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In the Forum: Melquiades Amplifier
In the Thread: Single-stage Melquiades vs. DHT amps

Post Subject: I think we agree overallPosted by floobydust on: 1/20/2009

Okay... I also downloaded the original Milq SET amplifier PDF and have looked at it in detail as well as the 6-channel adaptation (DSET) and I understand where you're going with it... or so I think. In my particular situation, I've owned two pair of ESL-63s over the past 25 years. The lack of crossovers and coherency of a singlepoint source provides something in overall presentation that multi-driver systems have a difficult time with. Of course they are not perfect but it's also difficult to implement a multi-driver system that seamlessly integrates. It would appear that you and Dimi have spent considerable time to manage this as a system. At some point in time I will look for some very high sensitivity drivers and put some effort into integrating them... another fun project.

The exercise for the 6C33 was simply that... possibly a poor choice of words on my part, in either case we agree that it's a challenge to drive properly. Your choice of driver would seem logical and effective. While I would not accuse Russia of stealing the 6336 design, many tubes have used an existing type as a model... in most cases to improve upon it, such as the 6550 and MOV KT-88. In any case, the US manufacturers starting losing quality back in the 70's as solid-state gained acceptance and the actual (manufacturing) equipment was showing it's age and wear.

I agree that the 6E5P is an interesting tube for driver use. It is however a tetrode strapped as a triode, not that there is anything wrong with that. Once I get back stateside I'll look into acquiring a few to test with. As for other driver types to manage the voltage swing and current, the 6AH4 would be a likely candidate albeit lower gain. However, I don't think it's as simple as eliminating stages, but designing each stage with knowledge and consideration of both the preceeding and following stage. Following this methodology you can optimize the system as a whole and the number of cascaded stages from start to end will be what is required... ala Mozart, not too many notes but just the right amount ;-)

Integrating multiple amplifier sections and drivers is always a challenge. Doing it with different topologies and OPTs adds some additional complexity due to the difference in response characteristics. Crossover design for each of these adds more complexity and requires more effort to integrate, so I would certainly applaud your efforts here. You certainly have some interesting ideas to pursue on the crossover sections. Technically I don't think it should matter much if you use a DHT or IHT, it's still a single stage and should act similarly. I'm not sure if I buy into the belief that DHTs have a different sound that IHTs, but moreso that many of the designs may not have taken into consideration all of the design points they need to. DHTs add another element to the design, that of the filament and cathode being the same and the associated problems not only from designing with them but the physical internal construction differences and the simple fact that some work out better than others. Many of the DHT (brands) that have received glowing (pun intended) sonic compliments about just happen to be at the bottom of my list simply based on the internal construction and what I have measured and observed. If the tube is succeptible to mechanical vibration over a wide frequency range in the audible spectrum then it can't possibly provide a neutral amplification of the signal without adding a signature. Call it "tube warmth" or whatever... at the end of the day, it's still distortion.

I'll be sure to take a look into some of your recommended tube types... I still have to complete two designs and engineer builds for them... one being a 2A3 using the Hashimoto 20-watt OPTs and the other a WE300B design using the Hashimoto 30-watt OPTs. I have all of the iron and tubes. The WE300B design goal is for 10-watts. One odd thing to mention, for low-power SET amplifiers, I like using 1-watt as a reference point for measurements and specifications. As you move up, the additional power can be considered as headroom. I completely agree that it's important to measure and quote at full power bandwidth (anything less is cheating) but when you consider that most manufacturers quote signal-to-noise at their rated power, it becomes an inconsistent measurement and in many cases they don't specify what the S/N spec is relative to making it meaningless.

Regards, KM

PS - the RB300_CX... yes, a very cool toy... looked at that last year. Last I checked it was not available for purchase... too bad.

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