From: info@turneraudio.com.au
On Wednesday, 2 January 2013 01:54:36 UTC+11, Sander deWaal wrote:
> patrick-turner said: >I wish all those who dabble
in tubes and various ways of coaxing them to give us pleasure a very fine
year. Same to you Pat & all other rodents. (yes, it's been more than 5 years!)
-- - Maggies are an
addiction for life. -
I have no sooner tested the use a single pentode to drive 2 complementary
source follower mosfets, 2SJ176 and 2SK56, in class A. I used a 2SK1924 for a
CCS feed of 25mA to EL34, with Ea = 220V. Trouble is that with Ra at such Ia
Ea = 46k, and although
gain is 150+, more than data µ suggest is ought to be, the input C of mosfets
of about 120pF begins shunting pentode output and causing 90d of phase lag, so
one ends up with needing lots of FB to flatten response. The situation is like
where you have
mosfet gates driven by high collector resistance, and I wanted ths
experimental amp to have BW at least = 300kHz to use it for a wide BW low Z
test signal source. During tests yesterday, the small old junk T used for B+
went up in smoke. Then I found the
EL34 was putting out 0.4Vrms of 50Hz and after hours of analysis I figured it
was induced stray magnetic field from plain old open frame PT for mosfet
stages nearby and affecting CCS mosfet - probably - but now the lot must be
unscrewed off breadboard
and re-made with potted PTs and allowing for more room for things.
Just having ONE SEP EL34 pentode to drive a pair of mosfets is not all bad,
because I can get THD > 1.2% at 10Vrms, all that is needed in this case with
+/- 16.5Vdc rails for mosfets. If the mosfet OP stage makes a typical 1% THD
at say 10Vrms output for
6.3 ohms, class A, then total dominant will be either about 2% or 0.4%
depending on what phase of 2H is, and that affects the amount of 2H
cancelling, and I've yet to actually drive the mosfets before finding out what
cancels. With say 26dB GNFB, if OLG
THD was 0.4%, many H, then CLG THD would be 0.02%, and excellent result
indeed!!!!. Maybe its too much to expect.
I have fall back plan to use EL86 in triode as driver with Ea = 220Vdc, Ia =
25mA, and Ra = 1.k4, able to push mosfets to over 300kHz! Gain would be 9, so
using an input tube of paralleled 12AU7 means EL86 only needs about 1.2Vrms
drive, and if GNFB is
used input can be 2Vrms with plenty of NFB. I fure a result may be better than
my experiment in 1999 when I made a nice OPT used with a quad of 2SK134in
class A and capable of 40W into 5 ohms at 0.2% THD.
Rather than allow my mind to rot to peices by sitting in a chair at a PC,
playing computer games, doing crossword puzzles, playing scrabble, or being at
the pub with one beer followed by another, I prefer having phone off hook,
being all day in shed on
days I don't ride 60km+ on bike and doing stuff all the time, despite aches
and pains. There's a Swedish made TV series playing here on Saturday nights
now show called "Real Humans". WOW, what an eye opener that is to how future
ppl will really get off
on personal robots, once they get them to look like us, and be able to drive,
shop, tie shoelaces, and cook dinner without smashing the car, looting the
shop, removing your foot, or burning the kitchen to a crisp!
A WHOLE new ball game awaits the grand kiddies but there could be troubles.....
Its only a matter of time before Squalid Stait is developed for robots to the
point where IQ is a routine 100, maybe costing $3,000, and then for
Einsteinobot, model with high IQ who can do all the kids home work for them
and offer all manner of economic
and medical advice and legal service might cost $10,000, easy-peasy for the
lazy middle class person. BJs could be optional, and by that I mean the
ability to knit a nice blue jumper for the winter.
Ah, the future. I won't be around for most of it. Oh, did you say you will be?
I barely tolerate those taking the Egyptian Solution, ie,'standing in de Nile'.
Now I must STFU and to the shed I muzzgo.
Patrick Turner.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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