice right out of the box. Like the Hitachis, very visceral and see-through. Terrific bassoon and guitar string tone. Great depth of image.
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