Why plate degeneration in a cathode follower?

[Robert Baer]

What is the benefit of adding plate degeneration in a cathode follower?
All i see is that it decreases the follower gain, say from 95% to 90%.

 

[Tim Williams]

At least for a triode... should be almost zero effect for a pentode (if
the screen doesn't also connect below the resistor).

Same thing a collector resistor does on a BJT follower -- dampens the
common-collector oscillation mode. Base/grid/gate stopper is more
traditional though, better efficiency.

Tim

 

[Robert Baer]

At least for a triode... should be almost zero effect for a pentode (if
the screen doesn't also connect below the resistor).

Same thing a collector resistor does on a BJT follower -- dampens the
common-collector oscillation mode. Base/grid/gate stopper is more
traditional though, better efficiency.

Tim

? Common collector?
The device i am fixing has triodes (a number of 6SN7s to be more
specific) and every cathode follower has a 10K resistor in the plate, NO
pickoff for phase splitter-type use.

The plate resistor reduces the cathode follower gain, and i do not
think that it could possibly reduce distortion...it might even increase
the distortion (K-A voltage varies more).

...Now if usage was as inverter and resistor was added in the cathode,
again the gain would be reduced but the distortion also would be reduced
(less G-K resultant drive).

 

[Adrian Tuddenham]

? Common collector?
The device i am fixing has triodes (a number of 6SN7s to be more
specific) and every cathode follower has a 10K resistor in the plate, NO
pickoff for phase splitter-type use.

[...]

1) Equalising load currents between several valves in parallel without a
significant increase in output impedance?

2) Peak current protection in the event of an inter-electrode short or
other abnormal operating conditions?

3) Reducing the difference in the output impedance between positive and
negative half-cycles so as to avoid high frequency rectification effects
due to charging and discharging the cathode-heater capacitance?

 

[Rocky]

? Common collector?
The device i am fixing has triodes (a number of 6SN7s to be more
specific) and every cathode follower has a 10K resistor in the plate, NO
pickoff for phase splitter-type use.

The plate resistor reduces the cathode follower gain, and i do not
think that it could possibly reduce distortion...it might even increase
the distortion (K-A voltage varies more).

The plate resistor increases the Miller Effect which causes HF roll off.

 

[Robert Baer]

What's the cathode load? Maybe post a schematic?

...Jim Thompson

...Please wait; my access to my site is down temporarily.

 

[Robert Baer]

What? What? Is the Joerg "flu" spreading ?>:-}

...Jim Thompson

For the PDF, find it at http://www.oil4lessllc.org/635/

 

[Tim Williams]

I do believe... I see phase-splitting >:-}

Can't you _simulate_ that ?

Come on Jim, ain't your rusty ol' brain remember this stuff?

If Robert's referring to V2, they aren't doing anything helpful.

Very old circuit. Mine has "Eico" painted on it, but uses 6K6s for the
higher power bits. 6X4? Gah, a submini in an octal set... what an
abomination

Tim

 

[Robert Baer]

Come on Jim, ain't your rusty ol' brain remember this stuff?

If Robert's referring to V2, they aren't doing anything helpful.

Very old circuit. Mine has "Eico" painted on it, but uses 6K6s for the
higher power bits. 6X4? Gah, a submini in an octal set... what an
abomination

Tim

....but...it is an AN-TEEK!

 

[Tauno Voipio]

I found the PDF, I was just musing about who couldn't access it.

Your "was/now" and arrows are confusing. Who's on first ?

...Jim Thompson

He's preparing to grill the final tube pair, the cathode bias is
destroyed by moving the grid resistor low ends, and the plate
current protection resistors are shorted.

The oscillator quality is compromised by moving the output
tap from the buffer to the feedback line, and the buffer
isolation is compromised by adding the cathode bypass.

Hope he has spare tubes ...

 

[Robert Baer]

I found the PDF, I was just musing about who couldn't access it.

Your "was/now" and arrows are confusing. Who's on first ?

...Jim Thompson

The "X" indicates where i broke a connection, the arrows show a new
connection (eg: move grid resistor from ground to cathode), and adding
the jumpers put across the 10K plate degeneration resistors.

Lastly, the arrows show that the wire from the sine/square/pulse
switch was moved from the divider to the (other) plate.
Maybe i should experiment trying V5A instead of V5B plate for even
greater overdrive (level was 6Vpk-pk now 30Vpk-pk; cold be 65Vpk-pk if
used V5A).
PS: Sorry i forgot how the Abbott & Costello joke went..

 

[Robert Baer]

He's preparing to grill the final tube pair, the cathode bias is
destroyed by moving the grid resistor low ends, and the plate
current protection resistors are shorted.

The oscillator quality is compromised by moving the output
tap from the buffer to the feedback line, and the buffer
isolation is compromised by adding the cathode bypass.

Hope he has spare tubes ...

Maybe, but having a signal generator with sine output FIVE TIMES LESS
in amplitude WRT other waveform output selections just ain't kosher.
The CFs do not run any harder than before, the V5A bypass gives more
drive for a better square / "pulse" waveform and has little effect on
the oscillator; V5A is nowhere near to grid or plate glow..

 

[josephkk]

The "X" indicates where i broke a connection, the arrows show a new
connection (eg: move grid resistor from ground to cathode), and adding
the jumpers put across the 10K plate degeneration resistors.

Lastly, the arrows show that the wire from the sine/square/pulse
switch was moved from the divider to the (other) plate.
Maybe i should experiment trying V5A instead of V5B plate for even
greater overdrive (level was 6Vpk-pk now 30Vpk-pk; cold be 65Vpk-pk if
used V5A).
PS: Sorry i forgot how the Abbott & Costello joke went..

For anybody that is interested:

http://www.baseball-almanac.com/humor4.shtml

First find of course.

?-)

 

[Robert Baer]

Maybe we could start by defining WHAT is it supposed to do? ....
spelling out GOZINTA/GOZOUTA.

(I actually have made three parts for PSpice: GOZINTA, GOZOUTA and
GOZBI

...Jim Thompson

Sorry, i do not live in the PLAINs area of the US; i live in WA.
Itza signal generator; selectable output sine, square, pulse.

 

[Tauno Voipio]

Well? Describe how it's supposed to work... this switch position does
this, etc., and the output is WHERE?

...Jim Thompson

The OP could start by restoring the switch labels (and tube envelopes)
in the schematic.

 

[Robert Baer]

Well? Describe how it's supposed to work... this switch position does
this, etc., and the output is WHERE?

...Jim Thompson

I give up; if you cannot read a schematic..

 

[Don Lancaster]

It's better acted out.

Wasn't The Who on first and Jimi Hendrix on third?

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

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I think Jimi was on Foxy Lady asking Who are you, but that's the
X-rated version.

I think that was The Who. ...or CSI, I can never remember.