Another custom tube amp

[erik2A3]

Thanks for posting those PDFs Maynard - looks like a neat amp, configuring for triode use would be interesting to try, and could be done with a switch for convenience/comparison.

It's always been interesting to me to consider what design goals and parameters surrounded designs like this, and how much of a chosen circuit was dependent on an interest in keeping costs of parts and construction as low as possible. I was reading an article wiritten in the 1930s about the benefits and virtues of direct-coupling the other day. Of course it was referring to radio rather than hi fi audio circuitry, but radio is what cleared the land for the development of what we enjoy now. At that time in history, cost of building would certainly have been a significant concern for some, and while I generally prefer to spend less if and where possible, I also really, really like the sound of a well-designed circuit that does not need capacitors (cheap ones or insanely expensive ones) for coupling one stage to the next. In other words, simplicity can indeed be less expensive, but that fact does NOT necessarily mean one is making a sonic compromise.

I know someone who is an internationally well-known designer of single-ended amplifiers and headphone amps. Several years ago he sold my wife (who, believe it or not was the one who negotiated the purchase!! such an absolute sweetheart!) the schematic, chassis (the very last one of this particular model) and power and output transformers for a direct-coupled 2A3 circuit that became highly successful and very well-reviewed. He told me that the basis of the circuit was derived from an amplifier his dad built for him, and was constructed from a few parts his father happened to have in a parts bin. From input to to output, not a single interstage coupling capacitor to speak of, yet its sound is marvelous -- immediate, with very clean and clear mid and high frequency reproduction. The only change I made to the circuit was to use AC to heat the 2a3 instead of regulated and highly filtered DC as specified, using a separate filament transformer for each channel.

Looking forward to hearing more about your grid-leak bias amplifier!

Edited March 8, 2014 by erik2A3

[erik2A3]

And Maynard, just for the record, I raised the example of direct coupling as it relates to historical circuit design. It's not presented as being superior to an AC coupled amp in any way -- just so you know. They are both unique, different, and elegantly simple in their own way and for their own reasons.

[bracurrie]

Peanut gallery question: I have a love affair with tight and fast bass. As a non-technician I have come to understand the damping factor has a lot to do with tight and fast bass. And with my tube amps I still find my SS amp tighter and faster for bass but tube amps better for midrange and highs. Hence my preference for active crossover bi-amped systems.

Question:

Can you get a better damping factor in tube amps? If not why?

[markgodski]

http://www.tube-amps.net/EA.htm

, Concerning how Hashimoto transformers effect the sound of various tube amps . some info . on tube amp projects by Mr. Tadaatsu Atashari

Has allot of different info concerning tube amps , tied into Sansui tube amps and more .

Edited March 8, 2014 by markgodski

[tube fanatic]

Peanut gallery question: I have a love affair with tight and fast bass. As a non-technician I have come to understand the damping factor has a lot to do with tight and fast bass. And with my tube amps I still find my SS amp tighter and faster for bass but tube amps better for midrange and highs. Hence my preference for active crossover bi-amped systems.

Question:

Can you get a better damping factor in tube amps? If not why?

The issue of how important damping factor is has gone on for a long time. To answer your question, yes it is possible to get better damping factors for tube amps; but, as to whether it matters...........

This short article explains some of the relevant points quite well imo:

http://www.butleraudio.com/damping1.php

Maynard

[erik2A3]

bracurrie: Not a peanut gallery question in the least! We are all on the same playing field in this common hobby/obsession! I agree with you. In fact I bi-amp my system for the same reason, with an SS amp on La Scala bass bins, and a variety of tube amps on my Lowther drivers mounted to a large open baffle. I do plan to complete the conversion of two tube stereo OTL amplifiers I have for the bass bins, however. They'll be used as monoblocks. I have a couple of push-pull tube amps, though, including a fairly recently completely disassembled and rebuilt Leak ST20, that are outstandingly good, including bass response.