Best looking tube?

[dirkwright]

What was the advantage of blue glass?

 

[tinitus]

mellow sound

 

[jerluwoo]

It was more of a trademark of Arcturus during the late 20s early 30s. They went to standard clear glass after then so they can be a bit rare. Saw some of the No.071 go for 50-150 dollars each on ebay.

 

[tinitus]

any tubes with matte sand(glass)plasted glass ?

 

[HoangVN]

it looks nice too! While it would be very energized shimmer.

 

[hpeter]

3D21 (WA) grounded screen looks interesting, maybe for driving directly electrostat speakers ... STAX...

 

[hpeter]

OT

re: hpeter

"intrigued by screen drive & G1 FB sound"

That is interesting, should make for some error correction at finite Fdbk, due to g1 having a higher exponent law for it's gm than g2. Has anyone tried this?

not sure if this is great idea, but...
realize a fat tetrode se, with direct coupled screen drive, and grid driven from opt secondary (potentiometer, variable fb to match "taste")

 

[smoking-amp]

"not sure if this is great idea, but..."

Yes, after thinking about such an approach, I realized that it would make the screen drive much more difficult, by requiring higher g2 drive to conteract the g1 NFDBK (causing screen current to become excessive).

A fix would be to only use just the error as feedback (unlike conventional feedback, this would pre-subtract the scaled output and input to get the small difference. Sometimes called Hawksford EC) That would likely solve the screen drive issue with only a tiny correction on g1.

But....., once one goes to the trouble of making a subtractor stage for the EC signal, it is already so effective in conventional NFDBK form as to not need the advantage of the finite Fdbk level with the g2 drive/g1 feedback idea.