• 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.

Your opinions please

I haven't built the "free lunch" but I have built many "monkeys" (see Epsteins's page for the distinction.) Unless you build it exactly as Epstein did with the exact same power supply, these are not really beginner projects since they can require some juggling of resistor values and computations to figure out the needed values.

They are extremely clear sounding once you get the thing working properly thanks to the two stage design and the direct coupling. I would not suggest the 6C45P and battery bias for a beginner either. You would be better off with a the 6DJ8 family and LED bias; but again some engineering is required to get the amp to function at its best.
 
Here is an amp I built several years ago. The choke is by Electra Print although any choke with 100H at 15mA will work. Naturally the choke DCR will become part of the computation for the 2A3 bias resistor. This amp uses the 6N23P which works fine, but I found it far inferior in sound quality to the triode connected E180F (I am traveling and don't have the most recent schematics with me). So to build this amp you will have to be able to compute the two resistors in the cathode of the 2A3 to ensure both the 6N23P and 2A3 work in their most linear region.
 

Attachments

  • 2A3 SE drd amp.jpg
    2A3 SE drd amp.jpg
    164.2 KB · Views: 284

tasos25

Member
2013-02-13 1:19 pm
Here is an amp I built several years ago. The choke is by Electra Print although any choke with 100H at 15mA will work. Naturally the choke DCR will become part of the computation for the 2A3 bias resistor. This amp uses the 6N23P which works fine, but I found it far inferior in sound quality to the triode connected E180F (I am traveling and don't have the most recent schematics with me). So to build this amp you will have to be able to compute the two resistors in the cathode of the 2A3 to ensure both the 6N23P and 2A3 work in their most linear region.


Hello
I would like to ask what we use resistors to the cathode of 2a3(Watt).How much mA go through 2a3?
 
Last edited:
demetrios, your numbers look good, but I don't like the 10× rule. Why? Because by the time you get close to a 100 watt resistor, you are also looking at wire wound, or other semi-inductive mode. Better to just use 2.5× as a good figure, and let it be.

2.7 kΩ with 137 volts across it is yes, 9 W. × 2.5 = 22.5 or about 25 watts. This can be had nearly trivially with 5 ea 5 watt non-inductive standard resistors, either ⅕ the ohmage in series, or 5× the ohmage in parallel. Makes little difference. Could even do it with a bunch (10) 2 watt resistors, since they and dirt are about the same price.

20 ¢/ea for 2 watt, 270 Ω, metal film, qty 25+ … at mouser.com

GoatGuy
 

tasos25

Member
2013-02-13 1:19 pm
The amount of current through each resistor is marked on the schematic also notice that the voltages dropped by the resistors are marked on the schematic. Multiply the voltage by the current to get the wattage and then double that amount for safety.

Hello
I found in the forum below spreadsheet, and would like to ask if it applies to any pair of tubes, or for just the specifics Also what current flows in the transformer output? Current flowing through the tube output or the sum of the currents (tube output and protube)
sorry for my questions, I'm new in electronics
Thank you
View attachment updated_drd_calculator.zip