GoodSoundClub - Romy the Cat's Audio Site

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

Post Subject: Why NOS tubes?Posted by floobydust on: 1/27/2009

While I would agree that modern construction should be much more robust than that of 5-6 decades ago, actual machining and manufacturing costs today are significantly higher than they were back then and there is much less of it going on. Look at your typical automobile... as little machining as possible... door locks, electronic.. instrument panel, all electronic, I'm convinced they would make the drive-train from silicon ships if they could. Case in point, 60 years ago, mechanical engineering and machine work were the pinnacle of the industrial age and the countries that did this. Also, the rigid controls of the EPA (in the USA) did not exist back then and the chemicals and processes where optimized for the best performance of the resultant product (the vacuum tube in this case). In today's world, the cost of doing this is almost cost-prohibitive. Ever wonder why the new Western Electric 300B tube costs so much? Try and get a triple chrome plating on a chassis and you'll see the impact on the bottom line costs... working with copper is ugly from an EPA perspective.

While the environmental controls may not be as rigid or present in some older eastern block countries (and Asia), as they get more integrated into the west this becomes a check point. No longer can a country engage in an old process with chemicals and dispose of the waste as they prefer to. I think this probably accounts for many reasons why certain aspects of tube engineering and manufacturing simply can not match what was done half a century ago. It's a simple matter of cost, and even the most devoted audiophile will have their limits.

As for your thoughts around doing a DHT implementation, you listed 4 tube types. I don't really know anything about the YO185 but would like to see some info if available. The others I do know... particularly the 45 and 2A3. In short, both of these are relatively easy to drive. The most obvious difference is the power output, which is a 3dB difference and the load impedance... 5K is optimum for the 45 and 3.5K for the 2A3. There are also many good NOS versions available even now, but costs are rising as availability decreases.

The 10Y was obsolete long ago and the preferred replacement was the 801. While they are similar they are not identical. There are two significant factors that differentiate these from the 45/2A3 variants: 1- They use a thoriated filament/cathode which requires 7.5V. 2- They require a fairly high load impedance (around 7K) and higher plate voltage (around 600V). The down side is also two-fold, higher impedance OPTs are more difficult to make and keep an extended high-frequency response. The filament/cathode design will require a DC supply to keep the hum out. You won't gain any additional output power over the 2A3... about 4-watts max. It will cost more to implement and it's doubtful if you'll get any (audible) improvement over a 2A3.

Finally, I'm not sure where your preceived need of four transformers comes from. I have 45 and 2A3 designs which are flat out to 45KHz at full power with low distortion and the only transformer in the signal path is the OPT. What is/was your thoughts on circuitry?

Regards, KM

Rerurn to Romy the Cat's Site