Re: [Drakelist] AC-4 (bias mod)

2012-01-21 Thread Garey Barrell
he bias for SSB (or AM), just for CW (and
real FSK).

So, you would need a switch or relay added and USE it to change modes.
Yes,
bias it past cut-off, will result in no emission between code elements,
but also over
part of the cycle.

Key clicks could be delt with...  The reason they had key clicks was
primarily because
they were cathode keying high voltages with no shaping as I recall. no?
Bias is only
on the finals, we don't key those or do we?

Junk?  Isn't our driver pretty clean?  If not, wouldn't we have the same
spurs and junk
with a linear final?

We DO have a tuned output tank circuit for the flywheel effect... no?

BUT, if we don't have enough (voltage) drive, that might be a problem, but
we don't
really need full power...

Don't ya think?  Changing bias for CW wasn't my idea, but it did sound
good to me.
TIA, I am trying to learn here...  There probably IS some reason nobody
did this
originally!

73,
Gary
WB6OGD


- Original Message -
From: Garey Barrell
To: Gary Winblad
Cc: drakelist
Sent: Fri, 20 Jan 2012 15:31:44 - (UTC)
Subject: Re: [Drakelist] AC-4  (bias mod)

Gary -

In a word  NO.

The PA stage is operated as a LINEAR amplifier, Class AB1, meaning the
output signal is a reasonable
facsimile of the input signal.  The BIAS voltage is carefully chosen to
'center' the operation of
the amplifier in the linear portion of the tube's operating region.

Increasing the BIAS voltage WILL reduce the IDLE current, (between code
elements,) but will shift
the PA to a non-linear region.  This will result in distortion of the
signal, with the potential of
spurious signals, clicks, and other 'junk'. This is one reason clicks were
so prevalent in the older
transmitters. A true Class C amplifier requires considerably more driving
power, and relies on the
'flywheel effect' of it's output network to 'smooth' out the 'pulses' of
drive that exceed the bias
potential.

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs



Gary Winblad wrote:

All this talk of rebuilding AC-4 supplies had me thinking...

I have seen a mod(?) that said to turn up(down?) the bias when running
CW
(and FSK?) to set the finals more to Class C operation to save power
dissipation.

Is this a good idea?  Wouldn't it be easy to add a switch or relay and
another potentiometer while you are in there rebuilding?

73,
Gary
WB6OGD



___
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist


Re: [Drakelist] AC-4 (bias mod)

2012-01-20 Thread Dennis Monticelli
Guess I'll just toss in my 2 cents worth.

Converting a Drake to class C in CW mode only by simply changing the
bias of the PA may not be a good idea depending upon how it is driven
and to a lesser extent how much Q and harmonic filtering is in the
tank circuitry.  I have not studied the schematic so I'll just leave
it at that.  But I really don't think class C operation in general
should get a bad rap.  It's a perfectly legit class of operation and
like any mode there is a right way and a wrong way to implement it.
It has a major advantage in terms of improving efficiency and thus
reduction of heat in the finals.  I have measured my Viking II PA with
good instrumentation at 79 to 80% over the core bands on multiple
occasions.  We're talking 144W out for 180W in. The final is parallel
6146's, fixed plus drive-induced bias, and a heavy duty tank with
continously optimized Q due to slaving a rollerducter to the plate
tuning cap.  As for driving power, you generally need a little more
with class C, but not a lot more (assuming beam power tubes and
assuming we're talking CW, not plate mod AM).   To control clicks one
should shape the drive signal shoulders softer than what one would
normally do when driving a linear amp because the turn-on and turn-off
characteristic of class C is more abrupt.

There is nothing fundamentally wrong with class C for CW.  In fact
some cell phones use it.  I think modern rigs avoid it simply because
the PA is already linear for other reasons and already has a fan to
get rid of heat.  The maker would have to design the driver stage a
little differently and the antenna coupling circuitry as well.  I
guess that is not worth adverstising additional 10's of watts of CW
output power on the brochure.

Dennis AE6C


On 1/20/12, Garey Barrell  wrote:
> Gary -
>
> Obviously the bias would remain in the Class AB1 area for SSB and AM.
>
> Applying a keyed signal to a non-linear amplifier is a bad idea.  Every time
> the drive is started or
> stopped there is the opportunity for additional distortion products to be
> generated.  Some SSB
> distortion is caused by biasing the amplifier too high or too low, resulting
> in 'compression' or
> limiting the waveform to less than it's peak.  More distortion.
>
> Perhaps we have an amplifier expert on here who can definitively respond to
> your question.  There
> are no doubt MANY reasons why all transmitters switched to linear operation
> for CW, in spite of the
> 'power/efficiency savings.  If nothing else than it takes large amounts of
> drive POWER, more
> trouble, including greatly increased Grid dissipation.
>
> To me, turning an input signal on and off to a Class C amplifier is asking
> for trouble.  A Class C
> amplifier is essentially a switch, ON or OFF, and relies on the Q of the
> tank circuits to 'smooth
> things out'.  A lot of potential headaches for a few percent efficiency
> increase.
>
> There are LOTS of 'ideas' on the internet that 'sound' good  :-)
>
> Let us know what you find out!!
>
> 73, Garey - K4OAH
> Glen Allen, VA
>
> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
> and TR-4/C Service Supplement CDs
> 
>
>
> Gary Winblad wrote:
>> Well yeahh  Garey
>>
>> I am not suggesting we change the bias for SSB (or AM), just for CW (and
>> real FSK).
>>
>> So, you would need a switch or relay added and USE it to change modes.
>> Yes,
>> bias it past cut-off, will result in no emission between code elements,
>> but also over
>> part of the cycle.
>>
>> Key clicks could be delt with...  The reason they had key clicks was
>> primarily because
>> they were cathode keying high voltages with no shaping as I recall. no?
>> Bias is only
>> on the finals, we don't key those or do we?
>>
>> Junk?  Isn't our driver pretty clean?  If not, wouldn't we have the same
>> spurs and junk
>> with a linear final?
>>
>> We DO have a tuned output tank circuit for the flywheel effect... no?
>>
>> BUT, if we don't have enough (voltage) drive, that might be a problem, but
>> we don't
>> really need full power...
>>
>> Don't ya think?  Changing bias for CW wasn't my idea, but it did sound
>> good to me.
>> TIA, I am trying to learn here...  There probably IS some reason nobody
>> did this
>> originally!
>>
>> 73,
>> Gary
>> WB6OGD
>>
>>
>> - Original Message -
>> From: Garey Barrell 
>> To: Gary Winblad 
>> Cc: drakelist 
>> Sent: Fri, 20 Jan 2012 15:31:44 - (UTC)
>> Subject: Re: [Drakelist] AC-4  (bias mod)
>>
>> Gary -
>>
>

Re: [Drakelist] AC-4 (bias mod)

2012-01-20 Thread Gary Winblad
Hi Garey,
Thanks, good explanation.
I'm not going to try it any time soon  ;-)
73,
Gary

- Original Message -
From: Garey Barrell 
To: Gary Winblad 
Cc: drakelist 
Sent: Fri, 20 Jan 2012 23:24:40 - (UTC)
Subject: Re: [Drakelist] AC-4  (bias mod)

Gary -

Obviously the bias would remain in the Class AB1 area for SSB and AM.

Applying a keyed signal to a non-linear amplifier is a bad idea.  Every time 
the drive is started or 
stopped there is the opportunity for additional distortion products to be 
generated.  Some SSB 
distortion is caused by biasing the amplifier too high or too low, resulting in 
'compression' or 
limiting the waveform to less than it's peak.  More distortion.

Perhaps we have an amplifier expert on here who can definitively respond to 
your question.  There 
are no doubt MANY reasons why all transmitters switched to linear operation for 
CW, in spite of the 
'power/efficiency savings.  If nothing else than it takes large amounts of 
drive POWER, more 
trouble, including greatly increased Grid dissipation.

To me, turning an input signal on and off to a Class C amplifier is asking for 
trouble.  A Class C 
amplifier is essentially a switch, ON or OFF, and relies on the Q of the tank 
circuits to 'smooth 
things out'.  A lot of potential headaches for a few percent efficiency 
increase.

There are LOTS of 'ideas' on the internet that 'sound' good  :-)

Let us know what you find out!!

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs



Gary Winblad wrote:
> Well yeahh  Garey
>
> I am not suggesting we change the bias for SSB (or AM), just for CW (and real 
> FSK).
>
> So, you would need a switch or relay added and USE it to change modes.  Yes,
> bias it past cut-off, will result in no emission between code elements, but 
> also over
> part of the cycle.
>
> Key clicks could be delt with...  The reason they had key clicks was 
> primarily because
> they were cathode keying high voltages with no shaping as I recall. no?  Bias 
> is only
> on the finals, we don't key those or do we?
>
> Junk?  Isn't our driver pretty clean?  If not, wouldn't we have the same 
> spurs and junk
> with a linear final?
>
> We DO have a tuned output tank circuit for the flywheel effect... no?
>
> BUT, if we don't have enough (voltage) drive, that might be a problem, but we 
> don't
> really need full power...
>
> Don't ya think?  Changing bias for CW wasn't my idea, but it did sound good 
> to me.
> TIA, I am trying to learn here...  There probably IS some reason nobody did 
> this
> originally!
>
> 73,
> Gary
> WB6OGD
>
>
> - Original Message -
> From: Garey Barrell 
> To: Gary Winblad 
> Cc: drakelist 
> Sent: Fri, 20 Jan 2012 15:31:44 - (UTC)
> Subject: Re: [Drakelist] AC-4  (bias mod)
>
> Gary -
>
> In a word  NO.
>
> The PA stage is operated as a LINEAR amplifier, Class AB1, meaning the output 
> signal is a reasonable
> facsimile of the input signal.  The BIAS voltage is carefully chosen to 
> 'center' the operation of
> the amplifier in the linear portion of the tube's operating region.
>
> Increasing the BIAS voltage WILL reduce the IDLE current, (between code 
> elements,) but will shift
> the PA to a non-linear region.  This will result in distortion of the signal, 
> with the potential of
> spurious signals, clicks, and other 'junk'. This is one reason clicks were so 
> prevalent in the older
> transmitters. A true Class C amplifier requires considerably more driving 
> power, and relies on the
> 'flywheel effect' of it's output network to 'smooth' out the 'pulses' of 
> drive that exceed the bias
> potential.
>
> 73, Garey - K4OAH
> Glen Allen, VA
>
> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
> and TR-4/C Service Supplement CDs
>
>
>
> Gary Winblad wrote:
> > All this talk of rebuilding AC-4 supplies had me thinking...
> >
> > I have seen a mod(?) that said to turn up(down?) the bias when running CW
> > (and FSK?) to set the finals more to Class C operation to save power
> > dissipation.
> >
> > Is this a good idea?  Wouldn't it be easy to add a switch or relay and
> > another potentiometer while you are in there rebuilding?
> >
> > 73,
> > Gary
> > WB6OGD
> > http://mailman.zerobeat.net/mailman/listinfo/drakelist
>

___
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist


Re: [Drakelist] AC-4 (bias mod)

2012-01-20 Thread Richard Knoppow


- Original Message - 
From: "Garey Barrell" 

To: "Gary Winblad" 
Cc: "drakelist" 
Sent: Friday, January 20, 2012 3:24 PM
Subject: Re: [Drakelist] AC-4 (bias mod)



Gary -

Obviously the bias would remain in the Class AB1 area for 
SSB and AM.


Applying a keyed signal to a non-linear amplifier is a bad 
idea.  Every time the drive is started or stopped there is 
the opportunity for additional distortion products to be 
generated.  Some SSB distortion is caused by biasing the 
amplifier too high or too low, resulting in 'compression' 
or limiting the waveform to less than it's peak.  More 
distortion.


Perhaps we have an amplifier expert on here who can 
definitively respond to your question.  There are no doubt 
MANY reasons why all transmitters switched to linear 
operation for CW, in spite of the 'power/efficiency 
savings.  If nothing else than it takes large amounts of 
drive POWER, more trouble, including greatly increased 
Grid dissipation.


To me, turning an input signal on and off to a Class C 
amplifier is asking for trouble.  A Class C amplifier is 
essentially a switch, ON or OFF, and relies on the Q of 
the tank circuits to 'smooth things out'.  A lot of 
potential headaches for a few percent efficiency increase.


There are LOTS of 'ideas' on the internet that 'sound' 
good  :-)


Let us know what you find out!!

73, Garey - K4OAH
Glen Allen, VA



   There is a lot more than changing bias to converting a 
linear amplifier of any class to a Class-C amplifier. For 
one thing the plate impedance and thus tank requirements 
will be different. Its not trivial. There is a lot of 
information on designing Class-C amps in older handbooks, 
maybe even on the web, although I have not looked. The 
difference in output for a tube with given plate dissipation 
can be considerable. A Class AB linear has less than 66% 
efficiency and a Class-C amp around 78% (can be made higher 
with special tank circuits).
   Essentially, Class-C amplifiers are pulse integration 
devices. The plate efficiency is partly a matter of the 
pulse duration. I think if you want a transmitter primarily 
for CW or FSK building one from scratch might be best.



--
Richard Knoppow
Los Angeles
WB6KBL
dickb...@ix.netcom.com 



___
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist


Re: [Drakelist] AC-4 (bias mod)

2012-01-20 Thread Garey Barrell

Gary -

Obviously the bias would remain in the Class AB1 area for SSB and AM.

Applying a keyed signal to a non-linear amplifier is a bad idea.  Every time the drive is started or 
stopped there is the opportunity for additional distortion products to be generated.  Some SSB 
distortion is caused by biasing the amplifier too high or too low, resulting in 'compression' or 
limiting the waveform to less than it's peak.  More distortion.


Perhaps we have an amplifier expert on here who can definitively respond to your question.  There 
are no doubt MANY reasons why all transmitters switched to linear operation for CW, in spite of the 
'power/efficiency savings.  If nothing else than it takes large amounts of drive POWER, more 
trouble, including greatly increased Grid dissipation.


To me, turning an input signal on and off to a Class C amplifier is asking for trouble.  A Class C 
amplifier is essentially a switch, ON or OFF, and relies on the Q of the tank circuits to 'smooth 
things out'.  A lot of potential headaches for a few percent efficiency increase.


There are LOTS of 'ideas' on the internet that 'sound' good  :-)

Let us know what you find out!!

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs



Gary Winblad wrote:

Well yeahh  Garey

I am not suggesting we change the bias for SSB (or AM), just for CW (and real 
FSK).

So, you would need a switch or relay added and USE it to change modes.  Yes,
bias it past cut-off, will result in no emission between code elements, but 
also over
part of the cycle.

Key clicks could be delt with...  The reason they had key clicks was primarily 
because
they were cathode keying high voltages with no shaping as I recall. no?  Bias 
is only
on the finals, we don't key those or do we?

Junk?  Isn't our driver pretty clean?  If not, wouldn't we have the same spurs 
and junk
with a linear final?

We DO have a tuned output tank circuit for the flywheel effect... no?

BUT, if we don't have enough (voltage) drive, that might be a problem, but we 
don't
really need full power...

Don't ya think?  Changing bias for CW wasn't my idea, but it did sound good to 
me.
TIA, I am trying to learn here...  There probably IS some reason nobody did this
originally!

73,
Gary
WB6OGD


- Original Message -
From: Garey Barrell 
To: Gary Winblad 
Cc: drakelist 
Sent: Fri, 20 Jan 2012 15:31:44 - (UTC)
Subject: Re: [Drakelist] AC-4  (bias mod)

Gary -

In a word  NO.

The PA stage is operated as a LINEAR amplifier, Class AB1, meaning the output 
signal is a reasonable
facsimile of the input signal.  The BIAS voltage is carefully chosen to 
'center' the operation of
the amplifier in the linear portion of the tube's operating region.

Increasing the BIAS voltage WILL reduce the IDLE current, (between code 
elements,) but will shift
the PA to a non-linear region.  This will result in distortion of the signal, 
with the potential of
spurious signals, clicks, and other 'junk'. This is one reason clicks were so 
prevalent in the older
transmitters. A true Class C amplifier requires considerably more driving 
power, and relies on the
'flywheel effect' of it's output network to 'smooth' out the 'pulses' of drive 
that exceed the bias
potential.

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs



Gary Winblad wrote:
> All this talk of rebuilding AC-4 supplies had me thinking...
>
> I have seen a mod(?) that said to turn up(down?) the bias when running CW
> (and FSK?) to set the finals more to Class C operation to save power
> dissipation.
>
> Is this a good idea?  Wouldn't it be easy to add a switch or relay and
> another potentiometer while you are in there rebuilding?
>
> 73,
> Gary
> WB6OGD
> http://mailman.zerobeat.net/mailman/listinfo/drakelist



___
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist


Re: [Drakelist] AC-4 (bias mod)

2012-01-20 Thread Gary Winblad
Well yeahh  Garey

I am not suggesting we change the bias for SSB (or AM), just for CW (and real 
FSK).

So, you would need a switch or relay added and USE it to change modes.  Yes,
bias it past cut-off, will result in no emission between code elements, but 
also over
part of the cycle.

Key clicks could be delt with...  The reason they had key clicks was primarily 
because
they were cathode keying high voltages with no shaping as I recall. no?  Bias 
is only
on the finals, we don't key those or do we?

Junk?  Isn't our driver pretty clean?  If not, wouldn't we have the same spurs 
and junk
with a linear final?

We DO have a tuned output tank circuit for the flywheel effect... no?

BUT, if we don't have enough (voltage) drive, that might be a problem, but we 
don't
really need full power...

Don't ya think?  Changing bias for CW wasn't my idea, but it did sound good to 
me.
TIA, I am trying to learn here...  There probably IS some reason nobody did this
originally!

73,
Gary
WB6OGD


- Original Message -
From: Garey Barrell 
To: Gary Winblad 
Cc: drakelist 
Sent: Fri, 20 Jan 2012 15:31:44 -0000 (UTC)
Subject: Re: [Drakelist] AC-4  (bias mod)

Gary -

In a word  NO.

The PA stage is operated as a LINEAR amplifier, Class AB1, meaning the output 
signal is a reasonable 
facsimile of the input signal.  The BIAS voltage is carefully chosen to 
'center' the operation of 
the amplifier in the linear portion of the tube's operating region.

Increasing the BIAS voltage WILL reduce the IDLE current, (between code 
elements,) but will shift 
the PA to a non-linear region.  This will result in distortion of the signal, 
with the potential of 
spurious signals, clicks, and other 'junk'. This is one reason clicks were so 
prevalent in the older 
transmitters. A true Class C amplifier requires considerably more driving 
power, and relies on the 
'flywheel effect' of it's output network to 'smooth' out the 'pulses' of drive 
that exceed the bias 
potential.

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs



Gary Winblad wrote:
> All this talk of rebuilding AC-4 supplies had me thinking...
>
> I have seen a mod(?) that said to turn up(down?) the bias when running CW
> (and FSK?) to set the finals more to Class C operation to save power
> dissipation.
>
> Is this a good idea?  Wouldn't it be easy to add a switch or relay and
> another potentiometer while you are in there rebuilding?
>
> 73,
> Gary
> WB6OGD
> http://mailman.zerobeat.net/mailman/listinfo/drakelist 

___
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist


Re: [Drakelist] AC-4 (bias mod)

2012-01-20 Thread Garey Barrell

Gary -

In a word  NO.

The PA stage is operated as a LINEAR amplifier, Class AB1, meaning the output signal is a reasonable 
facsimile of the input signal.  The BIAS voltage is carefully chosen to 'center' the operation of 
the amplifier in the linear portion of the tube's operating region.


Increasing the BIAS voltage WILL reduce the IDLE current, (between code elements,) but will shift 
the PA to a non-linear region.  This will result in distortion of the signal, with the potential of 
spurious signals, clicks, and other 'junk'. This is one reason clicks were so prevalent in the older 
transmitters. A true Class C amplifier requires considerably more driving power, and relies on the 
'flywheel effect' of it's output network to 'smooth' out the 'pulses' of drive that exceed the bias 
potential.


73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs



Gary Winblad wrote:

All this talk of rebuilding AC-4 supplies had me thinking...

I have seen a mod(?) that said to turn up(down?) the bias when running CW
(and FSK?) to set the finals more to Class C operation to save power
dissipation.

Is this a good idea?  Wouldn't it be easy to add a switch or relay and
another potentiometer while you are in there rebuilding?

73,
Gary
WB6OGD
http://mailman.zerobeat.net/mailman/listinfo/drakelist 


___
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist


Re: [Drakelist] AC-4 (bias mod)

2012-01-20 Thread Gary Winblad
All this talk of rebuilding AC-4 supplies had me thinking...

I have seen a mod(?) that said to turn up(down?) the bias when running CW
(and FSK?) to set the finals more to Class C operation to save power
dissipation.

Is this a good idea?  Wouldn't it be easy to add a switch or relay and
another potentiometer while you are in there rebuilding?

73,
Gary
WB6OGD


- Original Message -
From: Mark Pilant 
To: drakelist 
Sent: Fri, 20 Jan 2012 01:52:42 - (UTC)
Subject: Re: [Drakelist] AC-4

Hi John.

That I've always done, as suggested by others, is to replace the two
conductor cord with a more modern grounded plug and wire.  You can
see the one I used in the AC-4 rebuild I describe here:

 http://www.n1vqw.net/ac4rebuild/

BTW, it is a standard "computer" cord, and I cut off the female end
with about 6 inches of cord in case I ever want to use it.

73

- Mark  N1VQW

___
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist
___
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist