Digital guy comes to tube land. I tried my first amp and like the
sound.

If anyone is interested: http://wosch.teratronik.com/amp/amp.html

Maybe you RATs can point me to all those big blunders I made...

I shamelessly posted a few questions onto that webpage and would
be happy for a few hints and tricks.

Keep glowing...
--
Olav Wölfelschneider

Hi RATs!

Welcome! You did the most important thing right: Got it working and listened

Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead

Hi Olav,

Maybe you RATs can point me to all those big
blunders I made...

Hmmm, let's see ...

- you feed the screen (g2) from an OPT tab more
positive (nearer to B+) than the plate. This
is very unusual. Is this a drawing error or
intentional? If intentional, what's the objective
behind that?

- the cathode resistors (R3, R7) of the ECC83 systems
seem to be extremely high (probably since you wanted
to reduce the gain of both stages). What plate current
do both ECC83 systems draw (each)?

At least for the gain/driver stages there probably are
better alternatives than using high gain (mu=100) sections
and then "destroying" the gain by such extreme plate/cathode
resistor ratios. At least on first sight I see no point
in using two such stages after another when a single
one with a less mu type triode section would do instead.

Or am I missing something?

Tom

--
If in doubt, mumble.

Tom Schlangen wrote:
Hi Olav,


Maybe you RATs can point me to all those big
blunders I made...


Hmmm, let's see ...

- you feed the screen (g2) from an OPT tab more
positive (nearer to B+) than the plate. This
is very unusual. Is this a drawing error or
intentional? If intentional, what's the objective
behind that?

This is usually called "Ultra-Linear" (UL), although originally UL
referred to a specific tap ratio (43% if I remember correctly). It
applies local feedback to the screen grid, and basically acts as a
topology halfway between normal pentode operation, and triode operation
(you could view triode operation as UL with 100% tap).

- the cathode resistors (R3, R7) of the ECC83 systems
seem to be extremely high (probably since you wanted
to reduce the gain of both stages). What plate current
do both ECC83 systems draw (each)?

At least for the gain/driver stages there probably are
better alternatives than using high gain (mu=100) sections
and then "destroying" the gain by such extreme plate/cathode
resistor ratios. At least on first sight I see no point
in using two such stages after another when a single
one with a less mu type triode section would do instead.

There may well be lower total distortion using this approach, since each
stage will have a lot of local feedback to linearize the response.

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects, Vacuum Tubes & other stuff: |
| http://www.dogstar.dantimax.dk |
+--------------------------------------------+

Hi Fred,


This is usually called "Ultra-Linear" (UL),
although originally UL referred to a specific
tap ratio (43% if I remember correctly).

Oh, Fred I, would simply call it pentode mode;
there's not a little bit UL in this circuit ;-)

Tom

--
The first rule of magick is simple: Don't waste your time
waving your hands and hoping, when a rock or club will do.

"Tom Schlangen" wrote in message
...

This is usually called "Ultra-Linear" (UL),
although originally UL referred to a specific
tap ratio (43% if I remember correctly).

Oh, Fred I, would simply call it pentode mode;
there's not a little bit UL in this circuit ;-)

Hi Tom

I've seen something like this done locally, selecting the taps on a similar
cheap PA output transformer to make a P/P ultralinear tube transformer (a
use for which it was _never_ intended).

If you look closely at the schematic, the screen is fed at some part of the
total primary impedance, but whether it's the usual ~43% is beyond my
knowledge, or maths ability (I suspect it's a bit higher).

It is, however, a basic UL circuit .....

Cheers

David

Hi Fred,

At least for the gain/driver stages there probably are
better alternatives than using high gain (mu=100) sections
and then "destroying" the gain by such extreme plate/cathode
resistor ratios. At least on first sight I see no point
in using two such stages after another when a single
one with a less mu type triode section would do instead.

There may well be lower total distortion using this approach,
since each stage will have a lot of local feedback to linearize
the response.

This may be, but:

A certain ammount of K2 distortion even may be desired
to cancel out the distortion of the power stage. And
probably the EL504 (a TV sweep circuit power tube)
generates quite some distortion in pentode (not UL)
mode.

Without having listened to such a design of course,
just from viewing the schematics, I still think that
the gain of roughly 4 x 4 = 16 of both stages in that
topology more easily and straight forward could be
obtained from other circuits with less parts (e.g
coupling caps) with more "fitting" tubes, than with
two capacitor coupled grounded cathode stages using
a high mu double triode like 12AX7/ECC83.

I mean, a gain of 16 really *screams* for other tubes
than a 12AX7/ECC83, and for a single stage with
a medium mu triode (even without a cathode bypass
cap).

At least, this is a rather unconventional way of
doing things, so maybe we both miss the point - lets
see what the author had in mind if he cares to elaborate
on this circuit and why he used this topology and
what its benefits are.

Tom

--
Life: All in all a bad game, but graphics are really good.

Olav Wölfelschneider wrote:


Digital guy comes to tube land. I tried my first amp and like the
sound.

If anyone is interested: http://wosch.teratronik.com/amp/amp.html

You may want to add in parallel a cap across R12, the 1K ultralinear
tap resistor. G2 needs a low impedance source to operate in ultralinear
mode properly. Not sure if 1K is low enough or not. G2 will draw some
plate current (which is varying according to what the control grid is doing)
and this varying current will (in a nonlinear fashion) vary the voltage
on g2
in addition to what the ultralinear tap and quiescent g2 current is doing.

Hi Olav,

regarding the question on your homepage about
NFB and oscillation:

Obviously you got positive feedback - so simply
ground the other end of the OPT secondary winding
and get the feedback voltage from the (now) not
grounded end.

Tom

--
The first rule of magick is simple: Don't waste your time
waving your hands and hoping, when a rock or club will do.