• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Developing a 2A3 SET

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#146
Another Alternative. First Pass.
One volt at the input drives the 2A3 to clipping. 👍
 

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#147
jhstewart9 said:
Another Alternative. First Pass.
One volt at the input drives the 2A3 to clipping. 👍
Click to expand...
I am struggling to understand it. The first stage seems to operate at a very non-linear low voltage low current region for this type of tube. Why not running it at its recommended high current? Plate resistance would be low enough to make the cathode follower unnecessary. Then, on top of it, this isn't exactly one of the most linear triodes.

If additional CF stage is considered, a pentode driver can be very substantially improved. Like E80F/C.F. driver with less than 0.2 Vrms in and less than 1% driver THD at 2A3 clipping.
 
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#148
As the short note sez, it is a first pass. The first stage plate current is 1.77 mA. In this sim I’m simply looking at cct voltage & current levels.

The finale version was to be a small pentode triode. There are a few suitable, for example the 6AN8 or 6U8. I rejected several others since the Pd of their triodes was not high enough to support the high current of the CF.
Many underestimate the performance of these meant for TV & FM tubes. While doing the performance tests on my take of Crowhurst’s Twin Coupled Amp I put together two adapters for the amp front end, a two stage differential amplifier. The 6SL7 & 6SN7 were replaced with 6BQ7’s. The measured performance is much better than most would have thought. Primarily because they heard what others were saying but never tried to check the results themselves. The distortion measurements were taken by a PicoTech virtual instrument & an HP 334A THD meter.

There are a few designers with vacuum tube experience here on DIY. The rest simply throw darts & hope for a good outcome.
 

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#149
jhstewart9 said:
There are a few designers with vacuum tube experience here on DIY. The rest simply throw darts & hope for a good outcome.
Click to expand...
That seems harsh, misplaced and makes too many assumptions.
It's not hard to design and build a tube amplifier.
This is supposed to be fun, remember?.
--
jdrouin: how are you going with your 2A3 adventures?
 
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#150
It's easy to build something to 1930's standards of performance, although even that, at its best, was a pretty demanding standard. And it's easy to build something to 1950's standards of safety, but just don't. But are either of these the goal of modern DIY builders? I would argue that, except for Sakuma "I adjust by smell" specialists, most folk want to build something that is the best that they can make it. "Best" is a big word and will forever be discussed, of course.

Folk like jhs have probably seen too much foolishness, too many commonly repeated errors, too much voodoo and reptile extracts, too much worship of pre-War circuitry, and would like to start newer devotees off on a better footing than is often printed elsewhere. DIYaudio is helpful in this because it encourages immediate corrections to errors in thinking and modeling, saving folk valuable time. These corrections are not criticisms or personal insults - instead, they are the highest form of compliments. "You are worth my time to give this correction." That's what DIYaudio is about.

All good fortune,
Chris
 
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#152
Chris Hornbeck said:
"..most folk want to build something that is the best that they can make it. "Best" is a big word and will forever be discussed, of course."
Click to expand...
Just a friendly reminder that the original poster outlined five 2A3 established designs that he would build and evaluate - thats all.
Kind regards
---
jdrouin: how are you going with your 2A3 adventures?
 
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#153
As I wrote it is better to build something that is certified by test lab.
And, as usual, the quality is strictly related to the quality of OT trafo, first.

cit.
When you can measure what you are speaking about,

and express it in numbers, you know something about it;

but when you cannot measure it, when you cannot express it in numbers,

your knowledge of it is of a meager and unsatisfactory kind:

it may be the beginning of knowledge, but you have scarcely,

in your thoughts, advanced to the stage of science.



William Thomson, Lord Kelvin of Largs (1824-1907)
 
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#156
I cant help but notice that "gerritube" has retracted his 'support' for "waltube" - what a coordinated effort; who knew.
Anyway, you hyenas are a perfect example of why otherwise good people stay away from here.
---
jdrouin: how are you going with your 2A3 adventures?
 
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#159
Chris Hornbeck said:
I would argue that, except for Sakuma "I adjust by smell" specialists, most folk want to build something that is the best that they can make it. "Best" is a big word and will forever be discussed, of course.
Click to expand...
Chris - I really like what you say. There are straightforward, unquestionanle paths to goodness, like choosing most linear tubes, finding operating points with least distortion, understanding both advantages and limitations of different topologies. A rational designer follows these paths and hopes for good outcome. Hopes, but is not assured of. There are many things that nobody understands well, which can make a difference between "good" and "best".
 
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