I am hoping that someone in this group can help me out on this one. I have
been working on an amplifier design for some time now. It is a Hybrid
amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but hear
me out. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the
preamplifier and predriver stages and a class-A output stage using BJT's.
The output BJT's that I am using are 2SA1303 and 2SC3284, but will probably
change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage is
directly coupled to the Vacuum tube predriver stage and the preamplifier to
predriver stages are capacitively coupled. The design is not my own, but I
got the schematics from a good friend who works as an Electrical Engineer
for a very high end home audio company. I have heard this design actually
play. It really did sound quite good. I digress. Here is my problem.

If I attempt to play any audio prior to the vacuum tubes being fully warmed
up, it has a tendency to rail negative at the outputs. Transistors are
rather expensive when you go thru them like popcorn. Actually, I have been
able to add protection circuitry to keep the output devices from blowing up.
But, I believe that I could probably take out a tweeter or two if I'm not
real careful. I have Apogee Speakers with their wonderful ribbons, and I
really don't want to damage something that can not easily be replaced.

What I am thinking of doing is to add a couple of relays at the speaker
outputs, and then driving them on only when the vacuum tubes have properly
warmed up. What I don't know is just exactly when to drive them on. I
could simply use an RC timer circuit that waits x seconds and then drives on
the relays. But, if ambient temperature is much colder than normal, then
this is not a really great solution. Instead, I was thinking of placing
thermistor(s) in close contact with the vacuum tubes and then analog *and*
these thermistors via a set of comparator circuits to eventually drive the
relays on. That way, the relays would only activate when all the vacuum
tubes are up to temperature.

Now, what I don't know is at what temperature is a vacuum tube considered
"warmed up". I am looking for a general answer for a minimum temperature
that would be considered safe. I know that different vacuum tubes probably
will operate at vastly different temperatures.

BTW I love valve amplifiers and I extoll their virtues to all who will
listen. Sadly, few do. My world is that of car audio and if it doesn't
have the ability to drive the impedance of a nail with all the power in
Thor's mighty hammer, then it doesn't sell. You are thinking then, why the
hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low
impedance that any low cost Valve amplifier can't drive.

Thoughts, commentary and ideas anyone?


Regards,


John Andreen

John Andreen wrote:


What I am thinking of doing is to add a couple of relays at the speaker
outputs, and then driving them on only when the vacuum tubes have properly
warmed up. What I don't know is just exactly when to drive them on. I
could simply use an RC timer circuit that waits x seconds and then drives on
the relays. But, if ambient temperature is much colder than normal, then
this is not a really great solution. Instead, I was thinking of placing
thermistor(s) in close contact with the vacuum tubes and then analog *and*
these thermistors via a set of comparator circuits to eventually drive the
relays on. That way, the relays would only activate when all the vacuum
tubes are up to temperature.

Rig a circuit that measures the current from the cathodes of the tubes.
Almost by definition,
a tube is warmed up when it is drawing at least 90% of the current it
will normally draw. If
measuring cathode current is awkward, measure the current going to the
plates and screens.
Measuring the current is the best thing to do, as this tells you exactly
what you need to know.
Measuring the temperature of the glass bulb of a tube doesn't really
tell you when a tube
is ready to go to work. And if the power should go off for a short
while, the glass
won't cool off for a long while.


Now, what I don't know is at what temperature is a vacuum tube considered
"warmed up". I am looking for a general answer for a minimum temperature
that would be considered safe. I know that different vacuum tubes probably
will operate at vastly different temperatures.

BTW I love valve amplifiers and I extoll their virtues to all who will
listen. Sadly, few do. My world is that of car audio and if it doesn't
have the ability to drive the impedance of a nail with all the power in
Thor's mighty hammer, then it doesn't sell. You are thinking then, why the
hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low
impedance that any low cost Valve amplifier can't drive.


How about using output transformers? You can use a transformer normally
rated for
say 2000 ohms impedance to 4 ohms impedance for 2 ohm loads. However
the input
impedance will change from 2K to 1K, but the power handling will be 3dB
less. More bass
though. So use
bigger transformers. With audio transformers, when operating at
impedances below those
specified, power capability is lower and the frequency spectrum is
shifted downward,
conversely, at higher impedances power capability and frequency spectrum
will be shifted upward. Then you can go all tube without the BJTs. And the
transformers give excellent DC isolation to the speakers.

Be sure to enclose the tubes so moving objects don't damage them or get
damaged by the tubes. And firmly bolt the amp down (but check before
drilling
holes in the trunk that you don't puncture into the gas tank!).

just set timer for 15 sec.
dc sensing protection circ on output will do the rest of job.

--
.................................................. ........................
Choky
Prodanovic Aleksandar
YU

"don't use force, "don't use force,
use a larger hammer" use a larger tube
- Choky and IST"
- ZM
.................................................. ...........................
...
"John Andreen" wrote in message
news:_Mmkb.70789$vj2.17282@fed1read06...
I am hoping that someone in this group can help me out on this one. I
have
been working on an amplifier design for some time now. It is a Hybrid
amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but
hear
me out. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the
preamplifier and predriver stages and a class-A output stage using BJT's.
The output BJT's that I am using are 2SA1303 and 2SC3284, but will
probably
change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage
is
directly coupled to the Vacuum tube predriver stage and the preamplifier
to
predriver stages are capacitively coupled. The design is not my own, but
I
got the schematics from a good friend who works as an Electrical Engineer
for a very high end home audio company. I have heard this design actually
play. It really did sound quite good. I digress. Here is my problem.

If I attempt to play any audio prior to the vacuum tubes being fully
warmed
up, it has a tendency to rail negative at the outputs. Transistors are
rather expensive when you go thru them like popcorn. Actually, I have
been
able to add protection circuitry to keep the output devices from blowing
up.
But, I believe that I could probably take out a tweeter or two if I'm not
real careful. I have Apogee Speakers with their wonderful ribbons, and I
really don't want to damage something that can not easily be replaced.

What I am thinking of doing is to add a couple of relays at the speaker
outputs, and then driving them on only when the vacuum tubes have properly
warmed up. What I don't know is just exactly when to drive them on. I
could simply use an RC timer circuit that waits x seconds and then drives
on
the relays. But, if ambient temperature is much colder than normal, then
this is not a really great solution. Instead, I was thinking of placing
thermistor(s) in close contact with the vacuum tubes and then analog *and*
these thermistors via a set of comparator circuits to eventually drive the
relays on. That way, the relays would only activate when all the vacuum
tubes are up to temperature.

Now, what I don't know is at what temperature is a vacuum tube considered
"warmed up". I am looking for a general answer for a minimum temperature
that would be considered safe. I know that different vacuum tubes
probably
will operate at vastly different temperatures.

BTW I love valve amplifiers and I extoll their virtues to all who will
listen. Sadly, few do. My world is that of car audio and if it doesn't
have the ability to drive the impedance of a nail with all the power in
Thor's mighty hammer, then it doesn't sell. You are thinking then, why
the
hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low
impedance that any low cost Valve amplifier can't drive.

Thoughts, commentary and ideas anyone?


Regards,


John Andreen

Simple answer: the God of Triodes is paying you back for putting silicon
in the signal path. :-}

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"John Andreen" wrote in message
news:_Mmkb.70789$vj2.17282@fed1read06...
I am hoping that someone in this group can help me out on this one. I
have
been working on an amplifier design for some time now. It is a Hybrid
amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but
hear
me out. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the
preamplifier and predriver stages and a class-A output stage using BJT's.
The output BJT's that I am using are 2SA1303 and 2SC3284, but will
probably
change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage
is
directly coupled to the Vacuum tube predriver stage and the preamplifier
to
predriver stages are capacitively coupled. The design is not my own, but
I
got the schematics from a good friend who works as an Electrical Engineer
for a very high end home audio company. I have heard this design actually
play. It really did sound quite good. I digress. Here is my problem.

If I attempt to play any audio prior to the vacuum tubes being fully
warmed
up, it has a tendency to rail negative at the outputs. Transistors are
rather expensive when you go thru them like popcorn. Actually, I have
been
able to add protection circuitry to keep the output devices from blowing
up.
But, I believe that I could probably take out a tweeter or two if I'm not
real careful. I have Apogee Speakers with their wonderful ribbons, and I
really don't want to damage something that can not easily be replaced.

What I am thinking of doing is to add a couple of relays at the speaker
outputs, and then driving them on only when the vacuum tubes have properly
warmed up. What I don't know is just exactly when to drive them on. I
could simply use an RC timer circuit that waits x seconds and then drives
on
the relays. But, if ambient temperature is much colder than normal, then
this is not a really great solution. Instead, I was thinking of placing
thermistor(s) in close contact with the vacuum tubes and then analog *and*
these thermistors via a set of comparator circuits to eventually drive the
relays on. That way, the relays would only activate when all the vacuum
tubes are up to temperature.

Now, what I don't know is at what temperature is a vacuum tube considered
"warmed up". I am looking for a general answer for a minimum temperature
that would be considered safe. I know that different vacuum tubes
probably
will operate at vastly different temperatures.

BTW I love valve amplifiers and I extoll their virtues to all who will
listen. Sadly, few do. My world is that of car audio and if it doesn't
have the ability to drive the impedance of a nail with all the power in
Thor's mighty hammer, then it doesn't sell. You are thinking then, why
the
hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low
impedance that any low cost Valve amplifier can't drive.

Thoughts, commentary and ideas anyone?


Regards,


John Andreen

Thank you for the very informative response. I think that I will indeed
measure the current flowing into the Vacuum tubes. Not real hard to do
really. I had considered that back in 1998, but gave it up due to
complexity. Your input made me take another look. Already found a cool
hall effect sensor ( considered using MAXIM's IC before) that will really do
a nice job.

Kudo's, Kudo's, Kudo's. I am indeed greatful for this input as I was certain
that bottle temperature would be a terrible lag lead location. Thought that
by measuring the pin temperature would be somewhat better. Your idea is
much better. Thanks.

I do know that most Valve amplifiers use the Audio transformers. Did a
short study a long time ago using my companys 2 KRELL KA300's ( I think),
and a high end tube amplifier that we had for evaluation at Apogee in our
sound lab. I do not recall the amplifier brand. I don't even know if it
was branded come to think of it. Came from Europe though, probably Germany.
Anyways I ran the Valve amplifier with a Pass Labs preamplifier and a KRELL
CD player. Played this through a pair of Totem acoustics speakers. OMG,
the music was wonderful! The listening material was comprised of Mahalia
Jackson, Claire Marlo ( Let It Go), Yello (Baby) and Thursday Diva (Follow
Me). Next I ran a set of Apogee Diva's on the Valve amplifier setup. Could
only play at relatively low volume and it didn't sound good. Tried again
with a much less demanding pair of Apogee Ribbon/Hybrid's. I think they
were Perseus's. Once again the music sounded stunning!

I then did the same listening test with the KRELL's as the amplifier stage.
Outstanding musicallity with the Diva's and the other two speaker pairs. I
came to the conclusion that the Diva's really need a low impedance source to
drive them properly. They also liked POWER. The Diva's when properly
operated were simply the best speakers that I have ever heard. Maybe I'm
biased.

My mind isn't completely made up about audio transformers. But the
**really** good ones are ballistically expensive and take up an awful lot of
room. Too bad nobody has been able to make a better, more efficient
transformer. I guess you could throw make it the size of a cigarette pack
too. That is why I keep looking back at hybrid designs. Hell, I even know
some of the Engineers that are still working on ways to make a silicon based
amp sound just like a tube. 10+ years and still not even close.

John

"Robert Casey" wrote in message
...
John Andreen wrote:


What I am thinking of doing is to add a couple of relays at the speaker
outputs, and then driving them on only when the vacuum tubes have
properly
warmed up. What I don't know is just exactly when to drive them on. I
could simply use an RC timer circuit that waits x seconds and then drives
on
the relays. But, if ambient temperature is much colder than normal, then
this is not a really great solution. Instead, I was thinking of placing
thermistor(s) in close contact with the vacuum tubes and then analog
*and*
these thermistors via a set of comparator circuits to eventually drive
the
relays on. That way, the relays would only activate when all the vacuum
tubes are up to temperature.

Rig a circuit that measures the current from the cathodes of the tubes.
Almost by definition,
a tube is warmed up when it is drawing at least 90% of the current it
will normally draw. If
measuring cathode current is awkward, measure the current going to the
plates and screens.
Measuring the current is the best thing to do, as this tells you exactly
what you need to know.
Measuring the temperature of the glass bulb of a tube doesn't really
tell you when a tube
is ready to go to work. And if the power should go off for a short
while, the glass
won't cool off for a long while.


Now, what I don't know is at what temperature is a vacuum tube considered
"warmed up". I am looking for a general answer for a minimum temperature
that would be considered safe. I know that different vacuum tubes
probably
will operate at vastly different temperatures.

BTW I love valve amplifiers and I extoll their virtues to all who will
listen. Sadly, few do. My world is that of car audio and if it doesn't
have the ability to drive the impedance of a nail with all the power in
Thor's mighty hammer, then it doesn't sell. You are thinking then, why
the
hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather
low
impedance that any low cost Valve amplifier can't drive.


How about using output transformers? You can use a transformer normally
rated for
say 2000 ohms impedance to 4 ohms impedance for 2 ohm loads. However
the input
impedance will change from 2K to 1K, but the power handling will be 3dB
less. More bass
though. So use
bigger transformers. With audio transformers, when operating at
impedances below those
specified, power capability is lower and the frequency spectrum is
shifted downward,
conversely, at higher impedances power capability and frequency spectrum
will be shifted upward. Then you can go all tube without the BJTs. And
the
transformers give excellent DC isolation to the speakers.

Be sure to enclose the tubes so moving objects don't damage them or get
damaged by the tubes. And firmly bolt the amp down (but check before
drilling
holes in the trunk that you don't puncture into the gas tank!).

Thank you very much for your input. I do have a DC sense circuit for the
outputs ( shamelessly stolen from somewhere). I also have a small servo
that can correct for up to about +/- .5 DC.

John


"Choky" wrote in message ...
just set timer for 15 sec.
dc sensing protection circ on output will do the rest of job.

--
.................................................. .......................
Choky
Prodanovic Aleksandar
YU

"don't use force, "don't use force,
use a larger hammer" use a larger tube
- Choky and IST"
- ZM

.................................................. ...........................
..
"John Andreen" wrote in message
news:_Mmkb.70789$vj2.17282@fed1read06...
I am hoping that someone in this group can help me out on this one. I
have
been working on an amplifier design for some time now. It is a Hybrid
amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but
hear
me out. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the
preamplifier and predriver stages and a class-A output stage using
BJT's.
The output BJT's that I am using are 2SA1303 and 2SC3284, but will
probably
change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage
is
directly coupled to the Vacuum tube predriver stage and the preamplifier
to
predriver stages are capacitively coupled. The design is not my own,
but
I
got the schematics from a good friend who works as an Electrical
Engineer
for a very high end home audio company. I have heard this design
actually
play. It really did sound quite good. I digress. Here is my problem.

If I attempt to play any audio prior to the vacuum tubes being fully
warmed
up, it has a tendency to rail negative at the outputs. Transistors are
rather expensive when you go thru them like popcorn. Actually, I have
been
able to add protection circuitry to keep the output devices from blowing
up.
But, I believe that I could probably take out a tweeter or two if I'm
not
real careful. I have Apogee Speakers with their wonderful ribbons, and
I
really don't want to damage something that can not easily be replaced.

What I am thinking of doing is to add a couple of relays at the speaker
outputs, and then driving them on only when the vacuum tubes have
properly
warmed up. What I don't know is just exactly when to drive them on. I
could simply use an RC timer circuit that waits x seconds and then
drives
on
the relays. But, if ambient temperature is much colder than normal,
then
this is not a really great solution. Instead, I was thinking of placing
thermistor(s) in close contact with the vacuum tubes and then analog
*and*
these thermistors via a set of comparator circuits to eventually drive
the
relays on. That way, the relays would only activate when all the vacuum
tubes are up to temperature.

Now, what I don't know is at what temperature is a vacuum tube
considered
"warmed up". I am looking for a general answer for a minimum
temperature
that would be considered safe. I know that different vacuum tubes
probably
will operate at vastly different temperatures.

BTW I love valve amplifiers and I extoll their virtues to all who will
listen. Sadly, few do. My world is that of car audio and if it doesn't
have the ability to drive the impedance of a nail with all the power in
Thor's mighty hammer, then it doesn't sell. You are thinking then, why
the
hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather
low
impedance that any low cost Valve amplifier can't drive.

Thoughts, commentary and ideas anyone?


Regards,


John Andreen

I know, I know, but I come from the car audio amplifier world where silicon
is king. Its kind of really all I know.

I will say, that I have been studying Valve amplifiers for a few years.
Still not able to actually make good comparative
reference between BJT's and Vacuum tubes. I matriculated collegiately
during the mid 70's and silicon was all that was taught. I am learning
though. I even purchased TubeCAD to help me out. It didn't help any when I
brought up the subject to my peers in card audio. They slammed Vacuum tube
amplifiers, saying horrible things, the nicest being that they called Vacuum
tubes "Watt sucking glow FET's". Being willing to compromise, I am shunned
by both sides.

Most of my silicon based car audio amplifier designs are as simple as
possible. If it doesn't need to be in the signal path, then I don't put it
there. No crossovers, no bass boost, no treble boost. Hell, not even gain
pots. That stuff belongs elsewhere, like in a preamplifier. My design
never fly with my boss's as they say they won't sell. They are mostly
right, as it is all a matter of perception. More is always better, right?

I will say this though, you guys are most certainly the nicer of the two
camps.

Thanks for the prudent observation!

John

"Tim Williams" wrote in message
...
Simple answer: the God of Triodes is paying you back for putting silicon
in the signal path. :-}

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"John Andreen" wrote in message
news:_Mmkb.70789$vj2.17282@fed1read06...
I am hoping that someone in this group can help me out on this one. I
have
been working on an amplifier design for some time now. It is a Hybrid
amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but
hear
me out. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the
preamplifier and predriver stages and a class-A output stage using
BJT's.
The output BJT's that I am using are 2SA1303 and 2SC3284, but will
probably
change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage
is
directly coupled to the Vacuum tube predriver stage and the preamplifier
to
predriver stages are capacitively coupled. The design is not my own,
but
I
got the schematics from a good friend who works as an Electrical
Engineer
for a very high end home audio company. I have heard this design
actually
play. It really did sound quite good. I digress. Here is my problem.

If I attempt to play any audio prior to the vacuum tubes being fully
warmed
up, it has a tendency to rail negative at the outputs. Transistors are
rather expensive when you go thru them like popcorn. Actually, I have
been
able to add protection circuitry to keep the output devices from blowing
up.
But, I believe that I could probably take out a tweeter or two if I'm
not
real careful. I have Apogee Speakers with their wonderful ribbons, and
I
really don't want to damage something that can not easily be replaced.

What I am thinking of doing is to add a couple of relays at the speaker
outputs, and then driving them on only when the vacuum tubes have
properly
warmed up. What I don't know is just exactly when to drive them on. I
could simply use an RC timer circuit that waits x seconds and then
drives
on
the relays. But, if ambient temperature is much colder than normal,
then
this is not a really great solution. Instead, I was thinking of placing
thermistor(s) in close contact with the vacuum tubes and then analog
*and*
these thermistors via a set of comparator circuits to eventually drive
the
relays on. That way, the relays would only activate when all the vacuum
tubes are up to temperature.

Now, what I don't know is at what temperature is a vacuum tube
considered
"warmed up". I am looking for a general answer for a minimum
temperature
that would be considered safe. I know that different vacuum tubes
probably
will operate at vastly different temperatures.

BTW I love valve amplifiers and I extoll their virtues to all who will
listen. Sadly, few do. My world is that of car audio and if it doesn't
have the ability to drive the impedance of a nail with all the power in
Thor's mighty hammer, then it doesn't sell. You are thinking then, why
the
hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather
low
impedance that any low cost Valve amplifier can't drive.

Thoughts, commentary and ideas anyone?


Regards,


John Andreen

Somewhere in dark past ( ) I build DC300B (I think from AA) hybrid amp
with one my friend;
line up is something like triode strapped EF86 on input,then 2 x ECC82 in
White Follower ,then 2 pairs of Mosfets on output.
trust me-even if White Follower wasn't direct coupled with
mosfets,thumpboingoink cycle was evident.
installing 15 sec delay for powering xformer for output stage cured
everything.
if you have mutual xformer for tube and SS supply,you can implement sort of
mute circ in tube output part.
I mention DC sense circ only as speaker protection precaution,which is must
have for every amp DC coupled to speakers.

"John Andreen" wrote in message
news:3SDkb.71248$vj2.17708@fed1read06...
Thank you very much for your input. I do have a DC sense circuit for the
outputs ( shamelessly stolen from somewhere). I also have a small servo
that can correct for up to about +/- .5 DC.

John


"Choky" wrote in message
...
just set timer for 15 sec.
dc sensing protection circ on output will do the rest of job.

--

.................................................. ........................
Choky
Prodanovic Aleksandar
YU

"don't use force, "don't use force,
use a larger hammer" use a larger tube
- Choky and IST"
- ZM


.................................................. ...........................
..
"John Andreen" wrote in message
news:_Mmkb.70789$vj2.17282@fed1read06...
I am hoping that someone in this group can help me out on this one. I
have
been working on an amplifier design for some time now. It is a Hybrid
amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......,
but
hear
me out. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the
preamplifier and predriver stages and a class-A output stage using
BJT's.
The output BJT's that I am using are 2SA1303 and 2SC3284, but will
probably
change to On Semiconductor MJW21193 and MJW21194's. The BJT output
stage
is
directly coupled to the Vacuum tube predriver stage and the
preamplifier
to
predriver stages are capacitively coupled. The design is not my own,
but
I
got the schematics from a good friend who works as an Electrical
Engineer
for a very high end home audio company. I have heard this design
actually
play. It really did sound quite good. I digress. Here is my
problem.

If I attempt to play any audio prior to the vacuum tubes being fully
warmed
up, it has a tendency to rail negative at the outputs. Transistors
are
rather expensive when you go thru them like popcorn. Actually, I have
been
able to add protection circuitry to keep the output devices from
blowing
up.
But, I believe that I could probably take out a tweeter or two if I'm
not
real careful. I have Apogee Speakers with their wonderful ribbons,
and
I
really don't want to damage something that can not easily be replaced.

What I am thinking of doing is to add a couple of relays at the
speaker
outputs, and then driving them on only when the vacuum tubes have
properly
warmed up. What I don't know is just exactly when to drive them on.
I
could simply use an RC timer circuit that waits x seconds and then
drives
on
the relays. But, if ambient temperature is much colder than normal,
then
this is not a really great solution. Instead, I was thinking of
placing
thermistor(s) in close contact with the vacuum tubes and then analog
*and*
these thermistors via a set of comparator circuits to eventually drive
the
relays on. That way, the relays would only activate when all the
vacuum
tubes are up to temperature.

Now, what I don't know is at what temperature is a vacuum tube
considered
"warmed up". I am looking for a general answer for a minimum
temperature
that would be considered safe. I know that different vacuum tubes
probably
will operate at vastly different temperatures.

BTW I love valve amplifiers and I extoll their virtues to all who will
listen. Sadly, few do. My world is that of car audio and if it
doesn't
have the ability to drive the impedance of a nail with all the power
in
Thor's mighty hammer, then it doesn't sell. You are thinking then,
why
the
hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather
low
impedance that any low cost Valve amplifier can't drive.

Thoughts, commentary and ideas anyone?


Regards,


John Andreen

John Andreen wrote:

I am hoping that someone in this group can help me out on this one. I have
been working on an amplifier design for some time now. It is a Hybrid
amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but hear
me out.

75 watts of class A means that you would have to have approximately
160 watts of idle dissipation in the transistor outputs.
Even for the most rugged devices 80 watts of heat from each is a heck of a lot
to expect continuously.
How many devices have you got? If it were my amp, I'd have at least 6 devices,
perhaps 3 npn, and 3 pnp, in a complementary pair set up.
This way the dissipation can be held to less than 30 watts per device,
with far greater reliablity.
is it common emitter, or common collector?

Remember, for SS, for each extra 10C temp rise, there is a 10% fall in
reliability.
a 100C temp rise = 100% fall in reliability, ie, it WILL fail.


I am using all vacuum tubes, mostly Svetlana 6LCGC's in the
preamplifier and predriver stages and a class-A output stage using BJT's.
The output BJT's that I am using are 2SA1303 and 2SC3284, but will probably
change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage is
directly coupled to the Vacuum tube predriver stage and the preamplifier to
predriver stages are capacitively coupled.

We really need to see a schematic!

The design is not my own, but I
got the schematics from a good friend who works as an Electrical Engineer
for a very high end home audio company. I have heard this design actually
play. It really did sound quite good. I digress. Here is my problem.

If I attempt to play any audio prior to the vacuum tubes being fully warmed
up, it has a tendency to rail negative at the outputs. Transistors are
rather expensive when you go thru them like popcorn. Actually, I have been
able to add protection circuitry to keep the output devices from blowing up.
But, I believe that I could probably take out a tweeter or two if I'm not
real careful. I have Apogee Speakers with their wonderful ribbons, and I
really don't want to damage something that can not easily be replaced.

You say there are 6L6 tubes used to drive the bjts, and these are directly
coupled.

Most full SS amps have ALL direct coupling, with an enormous amount
of total feedback, perhaps 30 dB in the output stage, in the form of
common collector array, ie, emitter follower complementary pair,
and then they have perhaps 50 dB of global FB to a differential pair of bjt at
the input.
This automatically reduces the DC offset at the output to less than a few mV,
regardless of the operating temp of ANY devices used which are included in the
amp loop.

RC coupled preamp stages should not affect the DC offset, unles they are
included in the fedback loop, which then couldn't be all direct coupled.
ALL direct coupled SS amps have the greatest FB at DC,
so thats where the greatest control of output voltage occurs.



What I am thinking of doing is to add a couple of relays at the speaker
outputs, and then driving them on only when the vacuum tubes have properly
warmed up.

I think your problem has little to do with tube temperature.
But we cannot be certain, because you have not posted a schematic which we can
properly analyse.


What I don't know is just exactly when to drive them on. I
could simply use an RC timer circuit that waits x seconds and then drives on
the relays.

Timed relays are used on much SS gear, but also the relay
turn on circuit is controlled by fault detection circuits, and it isn't until
the DC offset is low at the output that the relay will trip on, to connect
speakers,
when its safe to do so.

But, if ambient temperature is much colder than normal, then
this is not a really great solution. Instead, I was thinking of placing
thermistor(s) in close contact with the vacuum tubes and then analog *and*
these thermistors via a set of comparator circuits to eventually drive the
relays on. That way, the relays would only activate when all the vacuum
tubes are up to temperature.

This sounds like a nightmare to R&D!



Now, what I don't know is at what temperature is a vacuum tube considered
"warmed up". I am looking for a general answer for a minimum temperature
that would be considered safe. I know that different vacuum tubes probably
will operate at vastly different temperatures.

It depends how you are running the tube.
We need a schematic!



BTW I love valve amplifiers and I extoll their virtues to all who will
listen. Sadly, few do. My world is that of car audio and if it doesn't
have the ability to drive the impedance of a nail with all the power in
Thor's mighty hammer, then it doesn't sell. You are thinking then, why the
hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low
impedance that any low cost Valve amplifier can't drive.

For car audio, and for those who like brain mashing levels of sound,
fitting a pair of amps like those shown at
http://www.turneraudio.com.au/htmlwe...00monobloc.htm
would be difficult to implement, but two of the amps shown
will provide 600 watts of power.
The problem is, where do you place 100 kGs of hot hardware,
and you would need a 1 kW inverter.
Maybe someone with a huge mobile trailer home might use them....

There is no problem driving low loads, and the above amps are
able to be matched to 2 ohms, without losses.

Most tube amps with OPTs don't have sufficient multiple secondary
sectionjs to allow them to be coupled to less than 4 ohms.
But I assure you that with sufficient secondary sections, and by using ALL of
them
AND with equal current density in all of them, then a match to 1 ohm
is quite possible.


Thoughts, commentary and ideas anyone?

BTW, I have built a pair of class A mosfet output stages coupled to the speakers
with an OPT,
and driven by 3 x small signal transitors.
See http://www.turneraudio.com.au/webpic...no400w288h.jpg
See http://www.turneraudio.com.au/htmlwe...5050mosfet.htm
The driver transitors are RC coupled to the output stage, which has 4 x 2SK134,
arranged like a
quad of tubes, and RC coupled to the transformer.
Fixed bias is used for the class A mosfets, since they have a negative
temp coefficient, which means they conduct less current as they get hotter,
so fixed bias is safe.
There is no need for output relays, since there is NO direct couping,
and the output fets cannot let DC pass the the speakers from the rails in a
fault condition.
The amp's full power response is 10 Hz to 65 kHz, sufficient for all of what I
listen to.

I am planning to upgrade these class A mosfet amps by use of 2SK369
j-fet devices in the input/driver stage, and hopefully that will silence the
critics
who are prejudiced about transistors.
Some are prejudiced against mosfets,
and even j-fets, and I hope they recover from their ailment soon.

Long Live Output Transformers!!!
( Those who say it can't be done, just cannot do it;
so, may they learn.)

Finally, I use EL84 strapped as triodes for driver tubes, since one is equal to
5 halves of a 6SN7.
Now in a class A tube power amp, the EL84 in an output stage
is run at 12 watts dissipation, with say B+ = 300v, and Ia = 40 mA.
But in driver situation, I typically run the EL84 at Ea = 240v, and Ia = 15 mA,
and the temperature is a lot less.
Both either application, the working temp is correct.
Minor differences in ambient temp will affect the tube temp,
but not enough to dramatically upset the working of the circuit
where it works.
BJTs on the other hand are HORRIBLY temperature sensitive,
and troubles with class A amps "running away thermally"
is not uncommon, becaue the hotter they get, the more current they conduct,
ie, they have a horrible positive thermal coeficient.

I have never had any reason to ever use a BJT in an outout stage yet
on any amp.
Also, BJTs need to have a high current applied to their bases to drive them,
which may be why you have to use a 6L6 to do that.
Darlingtom pair connection will reduce this drive current.
But I just use mosfets, because their gate drive is high impedance, like a tube.

The down side is that mosfets have high input capacitance, but using
appropriate low impedance drive circuitry to achieve a
high time constant for the RC involved solves that problem.


Patrick Turner.



Regards,

John Andreen

Most tube amps with OPTs don't have sufficient multiple secondary
sectionjs to allow them to be coupled to less than 4 ohms.
But I assure you that with sufficient secondary sections, and by using ALL of
them
AND with equal current density in all of them, then a match to 1 ohm
is quite possible.


If I understand the high power car audio area correctly, they use many
speakers
wired in parallel. To get a very low impedance so you can get a lot of
power from
12V DC. If you rewire the speakers to present a higher load impedance, you
should be able to drive them with a convential tube amp circuit with
convential
output transformers. A series/parallel arrangement of the speakers. (I
can understand
that this may not be an option in the market, though. Not "swap it
out/in and play")
As far as the amp's power supply, run all the heaters off of the 12VDC
(the value
6.3V for heaters came from tube manufacturers wanting to make tubes for car
radios). The 6.3V output tube heaers can be wired in series for use on 12V.
But you need to have a DC-DC converter from 12V to the B+ you need at the
current you need. A switchmode supply operating around 100KHz
(frequency to avoid
noise in the audio, also no beat frequencies from audio and 100KHz
invading the
audio spectrum).

Patrick,

Thanks again for all the wonderful insight.

I would love to provide a schematic, but I do not know the legalities
involved. It is in fact intellectual property of a
rather large audio company. They have deep pockets and mean lawyers. Trust
me on this, I know whom they have
litigated and sent into the depths of oblivion. I was only given a copy of
the schematic out of friendship and on the
condition that I won't reveal it. It could also compromise my friend and
his position. As a side note, this companies Non-Disclosure agreement is 28
pages of legalistic mumbo jumbo and folderol. I can however, publish a
schematic of my modified design when I am completed or near completion. I
must be able to show that this is my own design, complete with a minimum of
7 unique differences. This is really why I am asking some of the questions
that I ask. Slowly but surely identifying the *major* design flaws and then
creating my own circuits to hopefully correct them. I may know much about
silicon audio, but I am for sure a pleeb at vacuum tubes.

When I get home, I will check the schematic and count the output devices.
Just from memory, I am certain that there are at least 6 sets of
complementary pairs. Car audio is really a harsh environment to design
for( this is not the case for my design, as I want to drive my Apogee's at
home). Most output devices are operated at a maximum heatsink temperature
of about 90 degrees C. So taking into account device derating, it is rather
common to use an excess of output devices. And, in a car, it could be in
Gnome, Alaska one day and in Death Valley the next.

Currently, I am still working on the PS sections. This includes the tube
heaters, the +/- 300 volt rails for the tubes, +/- 18 volt rails for the
rails for the output BJT's, and the +/- 15 volt rails for the support
circuitry. Haven't made it to the audio sections yet. Hell, I am still
having a tough time understanding that there is only 1 kind of tube and not
P and N tubes like transistors.

This might seem like another odd question, but has anyone ever made an audio
amplifier using anything like the really big transmitting tubes. I used to
work on multi-kW RF generators in the '70s. They used to scare me to death
when I worked on them due to having to use a grounding bar to discharge the
large glass capacitors. Kept thinking that I would one day forget to do
this and vaporize myself.

I little more info is probably needed to clarify some of my posts. The
original design was ment to be used in a car audio
environment. It was never produced. The gentleman that designed the
amplifier now works for a well known home audio company. The company that
holds the intellectual property on the original design is a large card audio
company. Although my considerate friend no longer works for the car audio
company, were he to be sued for IP theft, it would not look good to his
current employer. I want to use this amplifier design as a base for a home
style amplifier to power my Apogee Ribbon speakers. Check this site for
Apogee info: http://www.apogeespeakers.totalserve.co.uk Although it is a
hybrid, I do like the sound of the original amplifier. This is pretty much
a labor of love, or I probably would have given up and simply made a Leach
amplifier with more outputs. Check this site for Leach amplifier info:
http://users.ece.gatech.edu/~mleach/lowtim
It too is a nice sounding amplifier. Please don't hate me for this, but if
you look into the Apogee Speakers, you will see just how difficult they are
to drive even with really big KRELL amplifiers. This is why I am willing
to compromise and do a design that uses both worlds. I have done many
spectral analysis tests on both valve and SS amplifiers. I can see the
differences. I can even hear the difference. Valve amplifier sound makes
me feel more relaxed and comfortable. With many SS amplifiers, I feel as if
I should be clenching my fists in anger. Perhaps a hybrid amplifier will
make me feel more
comfortable while clenching my fists.

John Andreen

BTW: I live in AZ, and many of my "tubehead" friends use supplemental air
conditioning units in their audio rooms. Is this normal?

Patrick Turner" wrote in message
...


John Andreen wrote:

I am hoping that someone in this group can help me out on this one. I
have
been working on an amplifier design for some time now. It is a Hybrid
amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but
hear
me out.

75 watts of class A means that you would have to have approximately
160 watts of idle dissipation in the transistor outputs.
Even for the most rugged devices 80 watts of heat from each is a heck of a
lot
to expect continuously.
How many devices have you got? If it were my amp, I'd have at least 6
devices,
perhaps 3 npn, and 3 pnp, in a complementary pair set up.
This way the dissipation can be held to less than 30 watts per device,
with far greater reliablity.
is it common emitter, or common collector?

Remember, for SS, for each extra 10C temp rise, there is a 10% fall in
reliability.
a 100C temp rise = 100% fall in reliability, ie, it WILL fail.


I am using all vacuum tubes, mostly Svetlana 6LCGC's in the
preamplifier and predriver stages and a class-A output stage using
BJT's.
The output BJT's that I am using are 2SA1303 and 2SC3284, but will
probably
change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage
is
directly coupled to the Vacuum tube predriver stage and the preamplifier
to
predriver stages are capacitively coupled.

We really need to see a schematic!

The design is not my own, but I
got the schematics from a good friend who works as an Electrical
Engineer
for a very high end home audio company. I have heard this design
actually
play. It really did sound quite good. I digress. Here is my problem.

If I attempt to play any audio prior to the vacuum tubes being fully
warmed
up, it has a tendency to rail negative at the outputs. Transistors are
rather expensive when you go thru them like popcorn. Actually, I have
been
able to add protection circuitry to keep the output devices from blowing
up.
But, I believe that I could probably take out a tweeter or two if I'm
not
real careful. I have Apogee Speakers with their wonderful ribbons, and
I
really don't want to damage something that can not easily be replaced.

You say there are 6L6 tubes used to drive the bjts, and these are directly
coupled.

Most full SS amps have ALL direct coupling, with an enormous amount
of total feedback, perhaps 30 dB in the output stage, in the form of
common collector array, ie, emitter follower complementary pair,
and then they have perhaps 50 dB of global FB to a differential pair of
bjt at
the input.
This automatically reduces the DC offset at the output to less than a few
mV,
regardless of the operating temp of ANY devices used which are included in
the
amp loop.

RC coupled preamp stages should not affect the DC offset, unles they are
included in the fedback loop, which then couldn't be all direct coupled.
ALL direct coupled SS amps have the greatest FB at DC,
so thats where the greatest control of output voltage occurs.



What I am thinking of doing is to add a couple of relays at the speaker
outputs, and then driving them on only when the vacuum tubes have
properly
warmed up.

I think your problem has little to do with tube temperature.
But we cannot be certain, because you have not posted a schematic which we
can
properly analyse.


What I don't know is just exactly when to drive them on. I
could simply use an RC timer circuit that waits x seconds and then
drives on
the relays.

Timed relays are used on much SS gear, but also the relay
turn on circuit is controlled by fault detection circuits, and it isn't
until
the DC offset is low at the output that the relay will trip on, to connect
speakers,
when its safe to do so.

But, if ambient temperature is much colder than normal, then
this is not a really great solution. Instead, I was thinking of placing
thermistor(s) in close contact with the vacuum tubes and then analog
*and*
these thermistors via a set of comparator circuits to eventually drive
the
relays on. That way, the relays would only activate when all the vacuum
tubes are up to temperature.

This sounds like a nightmare to R&D!



Now, what I don't know is at what temperature is a vacuum tube
considered
"warmed up". I am looking for a general answer for a minimum
temperature
that would be considered safe. I know that different vacuum tubes
probably
will operate at vastly different temperatures.

It depends how you are running the tube.
We need a schematic!



BTW I love valve amplifiers and I extoll their virtues to all who will
listen. Sadly, few do. My world is that of car audio and if it doesn't
have the ability to drive the impedance of a nail with all the power in
Thor's mighty hammer, then it doesn't sell. You are thinking then, why
the
hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather
low
impedance that any low cost Valve amplifier can't drive.

For car audio, and for those who like brain mashing levels of sound,
fitting a pair of amps like those shown at
http://www.turneraudio.com.au/htmlwe...00monobloc.htm
would be difficult to implement, but two of the amps shown
will provide 600 watts of power.
The problem is, where do you place 100 kGs of hot hardware,
and you would need a 1 kW inverter.
Maybe someone with a huge mobile trailer home might use them....

There is no problem driving low loads, and the above amps are
able to be matched to 2 ohms, without losses.

Most tube amps with OPTs don't have sufficient multiple secondary
sectionjs to allow them to be coupled to less than 4 ohms.
But I assure you that with sufficient secondary sections, and by using ALL
of
them
AND with equal current density in all of them, then a match to 1 ohm
is quite possible.


Thoughts, commentary and ideas anyone?

BTW, I have built a pair of class A mosfet output stages coupled to the
speakers
with an OPT,
and driven by 3 x small signal transitors.
See http://www.turneraudio.com.au/webpic...no400w288h.jpg
See http://www.turneraudio.com.au/htmlwe...5050mosfet.htm
The driver transitors are RC coupled to the output stage, which has 4 x
2SK134,
arranged like a
quad of tubes, and RC coupled to the transformer.
Fixed bias is used for the class A mosfets, since they have a negative
temp coefficient, which means they conduct less current as they get
hotter,
so fixed bias is safe.
There is no need for output relays, since there is NO direct couping,
and the output fets cannot let DC pass the the speakers from the rails in
a
fault condition.
The amp's full power response is 10 Hz to 65 kHz, sufficient for all of
what I
listen to.

I am planning to upgrade these class A mosfet amps by use of 2SK369
j-fet devices in the input/driver stage, and hopefully that will silence
the
critics
who are prejudiced about transistors.
Some are prejudiced against mosfets,
and even j-fets, and I hope they recover from their ailment soon.

Long Live Output Transformers!!!
( Those who say it can't be done, just cannot do it;
so, may they learn.)

Finally, I use EL84 strapped as triodes for driver tubes, since one is
equal to
5 halves of a 6SN7.
Now in a class A tube power amp, the EL84 in an output stage
is run at 12 watts dissipation, with say B+ = 300v, and Ia = 40 mA.
But in driver situation, I typically run the EL84 at Ea = 240v, and Ia =
15 mA,
and the temperature is a lot less.
Both either application, the working temp is correct.
Minor differences in ambient temp will affect the tube temp,
but not enough to dramatically upset the working of the circuit
where it works.
BJTs on the other hand are HORRIBLY temperature sensitive,
and troubles with class A amps "running away thermally"
is not uncommon, becaue the hotter they get, the more current they
conduct,
ie, they have a horrible positive thermal coeficient.

I have never had any reason to ever use a BJT in an outout stage yet
on any amp.
Also, BJTs need to have a high current applied to their bases to drive
them,
which may be why you have to use a 6L6 to do that.
Darlingtom pair connection will reduce this drive current.
But I just use mosfets, because their gate drive is high impedance, like a
tube.

The down side is that mosfets have high input capacitance, but using
appropriate low impedance drive circuitry to achieve a
high time constant for the RC involved solves that problem.


Patrick Turner.



Regards,

John Andreen

John Andreen wrote:

Patrick,

Thanks again for all the wonderful insight.

I would love to provide a schematic, but I do not know the legalities
involved. It is in fact intellectual property of a
rather large audio company. They have deep pockets and mean lawyers. Trust
me on this, I know whom they have
litigated and sent into the depths of oblivion. I was only given a copy of
the schematic out of friendship and on the
condition that I won't reveal it. It could also compromise my friend and
his position. As a side note, this companies Non-Disclosure agreement is 28
pages of legalistic mumbo jumbo and folderol. I can however, publish a
schematic of my modified design when I am completed or near completion. I
must be able to show that this is my own design, complete with a minimum of
7 unique differences. This is really why I am asking some of the questions
that I ask. Slowly but surely identifying the *major* design flaws and then
creating my own circuits to hopefully correct them. I may know much about
silicon audio, but I am for sure a plebe at vacuum tubes.

When I get home, I will check the schematic and count the output devices.
Just from memory, I am certain that there are at least 6 sets of
complementary pairs. Car audio is really a harsh environment to design
for( this is not the case for my design, as I want to drive my Apogee's at
home). Most output devices are operated at a maximum heatsink temperature
of about 90 degrees C. So taking into account device derating, it is rather
common to use an excess of output devices. And, in a car, it could be in
Gnome, Alaska one day and in Death Valley the next.

Currently, I am still working on the PS sections. This includes the tube
heaters, the +/- 300 volt rails for the tubes, +/- 18 volt rails for the
rails for the output BJT's, and the +/- 15 volt rails for the support
circuitry. Haven't made it to the audio sections yet. Hell, I am still
having a tough time understanding that there is only 1 kind of tube and not
P and N tubes like transistors.

There's the quasi-complementary style circuit, with two tubes stacked
totem pole
style. Something like
http://headwize2.powerpill.org/proje...=cmoy5_prj.htm
figure 1
You could change things so the bottom tube's cathode circuit is fed by a
negative
power supply, and the top tube's plate circuit fed by a positive power
supply. And
the top tube's grid tied to ground thru a 500K resistor. You wouldn't
use this exact
circuit, as you want more power and low impedance. But this topology
should suggest
possibilities.

David R Brooks wrote in
:

For *real* B+ power in a car, why not a 3-phase transformer fed direct
from the alternator?


That solution is a bit expensive as 3 phase outputs are rather rare on
automotive alternators. Another factor is that most automotive
alternators will cook themselves if constant high current demands are made
on them. Now if you add a truck alternator modified with 3 phase outputs,
that might resolve the reliability issue, but the voltage will vary quite
a bit so regulation is a must. When all is said and done, you might as
well put a honda generator in the trunk/boot. It would be cheaper and
probably better.

r




Robert Casey wrote:
[snip]
:But you need to have a DC-DC converter from 12V to the B+ you need at
the
:current you need. A switchmode supply operating around 100KHz
frequency to avoid noise in the audio, also no beat frequencies from
audio and 100KHz
:invading the audio spectrum).





--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

Simpleton question:

What is JPT?????????
jack

j wrote:

Simpleton question:

What is JPT?????????
jack

Don't know, and can't even find it in the original post.

acronymfinder.com gives a few possibilities, like "Joint Project Team",
but none that seem to fit into the context of this thread.

Cheers,
Fre

--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

j wrote:

Simpleton question:

What is JPT?????????
jack






You must mean "BJT". That's "Bipolar Junction transistor", AKA NPN and PNP
transistors. As opposed to FETs.....

I am not sure why it is not yet being done? But, I was discussing something
along the same lines with a gentleman at a computer swap I sell at. It goes
like this.

Right now there are private companys as well as our government looking to
make a motor/generator for use in 3rd world countries and probably military
use. The idea is to use a 3-phase brushless DC motor to spin up a small
turbine engine so that they can be started. Typically 30,000 + rpm. Meter
in whatever fuel you got laying around, say propane. Viola, you now have an
operational turbine. Now, use the starter motor as a 3 phase generator.
You now have lots of available power. I was working with a company that was
Engineering a 3 phase brushless for just this task. I thought it would be a
great idea for car audio needs. Alas, the price is quite steep.

The gentleman and I went on to discuss the application of doing it with an
alternator.

Most of the car audio SMPS I had a hand in were mostly operated at under 40
kHz. Switching losses in the ferrite core and the MOSFET drivers almost
make you keep your frequency low. The higher the frequency, the higher the
losses, especially in high current supplies. There is also higher noise
induced when the rectifying diodes conduct and recovers as frequency
increases. Where I used to work, we did make 1 or 2 smaller amplifiers that
were switching at 60-80 kHz. They worked quite well. I have seen poorly
designed amplifiers that you can indeed hear the sum and difference beating
of the audio/SMPS. We called it "swizzle"

I personally would like to make a power supply using IGBT's switching at 75
kHz or higher. It will also take a better grade of ferrite for the core
matl.

Good info,

John Andreen


"David R Brooks" wrote in message
...
For *real* B+ power in a car, why not a 3-phase transformer fed direct
from the alternator?

Robert Casey wrote:
[snip]
:But you need to have a DC-DC converter from 12V to the B+ you need at the
:current you need. A switchmode supply operating around 100KHz
frequency to avoid noise in the audio, also no beat frequencies from
audio and 100KHz
:invading the audio spectrum).

Thanks for the info,

I checked the schematic, there are 8 pairs of complementary sets. I have
decided that I will post at least the output section of the schematic. I
have to scan in from paper and do recognition. Clean it up a bit to remove
any bits that might cause legalities. That way you all can have a look and
see. Okay? I am an Engineer and not to afraid to share knowledge and
ideas. I guess that is really what a forum is all about. I have however
worked with those who would not tell another a single thing. Shouldn't be
more than a few days before I post it. Any ideas on how to do this
properly? Should I place it on my personal web space and provide a pointer?

About the schematic, I still don't understand just what configuration the
output drivers are in. When I get it up there maybe someone can tell me.
SS is butter to me, Valves are still a conondrum.

Regards,

John Andreen




"Robert Casey" wrote in message
...
John Andreen wrote:

Patrick,

Thanks again for all the wonderful insight.

I would love to provide a schematic, but I do not know the legalities
involved. It is in fact intellectual property of a
rather large audio company. They have deep pockets and mean lawyers.
Trust
me on this, I know whom they have
litigated and sent into the depths of oblivion. I was only given a copy
of
the schematic out of friendship and on the
condition that I won't reveal it. It could also compromise my friend and
his position. As a side note, this companies Non-Disclosure agreement is
28
pages of legalistic mumbo jumbo and folderol. I can however, publish a
schematic of my modified design when I am completed or near completion.
I
must be able to show that this is my own design, complete with a minimum
of
7 unique differences. This is really why I am asking some of the
questions
that I ask. Slowly but surely identifying the *major* design flaws and
then
creating my own circuits to hopefully correct them. I may know much
about
silicon audio, but I am for sure a plebe at vacuum tubes.

When I get home, I will check the schematic and count the output devices.
Just from memory, I am certain that there are at least 6 sets of
complementary pairs. Car audio is really a harsh environment to design
for( this is not the case for my design, as I want to drive my Apogee's
at
home). Most output devices are operated at a maximum heatsink
temperature
of about 90 degrees C. So taking into account device derating, it is
rather
common to use an excess of output devices. And, in a car, it could be in
Gnome, Alaska one day and in Death Valley the next.

Currently, I am still working on the PS sections. This includes the tube
heaters, the +/- 300 volt rails for the tubes, +/- 18 volt rails for the
rails for the output BJT's, and the +/- 15 volt rails for the support
circuitry. Haven't made it to the audio sections yet. Hell, I am still
having a tough time understanding that there is only 1 kind of tube and
not
P and N tubes like transistors.

There's the quasi-complementary style circuit, with two tubes stacked
totem pole
style. Something like
http://headwize2.powerpill.org/proje...=cmoy5_prj.htm
figure 1
You could change things so the bottom tube's cathode circuit is fed by a
negative
power supply, and the top tube's plate circuit fed by a positive power
supply. And
the top tube's grid tied to ground thru a 500K resistor. You wouldn't
use this exact
circuit, as you want more power and low impedance. But this topology
should suggest
possibilities.

On Tue, 21 Oct 2003 21:12:00 -0700, the highly esteemed John Andreen
enlightened us with these pearls of wisdom:

snip

About the schematic, I still don't understand just what configuration the
output drivers are in. When I get it up there maybe someone can tell me.
SS is butter to me, Valves are still a conondrum.

The best analogy to SS for a tube is an n-channel depletion mode JFET.
Electrode-wise, source=cathode, drain=plate(or anode), and gate=grid.
Tetrodes and pentodes also have a screen grid, which has no SS equivalent,
and pentodes also have a suppressor which may or may not be internally
connected (it is in most, but not all pentodes). Again, these have no true
SS equivalent. However, as far as circuit configurations the screen and
suppressor do not usually influence its type (unless it is used as a
control electrode - normally they are used at a fixed potential).

The above being the case, you can use a tube in any circuit which you can
use an n-channel depletion mode JFET. This includes common cathode,
common grid, common plate (cathode follower) for a simple single-device
configuration. Multiple devices can be cascades, cascodes, differential
pairs, etc.

If you want to post your schematic to a newsgroup, don't do it here. The
"official" place is alt.binaries.schematics.electronic (you will sometimes
see the acronym ABSE, which refers to that group). Otherwise, putting
it on a website and posting the URL here is fine as well.

--
Greg

--The software said it requires Win2000 or better, so I installed Linux.

Thanks for all the help,

I think I will place the schematic on my homepage/website. Gotta set it up
first as I am a new subscriber to cox hi speed
internet. Maybe I will just place it in my "space" and point to it. Almost
done with cleaning it up so that I can post it.

Smart man you are running Linux. It is by far and away my most favorite OS.
Mac's are next, though my 7710/180 is outdated and won't run OSX without
processor card. Sadly, I am writing this on WinXP.

Regards,

John Andreen
"Greg Pierce" wrote in message
news
On Tue, 21 Oct 2003 21:12:00 -0700, the highly esteemed John Andreen
enlightened us with these pearls of wisdom:

snip

About the schematic, I still don't understand just what configuration
the
output drivers are in. When I get it up there maybe someone can tell
me.
SS is butter to me, Valves are still a conondrum.

The best analogy to SS for a tube is an n-channel depletion mode JFET.
Electrode-wise, source=cathode, drain=plate(or anode), and gate=grid.
Tetrodes and pentodes also have a screen grid, which has no SS equivalent,
and pentodes also have a suppressor which may or may not be internally
connected (it is in most, but not all pentodes). Again, these have no true
SS equivalent. However, as far as circuit configurations the screen and
suppressor do not usually influence its type (unless it is used as a
control electrode - normally they are used at a fixed potential).

The above being the case, you can use a tube in any circuit which you can
use an n-channel depletion mode JFET. This includes common cathode,
common grid, common plate (cathode follower) for a simple single-device
configuration. Multiple devices can be cascades, cascodes, differential
pairs, etc.

If you want to post your schematic to a newsgroup, don't do it here. The
"official" place is alt.binaries.schematics.electronic (you will sometimes
see the acronym ABSE, which refers to that group). Otherwise, putting
it on a website and posting the URL here is fine as well.

--
Greg

--The software said it requires Win2000 or better, so I installed Linux.