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RE: Filament bias and DHTs transformed my system.

Posted by tube wrangler on August 29, 2012 at 01:04:03:

Wow! You hit one out of the park this time, Andy!

I will take the time to comment-- maybe even more can be applied here:

(1) DHTs for everything. NO argument whatsoever. Only problem I have is how do you find DHTs with an amp-factor of 100, so you can Direct-Couple a two-stage?. I still think that your approach WILL result in very good fidelity. I'm really splitting hairs here-- well, almost. Two stages tied-together is a great thing! It acts just like ONE TRIODE if all is done right.

(2) Filament bias. Right-on. There is no better way to run a DHT. BUT--IF one buys the best caps, resistors and is VERY CAREFUL-- he can get cathode bias to work. It IS difficult. There are some advantages to it-- the bias provided by the cathode is signal-related, it's not fixed. I think you can get great results either way. The SOUND of each is different when each is optimized. Which do I prefer? EITHER!

(3) Transformer coupling all the way through. Well...... it CAN sound very excellent, BUT-- it does add some signal delay and some rolling-off of both highs and lows like all iron does. How much? How fat is your wallet? The better the iron, the better it gets. NO argument-- however, you have yet to hear really good D.C.-coupling. If you can get to RMAF 2012, do it. We'll have a ball with this discussion if you do. It will prove a great learning for us both.

(4) "hate" bypassed cathode resistors. I did too until I realized that I had to do it VERY right. The parts cost money, that's for sure. But don't hate it. Get the best resistors-- be sure to use two in parallel on the cathode. These must be within 1/100th of a percent of each other, so buy a few. If you don't get this close, you'll have two signals there. If you do, the two paths will make only one sound like a Tin Can (by comparison-- it's not THAT bad!). I suggest perfecting this before jumping off the cathode bias supply cliff.

(5) Truly, I think this forum has really excellent representation, and that includes the people who argue with me. There is real talent here. I would appreciate that argument not be politically motivated. The object is the best sound-- not the glitziest arguments, graphs, charts and proofs!

Thanks, Andy. I like your post-- a lot.

---Dennis---