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Broskie Cathode Follower - E88cc, 5u4g, buffer, unbalancer, soekris dam1121 dual mono

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Hello,

I'm trying to build a special tube buffer unbalancer, for a dual mono configuration of two dam1121 dacs from soekris. These have the benefit of 1,4V per channel with zero dc current.

The buffer I want to build is a Broskie cathode follower with E288cc tubes.

Basic circuit looks like this from tube cad site: https://www.tubecad.com/2006/08/12/balanced_dac_and_broskie_cathode_follower.png

balanced_dac_and_broskie_cathode_follower.png


Probably this is way too much effort for a buffer but, I want to go a long way with this thing.

What I want (in my head - and I've been trying to figure out the how to's for weeks now) is a power supply with a full wave tube rectifier (e.g. 5u4g) with a choke input power supply w. filter (e.g. Lundahl LL2742/100 in parallel, and a Cap) followed by an anode choke.

Despite that he mismatched input + / - (I think)


I have some basic questions:

1. Where is the anode resistor for the upper valve (half triode)? Is there one needed at all, and can I put a anode choke instead of it? If so, what voltage would you recommend? I'd have a transformer for 320v CT, 250v CT.

2. The lower circuit will not need another anode resistor?

3. Is it so, that the both halfs of the triode see the same Voltage of Ua=Ub/2 and that Ia will be set by my Ug/Ia set point for Kathode resistor?

4. Won't the two 10K resistors (one R gl (grid leak Resistor), and one R gs (grid stopper)) on the diagram will become a voltage divider for the input signal to go down to half it's value? Shouldn't the R gl be before the R gs (from the input views side)

5. Are the two input capacitors really needed?

6. I know, I will have to pull up the heater for to a recommended maximum U fk, but will i have to pull up just the upper one?

7. Have you tried using LT3045 as a modern approach of low noise Heater supply?
 
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Joined 2011
1. Where is the anode resistor for the upper valve (half triode)?
Is there one needed at all?

No.

2. The lower circuit will not need another anode resistor?

No.

3. Is it so, that the both halfs of the triode see the same Voltage of Ua=Ub/2
and that Ia will be set by my Ug/Ia set point for Kathode resistor?

By symmetry, both will have the same Vpk (within tube tolerances).

4. Won't the two 10K resistors (one R gl (grid leak Resistor), and one R gs
(grid stopper)) on the diagram will become a voltage divider for the input
signal to go down to half it's value? Shouldn't the R gl be before the R gs
(from the input views side)

Those are feedback resistors, in an inverting topology, and set an AC gain of unity for each input.

5. Are the two input capacitors really needed?

Yes.

6. I know, I will have to pull up the heater for to a recommended maximum U fk,
but will i have to pull up just the upper one?

Elevating both heaters is ok, if you observe the ratings.
 
Last edited:

PRR

Member
Joined 2003
Paid Member
Did you read John's description? Or just the diagram?

IRRC, he explained it pretty well.

BTW, "cathode followers" generally do not have plate resistors; and sticking one in usually reduces performance. The White Cathode Follower is an exception.
 
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