• 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.

LR8N3 as load anode CCS

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#5
You'll be ok @1m the safe operating area of the LR8N3 is 0.74W in the TO-92 package. Working the math backwards Vin-Vout for 10mA = 74V

Higher PSRR -- DN2540N3G, or a pair of them will make you a source with MegOhm impedance. SOA bounded by 1W. It's also TO-92, cost is $0.78 vs $0.64 for the LR8N3. See the second in Walt's series on current sources.

Supertex is now owned by Microchip, Mouser carries.
 
#7
jackinnj said:
You'll be ok @1m the safe operating area of the LR8N3 is 0.74W in the TO-92 package. Working the math backwards Vin-Vout for 10mA = 74V

Higher PSRR -- DN2540N3G, or a pair of them will make you a source with MegOhm impedance. SOA bounded by 1W. It's also TO-92, cost is $0.78 vs $0.64 for the LR8N3. See the second in Walt's series on current sources.

Supertex is now owned by Microchip, Mouser carries.
Click to expand...

In the end the usually cascode.

Other option: the LND150, maybe?

Thanks.
 
#9
> Usually a 100k...220k resistor is used at the anode of 12AX7 ... How much would the PSRR be with those resistors ?

Without looking, say 6dB.

Knowing some about the situation, as much as -9dB.

As a general thing, the B+ to a volt-amp stage should be clean enough to listen to, "silent", at the signal level and subsequent gain of that plate.

If you want to cheap-out, you can let B+ racket be a little higher R-loaded, much higher with a stiff CCS. OTOH a good CCS is about as many parts as a good voltage regulator/filter, which can also drop B+ crap way down. As can simple R-C filtering.
 
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