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Compound amplifier with constant current sources and DC coupling between stages
Compound amplifier with constant current sources and DC coupling between stages
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Old 10th January 2018, 12:10 PM   #1
JR Cho is offline JR Cho  South Korea
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Default Compound amplifier with constant current sources and DC coupling between stages

I found 'Compound amplifier with constant current sources and DC coupling between stages' in TUBECAD Journal. With single IXYS 10M45S or 10M90S I think I may be able to implement simple CCS's. This looks similar issue with CCS's for CCD line amp?

Any comment and advice would be appreciated.

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Old 11th January 2018, 07:13 AM   #2
Alllensoncanon is offline Alllensoncanon
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Compound amplifier with constant current sources and DC coupling between stages
I don't see the two 5K resistors do much other than reducing the constant current output voltage swing by 50V (aka: Increase the drop off voltage by 50V. Other than that, it has the same function without these two resistors. Why put it in?
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Old 12th January 2018, 09:55 PM   #3
Sodacose is offline Sodacose  United States
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Those resistors are there to limit the voltage across the (solid state) CCSs. It's a stepping stone to tube CCSs in the article. Typical TubeCAD compound arrangement madness.

This is from SRPP deconstructed.

The Tube CAD Journal: Mixed Mode Amplifiers
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Old 12th January 2018, 11:29 PM   #4
Hearinspace is offline Hearinspace  Canada
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Compound amplifier with constant current sources and DC coupling between stages
What J.B.'s motivation was I don't know but there are some ideas about added series resistance here.
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Old 13th January 2018, 12:40 AM   #5
Alllensoncanon is offline Alllensoncanon
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Compound amplifier with constant current sources and DC coupling between stages
Quote:
Originally Posted by Sodacose View Post
Those resistors are there to limit the voltage across the (solid state) CCSs.
IXYS 10M45S has a 450V limits. The 50V reduction from the 5K is not needed here.
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Old 13th January 2018, 02:18 AM   #6
JR Cho is offline JR Cho  South Korea
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Hi all,
With or without 5k resistors. Is that okay to connetct directly b/w V1 and V2 without coupling capacitors?
I'm considering to build the circuit 12AU7 as V1 with 10M90S CCS and 6922 as v2 with resistor load (w/o CCS) and also considering capacitor coupling b/w V! and V2 for stable working (I'm not sure interaction b/w V1 and V2 in case of Direct Coupled..).
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Old 13th January 2018, 07:36 AM   #7
Alllensoncanon is offline Alllensoncanon
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Compound amplifier with constant current sources and DC coupling between stages
Quote:
Originally Posted by JR Cho View Post
Is that okay to connect directly b/w V1 and V2 without coupling capacitors?
Yes. All you need to do is adjust V1 plate voltage via the CSS active load and/or V1 cathode resistor such that it equal to the negative bias voltage that you want for V2. In your example schematic that will be 100V for a -2V of V2 grid bias. If you want a -5V bias, you will need to set it to 97V.

Last edited by Alllensoncanon; 13th January 2018 at 07:41 AM.
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Old 13th January 2018, 02:00 PM   #8
Alllensoncanon is offline Alllensoncanon
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Compound amplifier with constant current sources and DC coupling between stages
Quote:
Originally Posted by Alllensoncanon View Post
All you need to do is adjust V1 plate voltage via the CSS active load and/or V1 cathode resistor such that it equal to the negative bias voltage that you want for V2.
More specifically,

1. Replace V2 cathode follower CSS+5K with a 10K resistor. This should yield the ~102V cathode at idle for the 6922.

2. Replace the 200R V1 cathode resistor with a 330R. This will drop the 12AU7 Ip to 6mA from the 10mA Ip of the 6DJ8. This is to retain the -2V Vg bias and the Vp of 100V.

3. Adjust 10M90S CCS R to yield near 6mA "and" the require -2V V2 bias. Note, The -2V bias is more important than the 6mA in this case. 10M90S also needs in circuit adjustment. The data sheet number is only an approximate.

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