SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream.

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ SET Asylum ]

---

[ Alert Moderator ]

---

Very bad practice using 1.25K for single 300B...

Posted by Thomas Martens on March 2, 2007 at 15:33:14

In Reply to: You can use it in a mid-hi amplifier. posted by sser2 on March 2, 2007 at 11:44:51:

I'd avoid this combination as quite high distortion will be
the result --therefore defeating the reason for using high
linearity DHT tube such as the 300B in the first place.

Here is what can work alright: Parallel two 300B tubes and
set plate voltage and current/bias of EACH tube to the conventional
300B 2.5k operating parameters. you will obtain 12-14 watts of
fairly low distortion output this way.

Sorry, but there are simply no attractive alternatives for a single
300B and a 1.25k OPT. Frankly, the additional resistor idea is
a prodigious power-wasting move, and a very backwards approach
--guaranteed to sound crappy. You will be displeased.

Also: two parallel 2A3 will work optimally into such a load, and
give you a good solid 7-watts out.

If you are dead-set on using a single 300B, then I'd order-up the
excellent Hammond 1627 unit with a 2.5K primary. Yes, the Hammond
5K primary 1628 model should give lower distortion figures in the
midrange and low end, but at slightly reduced power than the 2.5K
unit, and some competent builders have complained about resonances
and high freq rolloff with this unit.

So the deal is:

(A) buying another pair of 300B and using orig 1.25k OPT for 12-14 watts out. (fairly low distortion)

(B) buying four new 2A3 tubes and using orig 1.25K OPT for 7 watts out
. (very low distortion)

(C) staying with the single 300B config but buying a new pair of
Hammond 1627 2.5K OPT's for about 7-8 watts out (fairly low distort-
ion, but and likely more sonically refined than option (A))

If the 300B tubes you would be needing for another matched
pair are in the approx $60 or so each range, then it might be a
tossup as far as price between option (A) and (B), with option
(C) costing somewhat more due to the shipping on new 11-lbs OPTs.

Personally, I'd probably pop for a new pair of 1627s, and go
for option C. You can always ebay your 1.25k units to defer
costs, or keep for another project.

Good Luck,

-T.M.

This post is made possible by the generous support of people like you and our sponsors:

Parts Connexion

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---