• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

White cathode follower analysis and design

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easphyx

easphyx

Member
Joined 2016
PRR said:
100K on 220uFd is a 22 second time constant. To 37%. At turn-on the tube side jumps-up from zero to +150V, and the cap follows, slowly decaying in the 100K. You still have about 1V of DC five time-constants after turn-on... nearly 2 minutes! I'd lean to a much smaller value. Even 10X the load that the cap was figured for audio and nominal load. 2.5K gets you to 1V after 3 seconds.
Click to expand...

Yes, you're right. I forgot such a simple thing as time constant of unloaded output RC circuit looking at frequency response under load only. If I plug in my headphones before output DC voltage dropped down to zero, nothing good will happen...
 
PRR

PRR

Member
Joined 2003
Paid Member
> equality of tubes' plate voltages.

In simulations, and in dumb thinking, it would seem that some distortions cancel when Vpk is the same on both tubes. (Assumes Ik is equal and thus Vgk is equal.)

But this is chasing from 0.01% to 0.001%. SPICE gave better numbers the better I approached exact equality. Obviously this is Fun With Math, not real-world.

In real life the two halves of a 6080 will differ, so the "optimum" will be a little off of equality.

In practice I am not going to think about your bias because because you can adjust either upper grid divider or driver tube cathode bias and measure for equality or for lowest THD. Much faster than thinking.

My guess is that 300V into 6080 makes SO much more power than your headphones need that distortion will be quite low even when "not optimized".
 
S

steventrus

Member
Joined 2014
Question about Headphone Amp

I just finished building a morgan jones - white cathode follower headphone amp. The amp works, but has a very large hum in both channels. The power supply is a simple design with a bridge rectifier and a 330UF filtering capacitor for the plate voltage and a bridge rectifier and 2200UF filtering capacitor for the filament voltage.
 
PRR

PRR

Member
Joined 2003
Paid Member
You are right, the BBC.info site has lost their copies.

Paper copies "can" be found. I could get the set for about $100, shipped from England.
Television Engineering Principles and Practice Volume 1 by S.W. Amos and D.C. Birkinshaw
Television Engineering Principles and Practice Volume 2 Video-Frequency Amplification by S.W. Amos and D.C. Birkinshaw
TELEVISION ENGINEERING: Principles and Practice. Volume 3: Waveform Generation by Amos, S W & Birkinshaw
Television Engineering: Principles and Practice (Volume 4) by Amos SW et al: Poor (1958) | Anybook Ltd.

Shipping onward to Argentina would be more. Probably a lot more.

I too hope some PDFs turn up.
 
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